U.S. patent application number 11/943527 was filed with the patent office on 2009-04-23 for implantable and lumen-supporting stents and related methods of manufacture and use.
Invention is credited to Stuart Earl Kari, Riley King, Michael J. Lee.
Application Number | 20090105809 11/943527 |
Document ID | / |
Family ID | 39409981 |
Filed Date | 2009-04-23 |
United States Patent
Application |
20090105809 |
Kind Code |
A1 |
Lee; Michael J. ; et
al. |
April 23, 2009 |
IMPLANTABLE AND LUMEN-SUPPORTING STENTS AND RELATED METHODS OF
MANUFACTURE AND USE
Abstract
An implantable stent includes multiple circumferential segments
that surround a bore and are connected in series along a length to
form a tubular wall. Multiple adjacent alternating opposite facing
crowns arranged along each segment's circumference are bridged by
struts. The struts include a series of staggered arcuate edges with
limited flats to provide a limited region of maximum width between
significantly extended reducing diameter tapers at either end where
they transition into the crowns. Connections between adjacent
segments are wider and stiffer than the struts and strut-crown
transitions in the segments. The crowns include inner and outer
radii with off-set centers along a common axis to provide medial
crown peaks along the axis that are wider than the narrowed crown
shoulders on either side of the axis and from which the tapered
struts extend. Material strain and flexure along the stent during
lateral bending is distributed mainly within the segments, e.g.
along the struts or crowns, versus at the connections between
segments. Material strain and deformation during radial expansion
is principally concentrated at the crown shoulders and tapered
transition region with the struts. Particular closed-open-closed
arrangements along the stent length are disclosed, though with
fewer stent connections in the relatively "closed" end-portions
along the stent than are provided by other typically "open" cell
stents in prior use. Enhanced combinations of performance
characteristics are provided regarding visibility, trackability,
expansion characteristics, fatigue failures, coating integrity, and
local drug delivery from the stent.
Inventors: |
Lee; Michael J.; (Santa
Rosa, CA) ; Kari; Stuart Earl; (Windsor, CA) ;
King; Riley; (Rohnert Park, CA) |
Correspondence
Address: |
K&L Gates LLP;ATTN: Daniel S. Kim
1900 MAIN STREET, SUITE 600
IRVINE
CA
92614-7319
US
|
Family ID: |
39409981 |
Appl. No.: |
11/943527 |
Filed: |
November 20, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60981433 |
Oct 19, 2007 |
|
|
|
Current U.S.
Class: |
623/1.17 ;
623/1.15; 623/1.3; 623/1.33 |
Current CPC
Class: |
A61F 2/915 20130101;
A61F 2230/0054 20130101; A61F 2002/91541 20130101; A61F 2230/0069
20130101; A61F 2250/0031 20130101; A61F 2002/91575 20130101; A61F
2/91 20130101; A61F 2210/0076 20130101; A61F 2002/91558 20130101;
A61F 2250/0032 20130101; A61F 2250/0036 20130101; A61F 2250/0068
20130101; A61F 2250/0029 20130101; A61F 2210/0014 20130101; A61F
2250/0018 20130101 |
Class at
Publication: |
623/1.17 ;
623/1.15; 623/1.33; 623/1.3 |
International
Class: |
A61F 2/06 20060101
A61F002/06 |
Claims
1. An implantable medical stent system, comprising: a radially
expandable stent comprising a filamental structure in a pattern
surrounding a bore to form a substantially tubular wall along a
length relative to a longitudinal axis; wherein the filamental
structure comprises at least one arcuate crown with a crown peak
having a radius of curvature located along a reference axis, and
first and second arcuate crown shoulders on first and second sides,
respectively, of the reference axis; wherein the filamental
structure also comprises at least one pair of adjacent first and
second elongated struts extending from the first and second crown
shoulders, respectively; and wherein the arcuate crown peak
comprises at least one of (a) a peak width that is greater than at
least one of first and second shoulder widths along the first and
second respective crown shoulders, (b) an outer radius of curvature
about a first center that is offset from a second center of an
inner radius of curvature, and (c) a radial expansion
characteristic with a strain distribution that is substantially
lower than along at least one of the first and second crown
shoulders.
2. An implantable medical stent system, comprising: a radially
expandable stent comprising a plurality of adjacent circumferential
segments that comprise patterned filamental structures that
surround a bore and are arranged in series along a length relative
to a longitudinal axis to thereby form a substantially tubular wall
along the length; wherein each pair of adjacent segments is
connected by at least one of a plurality of connections between
segments; and wherein each connection comprises at least one of (a)
a longitudinal bending stiffness that is greater than a
longitudinal bending stiffness along either adjacent segment such
that upon an applied force of deflection lateral to the
longitudinal axis the stent exhibits more longitudinal flexure
within the segments than at the connections, and (b) a minimum
width that is greater than a minimum width along a patterned
filamental structure comprised by at least one of the adjacent
segments.
3. An implantable medical stent system, comprising: a radially
expandable stent comprising a filamental structure in a pattern
forming a substantially tubular wall surrounding a bore along a
length relative to a longitudinal axis, and with a plurality of
adjacent alternating opposite facing arcuate crowns bridged by a
plurality of elongated struts; wherein each crown comprises an
arcuate crown peak with a radius of curvature located along a
reference axis, and first and second arcuate crown shoulders on
first and second opposite sides, respectively, of the reference
axis; wherein each elongated strut extends over a length with an
intermediate portion located between first and second end portions
along the strut length, and also with inner and outer opposite
edges relative to the reference axis; wherein the first and second
end portions of each strut are coupled to the first and second
crown shoulders, respectively, of first and second adjacent
opposite facing crowns, respectively; and wherein each strut
comprises at least one of (a) a maximum width along the
intermediate portion that is greater than a width along the first
and second end portions and that extends over less than one-half of
the strut length, (b) a maximum width along the intermediate
portion that is substantially greater than a radial thickness
thereof; (c) a maximum width that is substantially greater than a
width of the respectively adjacent crowns at either a crown
shoulder or a crown peak thereof; (d) inner and outer radii along
the inner and outer edges of the first end portion and that are
substantially similar to outer and inner radii along the outer and
inner edges of the second end portion, and (e) inner and outer
substantially straight regions along the respective inner and outer
opposite edges that are substantially offset such that a majority
of each straight region does not overlap with the other straight
region along the strut length and is associated with an arcuate
region along the opposite edge.
4. An implantable medical stent system, comprising: a radially
expandable stent comprising a filamental structure in a pattern
surrounding a bore to form a substantially tubular wall along a
length relative to a longitudinal axis; wherein the filamental
structure comprises at least one high strain region and at least
one low strain region along the pattern; wherein the filamental
structure comprises a material strain distribution under deflection
force of lateral bending or radial expansion relative to the
longitudinal axis that is principally locally concentrated along
the high strain region; and wherein the low strain region comprises
at least one of (a) a width in a circumferential plane around the
longitudinal axis that is substantially greater than a width of the
high strain region along the longitudinal axis, (b) a width that is
substantially greater than a radial thickness at the respective low
strain region, and (c) a substantially increased radiopacity versus
the high strain region.
5. A method of deflecting a stent for at least one of radial
expansion and lateral bending of the stent, comprising: applying a
deflection force onto the stent for at least one of radial
expansion and lateral bending of the stent; wherein in response to
the deflection force the stent undergoes a material strain that is
principally locally distributed along at least one of (a) a
plurality of adjacent circumferential segments that surround a bore
and are connected in series to form a substantially tubular wall
along a longitudinal axis, and (b) a patterned filamental structure
of the stent at a plurality of transition regions where a plurality
of struts of the filamental structure extend between a plurality of
crown shoulders of a plurality of opposite facing crowns of the
filamental structure.
6. The system of claim 1, wherein: the filamental structure pattern
further comprises a plurality of adjacent circumferential segments
surrounding the bore and that are provided in series along the
length; the filamental structure pattern of each segment comprises
a plurality of said arcuate crowns in alternating opposite facing
orientations along a circumference of the segment surrounding the
bore, and a plurality of said pairs of struts, such that each pair
of adjacent struts bridge the shoulders of one crown with a
shoulder of each next adjacent opposite facing crown, respectively;
and each adjacent pair of segments is connected by at least one
connection.
7. The system of claim 4, wherein: the filamental structure pattern
further comprises a plurality of adjacent circumferential segments
surrounding the bore and that are provided in series along the
length; the filamental structure pattern of each segment comprises
a plurality of arcuate crowns with each crown having an arcuate
crown peak with a radius of curvature located along a reference
axis and first and second arcuate crown shoulders on first and
second opposite sides, respectively, of the reference axis, said
crowns being in alternating opposite facing orientations along a
circumference of the segment surrounding the bore, and comprising a
plurality of pairs of adjacent struts bridging between opposite
facing adjacent the crowns in the respective segment, such that
each pair of adjacent struts bridge the shoulders of one crown with
a shoulder of each next adjacent opposite facing crown,
respectively; and each adjacent pair of segments is connected by at
least one connection.
8. The system of claim 6, wherein each arcuate crown peak comprises
a peak width, the first and second shoulders comprise first and
second shoulder widths, and the peak width is greater than each of
the first and second shoulder widths.
9. The system of claim 6, wherein each arcuate crown peak comprises
an outer radius of curvature about a first center located along the
reference axis, and an inner radius of curvature about a second
center that is offset from the first center along the reference
axis.
10. The system of claim 9, wherein the first center of the inner
radius of curvature of the crown peak is offset away from the crown
peak on the reference axis relative to the second center of the
outer radii of curvature of the crown peak, such that the second
center is closer to the crown peak than the first center.
11. The system of claim 6, wherein the strain distribution relative
to each crown during radial expansion of the stent comprises
substantially higher strain along the first and second crown
shoulders than along the crown peak.
12. The system of claim 6, wherein each arcuate crown peak
comprises a peak width that is greater than first and second
shoulder widths along the first and second respective crown
shoulders, an outer radius of curvature about a first center that
is offset from a second center of an inner radius of curvature
along the reference axis, and a radial expansion characteristic
with a strain distribution that is substantially lower than along
each of the first and second crown shoulders.
13. The system of claim 6, wherein each connection comprises a
lateral bending stiffness that is greater than a lateral bending
stiffness along at least one respectively adjacent segment, such
that upon an applied force of deflection lateral to the
longitudinal axis the stent undergoes more flexure within the
segments than at the connections.
14. The system of claim 2, wherein each connection comprises a
minimum width that is greater than a minimum width along each
adjacent segment.
15. The system of claim 14, wherein the minimum width of each
connection is greater than a maximum width along each respectively
adjacent segment.
16. The system of claim 3, wherein each strut comprises a maximum
width along an intermediate portion thereof that is greater than
along first and second end portions thereof that couple to first
and second opposite facing crowns, and which maximum length of the
intermediate portion extends along less than about one-half of the
length of the strut.
17. The system of claim 16, wherein the maximum width of the
intermediate portion is at a substantially discrete location along
the strut and does not extend over a significant length of the
strut.
18. The system of claim 2, wherein each strut comprises a maximum
width along an intermediate portion thereof that is substantially
greater than a radial thickness thereof.
19. The system of claim 3, wherein each strut comprises a maximum
width that is substantially greater than a width of the
respectively adjacent crowns at either a crown shoulder or a crown
peak thereof.
20. The system of claim 3, wherein each strut comprises a region of
overlap between inner and outer opposite straight regions that is
less than about one-half of the length of the strut.
21. The system of claim 3, wherein each strut comprises each of: a
maximum width along the intermediate portion that is greater than a
width along the first and second end portions and that extends over
less than one-half of the strut length, and that is also
substantially greater than a radial thickness thereof the
intermediate portion, and that is also greater than a width of the
respectively adjacent crowns at the crown shoulders thereof; inner
and outer radii along the inner and outer edges of the first end
portion and that are substantially similar to outer and inner radii
along the outer and inner edges of the second end portion; and
inner and outer substantially straight regions along the respective
inner and outer opposite edges that are substantially offset such
that a majority of each straight region does not overlap with the
other straight region along the strut length and is associated with
an arcuate region along the opposite edge.
22. The system of claim 3, wherein: first and second crowns of said
adjacent opposite facing crowns are bridged by a strut; the first
and second crowns comprise respective arcuate peaks with respective
radii of curvature centered along first and second reference axes,
respectively, and with each respective arcuate crown also
comprising first and second arcuate shoulders located on first and
second opposite respective sides of the respective reference axis;
each elongated strut extends over a length between first and second
end portions that are coupled to first and second respective
shoulders of the first and second crowns, respectively; each
elongated strut comprises an inner edge and an outer edge along the
length relative to the first reference axis; the inner edge along
the first end portion comprises a first arcuate region extending
over a first length with a first radius of curvature away from the
first reference axis and toward the second reference axis; the
inner edge along the second end portion comprises a second arcuate
region extending over a second length with a second radius of
curvature toward the first reference axis and away from the second
reference axis; the outer edge along the first end portion
comprises a third arcuate region extending over a third length with
a third radius of curvature away from the first reference axis and
toward the second reference axis; the outer edge along the second
end portion comprises a fourth arcuate region extending over a
fourth length with a fourth radius of curvature toward from the
first reference axis and away from the second reference axis; the
first and third arcuate regions differ with respect to at least one
of their respective radii of curvature and length; the first and
fourth arcuate regions are substantially similar with respect to at
least one of their respective radii of curvature and length; and
the second and third arcuate regions are substantially similar with
respect to at least one of their respective radii of curvature and
length.
23. The system of claim 3, wherein: each elongated strut extends
over a length between first and second end portions that are
coupled to and integral with first and second respective shoulders
of first and second adjacent opposite facing crowns, respectively;
each elongated strut comprises an inner edge and an outer edge
along the length relative to the reference axis of the first
adjacent crown; the inner edge along the first end portion
comprises a first arcuate region with a first radius of curvature
away from the reference axis and that extends from the first crown
shoulder to a first location along the strut; the outer edge along
the first end portion comprises a second arcuate region with a
second radius of curvature away from the reference axis and that
extends from the first crown shoulder to a second location along
the strut that is closer to the first crown shoulder than the first
location; and the outer edge further comprises a substantially
straight edge region extending at least from the second location to
the first location along the strut and that coincides at least in
part with a portion of the first arcuate region along the inner
edge.
24. The system of claim 1, wherein: the stent comprises a substrate
material with a surface; a coating is located on the surface; and
the bioactive agent is stored by and elutes from the coating at the
location.
25. The system of claim 1, wherein: the stent comprises a plurality
of discrete reservoirs within a metal scaffold filament; and the
bioactive agent is housed within and elutes from the reservoirs at
the location.
26. The system of claim 2, wherein a majority or all connections
comprise each of characteristics (a)-(c) relative to the
respectively adjacent segments.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit under 35 U.S.C.
.sctn.119(e) of U.S. Provisional Patent Applications No. 60/981,433
filed Oct. 19, 2007 which is incorporated by reference herein in
its entirety.
FIELD OF THE INVENTION
[0002] This invention relates to implantable medical devices. More
specifically, the invention relates to implantable and
lumen-supporting stents. Still more specifically, it relates to
such stents for the treatment or inhibition of stenoses in coronary
or peripheral vessels in humans.
BACKGROUND OF THE INVENTION
[0003] Cardiovascular disease, including atherosclerosis, is the
leading cause of death in the United States. The medical community
has developed a number of methods and devices for treating coronary
heart disease, some of which are specifically designed to treat the
complications resulting from atherosclerosis and other forms of
coronary vessel narrowing.
[0004] An important development for treating atherosclerosis and
other forms of vascular narrowing is percutaneous transluminal
angioplasty, hereinafter referred to as "angioplasty." The
objective of angioplasty is to enlarge the lumen of an affected
vessel by radial hydraulic expansion. The procedure is accomplished
by inflating a balloon within the narrowed lumen of the affected
vessel. Radial expansion of the affected vessel occurs in several
different dimensions, and is related to the nature of the plaque
narrowing the lumen. Soft, fatty plaque deposits are flattened by
the balloon, while hardened deposits are cracked and split to
enlarge the lumen. The wall of the affected vessel itself is also
stretched when the balloon is inflated.
[0005] Unfortunately, while the affected vessel can be enlarged
thus improving blood flow, in some instances the vessel re-occludes
chronically ("restenosis"), or closes down acutely ("abrupt
reclosure"), negating the positive effect of the angioplasty
procedure. Such restenosis or abrupt reclosure frequently
necessitates repeat angioplasty or open heart surgery. While such
restenosis or abrupt reclosure does not occur in the majority of
cases, it occurs frequently enough that such complications comprise
a significant percentage of the overall failures of the angioplasty
procedure, for example, twenty-five to thirty-five percent of such
failures.
[0006] To lessen the risk of restenosis and abrupt closure, various
devices have been proposed for mechanically keeping the affected
vessel open after completion of the angioplasty procedure. Such
endoprostheses (generally referred to as "stents"), are typically
inserted into the vessel, positioned across the lesion or stenosis,
and then expanded to keep the passageway clear. The stent provides
a scaffold which overcomes the natural tendency of the vessel walls
of some patients to renarrow, thus maintaining the openness of the
vessel and resulting blood flow.
[0007] While stents and stent applications of the type described
have been found to work well in a number of patients, there is
still room for improvement. First, various areas of the vasculature
and different treatment sites call for stents with different
characteristics. For example, a stent that must travel through a
tortuous and highly-curved area of the vasculature to reach a
particular treatment site would benefit from enhanced flexibility
characteristics that are not necessarily needed in a stent used to
treat an easily-accessible treatment site. Likewise, a stent that
will be deployed at an area of a vessel that has a branch or
bifurcation would benefit from flexibility characteristics not
necessarily needed in a stent used to treat a relatively straight
and uniform portion of a vessel.
[0008] Further, as stents are presently used, there can be an
abrupt transition between the area of a vessel that is contacted by
the stent (and thus receiving the benefits of the stent) and those
portions of the vessel that are not. This abrupt transition between
stented and unstented portions of a vessel can exacerbate the
physiological trauma found at a treatment site. Thus, in some
instances, a stent with characteristics that provide for a less
abrupt transition between stented and unstented portions of a
vessel may be advantageous.
[0009] Notwithstanding the foregoing, however, another frequent
observation is that balloon expanded stents first deploy open under
balloon inflation at their ends, with middle portion of the stent
to follow. This is often referred to as "dog-boning" and has been
suspected to result, in some cases, in increased trauma at end
margins of treated areas. Because stent ends can deploy before
middle stent regions and at lower balloon pressures, it would be
considered advantageous to provide a new and improved stent that
counteracts this with more uniform stent expansion. In particular
cases where a stent may maintain a design with particularly
beneficial lateral flexibility over its length, it would be
desirable to also provide features at or adjacent the ends to
result in a more uniform expansion over the length and including
the stent ends.
[0010] Characteristics that result in low restenosis rates are also
considered highly beneficial for most stent uses, such as for
example for endovascular stents in particular. One such beneficial
characteristic would be one that combats restenosis at locations
along or adjacent the treatment site where restenosis is more
frequently observed to occur, such as for example the area of the
vessel nearest to the proximal (e.g. "upstream" portion, as related
to blood flow) end of the stent. Other such characteristics include
for example enhanced tissue-device interface between the stent and
tissue being implanted. Such enhancements may for example reduce
trauma, reduce a restenotic or other undesired biological response
to the implant, or otherwise benefit other aspects of the stent's
intended use. In one particular regard, a pattern chosen for a
stent scaffold, such as per undulating sinusoidal or "serpentine"
strut-crown scaffolds most frequently used, may impact their
capabilities in their use and/or with respect to outcomes.
According to one more specific example, relative stiffnesses
(including lateral, radial, or both) and geometries of crowns,
struts, the connections or transitions between "segments" along a
stent, and how these aspects relate to each other within an overall
design, can have distinct impact on their in vivo use and
outcomes.
[0011] It is also to be appreciated that certain stents, and their
respective features related to their performance, are relatively
small to the basic human observation skills such as sight and
touch. The difference between features of one stent and another may
appear very subtle, or not even readily noticeable, to initial
visual or tactile observation. However, such otherwise subtle
changes in or differences between such features may significantly
impact the use of these devices, especially where intended for
percutaneous transluminal delivery and chronic in vivo implantation
within dynamic biological tissues such as blood vessels.
[0012] While endolumenal vascular stents have clearly become the
most prominent type of stents used in medicine, it is also
appreciated that stents may be, and have been, implanted in other
regions of the body. For example, stents have been either proposed
or used in other body lumens or spaces, such as without limitation
within gastrointestinal tract, pulmonary system, urinary tract
system, etc.
[0013] Various needs still remain for providing stents with
improved features, including without limitation in order to
beneficially improve various combinations of performance aspects
such as trackability, visibility, expansion characteristics (e.g.
uniformity of expansion, recoil, etc.), material fatigue and yield
failure, tissue-device interface, surface coating adhesion and
integrity, local drug delivery, and biological response and
outcomes from their implantation.
SUMMARY OF THE INVENTION
[0014] One aspect of the present disclosure provides a stent system
with an improved stent. According to one embodiment, the stent
includes improved expansion characteristics. According to another
embodiment, the stent includes improved lateral bending
characteristics. In one particular embodiment, the stent undergoes
lateral or radial deflection with strain distribution primarily at
transition regions between struts and crown shoulders on opposite
sides of crown peaks of the stent's filamental pattern. In another
embodiment, the stent includes geometry along crown regions that
differ from strut geometry, providing enhanced deflection
characteristics in combination with enhanced characteristics along
the strut, such as for example for drug delivery or visibility.
[0015] Another aspect of the present disclosure is an implantable
medical stent system with a radially expandable stent comprising a
filamental structure in a pattern surrounding a bore to form a
substantially tubular wall along a length relative to a
longitudinal axis. The filamental structure comprises at least one
arcuate crown with a crown peak having a radius of curvature
located along a reference axis, and first and second arcuate crown
shoulders on first and second sides, respectively, of the reference
axis. The filamental structure also comprises at least one pair of
adjacent first and second elongated struts extending from the first
and second crown shoulders, respectively.
[0016] The arcuate crown peak comprises at least one of: (a) a peak
width that is greater than at least one of first and second
shoulder widths along the first and second respective crown
shoulders; (b) an outer radius of curvature about a first center
that is offset from a second center of an inner radius of
curvature; and (c) a radial expansion characteristic with a strain
distribution that is substantially lower than along at least one of
the first and second crown shoulders. According to a further mode,
the crown peak comprises a combination of at least two of these
particularly beneficial features. In a still further embodiment,
the crown peak comprises each of these features.
[0017] Another aspect of the present disclosure is an implantable
medical stent system with a radially expandable stent comprising a
plurality of adjacent circumferential segments that comprise
patterned filamental structures that surround a bore and are
arranged in series along a length relative to a longitudinal axis
to thereby form a substantially tubular wall along the length. Each
pair of adjacent segments is connected by at least one of a
plurality of connections between segments.
[0018] In certain further embodiments, at least one (and in further
particular embodiments a majority of or each) connection comprises
at least one of: (a) a longitudinal bending stiffness that is
greater than a longitudinal bending stiffness along either adjacent
segment such that upon an applied force of deflection lateral to
the longitudinal axis the stent exhibits more longitudinal flexure
within the segments than at the connections; and (b) a minimum
width that is greater than a minimum width along a patterned
filamental structure comprised by at least one of the adjacent
segments.
[0019] According to a further embodiment, each connection comprises
a combination or all of these features.
[0020] Another aspect of the present disclosure is an implantable
medical stent system with a radially expandable stent comprising a
filamental structure in a pattern forming a substantially tubular
wall surrounding a bore along a length relative to a longitudinal
axis, and with a plurality of adjacent alternating opposite facing
arcuate crowns bridged by a plurality of elongated struts. Each
crown comprises an arcuate crown peak with a radius of curvature
located along a reference axis, and first and second arcuate crown
shoulders on first and second opposite sides, respectively, of the
reference axis. Each elongated strut extends over a length with an
intermediate portion located between first and second end portions
along the strut length, and also with inner and outer opposite
edges relative to the reference axis. The first and second end
portions of each strut are coupled to the first and second crown
shoulders, respectively, of first and second adjacent opposite
facing crowns, respectively.
[0021] According to certain further embodiments of this aspect,
each strut comprises at least one of: (a) a maximum width along the
intermediate portion that is greater than a width along the first
and second end portions and that extends over less than one-half of
the strut length; (b) a maximum width along the intermediate
portion that is substantially greater than a radial thickness
thereof; (c) a maximum width that is substantially greater than a
width of the respectively adjacent crowns at either a crown
shoulder or a crown peak thereof; (d) inner and outer radii along
the inner and outer edges of the first end portion and that are
substantially similar to outer and inner radii along the outer and
inner edges of the second end portion, and (e) inner and outer
substantially straight regions along the respective inner and outer
opposite edges that are substantially offset such that a majority
of each straight region does not overlap with the other straight
region along the strut length and is associated with an arcuate
region along the opposite edge.
[0022] According to a further embodiment, the struts comprise a
combination of at least two of these features. In still further
embodiments, the struts comprise a combination of three, four, and
even each of these features providing further benefit in their
combinations.
[0023] Another aspect of the present disclosure is an implantable
medical stent system with a radially expandable stent comprising a
filamental structure in a pattern surrounding a bore to form a
substantially tubular wall along a length relative to a
longitudinal axis. The filamental structure comprises at least one
high strain region and at least one low strain region along the
pattern. The filamental structure comprises a material strain
distribution under deflection force of lateral bending or radial
expansion relative to the longitudinal axis that is principally
locally concentrated along the high strain region.
[0024] In another embodiment, the low strain region comprises at
least one of (a) a width in a circumferential plane around the
longitudinal axis that is substantially greater than a width of the
high strain region along the longitudinal axis, (b) a width that is
substantially greater than a radial thickness at the respective low
strain region, and (c) a substantially increased radiopacity versus
the high strain region.
[0025] According to further embodiments, the struts comprise a
combination of two and even each of these individual features
providing further benefit in their combinations.
[0026] Another aspect of the present disclosure is a method of
deflecting a stent for at least one of radial expansion and lateral
bending of the stent. This method includes applying a deflection
force onto the stent for at least one of radial expansion and
lateral bending of the stent. Further to this method, in response
to the deflection force the stent undergoes a material strain that
is principally locally distributed along at least one of: (a) a
plurality of adjacent circumferential segments that surround a bore
and are connected in series to form a substantially tubular wall
along a longitudinal axis, and (b) a patterned filamental structure
of the stent at a plurality of transition regions where a plurality
of struts of the filamental structure extend between a plurality of
crown shoulders of a plurality of opposite facing crowns of the
filamental structure.
[0027] According to a further embodiment, the stent exhibits a
combination of each of these characteristics. In another mode, the
stent exhibits such combination of characteristics in each of
radial expansion and lateral bending.
[0028] Various additional modes, embodiments, features, and
variations are also contemplated with respect to these various
aspects and modes, providing still further benefit and utility.
[0029] According to one such further embodiment, a system according
to one or more the present aspects and embodiments includes a
filamental structure pattern along a plurality of adjacent
circumferential segments surrounding the bore and that are provided
in series along the length. The filamental structure pattern of
each segment comprises a plurality of arcuate crowns in alternating
opposite facing orientations along a circumference of the segment
surrounding the bore, and a plurality of pairs of struts, such that
each pair of adjacent struts bridge the shoulders of one crown with
a shoulder of each next adjacent opposite facing crown,
respectively. Each adjacent pair of segments is connected by at
least one connection.
[0030] In another embodiment of the system described above, the
filamental pattern further comprises a plurality of adjacent
circumferential segments surrounding the bore and that are provided
in series along the length. The filamental structure pattern of
each segment comprises a plurality of arcuate crowns with each
crown having an arcuate crown peak with a radius of curvature
located along a reference axis and first and second arcuate crown
shoulders on first and second opposite sides, respectively, of the
reference axis, the crowns being in alternative opposite facing
orientations along a circumference of the segment surrounding the
bore and comprising a plurality of pairs of adjacent struts
bridging between opposite facing adjacent crowns in the respective
segment such that each pair of adjacent struts bridge the shoulders
of one crown with a shoulder of each next adjacent opposite facing
crown, respectively. In another embodiment, each adjacent pair of
segments is connected by at least one connection.
[0031] In another embodiment for a system such as described above,
each of a plurality of arcuate crown peaks comprises a peak width,
the first and second shoulders comprise first and second shoulder
widths, and the peak width is greater than each of the first and
second shoulder widths.
[0032] In another embodiment for a system such as described above,
each of a plurality of arcuate crown peaks comprises an outer
radius of curvature about a first center located along the
reference axis, and an inner radius of curvature about a second
center that is offset from the first center along the reference
axis.
[0033] According to one embodiment, the first center of the inner
radius of curvature of the crown peak is offset away from the crown
peak on the reference axis relative to the second center of the
outer radii of curvature of the crown peak, such that the second
center is closer to the crown peak than the first center.
[0034] In another embodiment for a system such as described above,
the strain distribution relative to each of a plurality of crowns
during radial expansion of the stent comprises substantially higher
strain along the first and second crown shoulders than along the
crown peak.
[0035] In one embodiment, the strain distribution is substantially
bifurcated and principally located along each of first and second
transition regions between the first and second crown shoulders and
first and second struts extending therefrom, respectively.
[0036] In another embodiment for a system such as described above,
each of a plurality of arcuate crown peaks comprises a peak width
that is greater than first and second shoulder widths along the
first and second respective crown shoulders, an outer radius of
curvature about a first center that is offset from a second center
of an inner radius of curvature along the reference axis, and a
radial expansion characteristic with a strain distribution that is
substantially lower than along each of the first and second crown
shoulders.
[0037] In another embodiment for a system such as described above,
each of a plurality of connections between adjacent segments of a
stent comprises a lateral bending stiffness that is greater than a
lateral bending stiffness along at least one respectively adjacent
segment, such that upon an applied force of deflection lateral to
the longitudinal axis the stent undergoes more flexure within the
segments than at the connections.
[0038] According to one embodiment, each connection comprises a
lateral bending stiffness that is greater than a lateral bending
stiffness of each respectively adjacent segment.
[0039] In another embodiment for a system such as described
hereunder, each of a plurality of connections between adjacent
segments of a stent comprises a minimum width that is greater than
a minimum width along each adjacent segment.
[0040] According to one embodiment, the minimum width of each
connection is greater than a maximum width of at least one of a
crown or strut in at least one respectively adjacent segment. In
another embodiment, the minimum width of each connection is greater
than a maximum width of a majority of the crowns and struts in at
least one respectively adjacent segment. In another embodiment, the
minimum width of each connection is greater than a maximum width of
all crowns and struts of at least one respectively adjacent
segment. In another embodiment, the minimum width of each
connection is greater than a maximum width along each respectively
adjacent segment. In another embodiment, the minimum width of each
connection is greater than a minimum width along a crown, strut, or
transition region between crown and strut, in each respectively
adjacent segment.
[0041] According to still another embodiment of the various aspects
noted hereunder, each of a plurality of struts in a filamental
structure of a stent comprises a maximum width along an
intermediate portion thereof that is greater than along first and
second end portions thereof that couple to first and second
opposite facing crowns, and which maximum length of the
intermediate portion extends along less than about one-half of the
length of the strut.
[0042] According to one embodiment, the maximum width of the
intermediate portion extends along less than about one-quarter of
the length of the strut. In another embodiment, the maximum width
of the intermediate portion is at a substantially discrete location
along the strut and does not extend over a significant length of
the strut. In still another embodiment, the first and second end
portions of each strut comprises a tapering width reduction from
the intermediate portion to first and second respectively coupled
crown shoulders, such that the first and second end portions
comprise first and second stiffness transition regions from the
intermediate portion to the first and second adjacent crowns.
[0043] According to another further embodiment of the various
system aspects described hereunder, each of a plurality of stent
struts comprises a maximum width along an intermediate portion
thereof that is substantially greater than a radial thickness
thereof.
[0044] In one embodiment, the maximum width of the strut along the
intermediate portion is at least about 25% greater than the radial
thickness of the strut along the intermediate portion. In another
embodiment, the maximum width of the strut along the intermediate
portion is at least about 50% greater than the radial thickness of
the strut along the intermediate portion. In further embodiments,
the maximum width may be as much as 75% or greater than the radial
thickness of the strut. However, in some applications, excessive
width may provide detriment to certain performance related
characteristics. Accordingly, as for such considerations in certain
settings, further embodiments of the present disclosure include
each such lower limit range noted above, but with its respective
range being further limited at an upper limit that is equivalent to
the other greater "at least" lower limits also noted.
[0045] In another embodiment, the maximum width of the strut along
the intermediate portion is between about 0.0030 and 0.0050 inches,
and the radial thickness of the strut along the intermediate
portion is between about 0.0020 and about 0.0040 inches. In a
further embodiment, the maximum width is between about 0.0035 and
0.0050 inches, with radial thickness between about 0.0030 and about
0.0040 inches.
[0046] These ranges (and other dimensional ranges provided
hereunder) are considered of benefit in certain cardiovascular
stenting applications for example, such as coronary stenting.
Similarly adjusted ranges are contemplated, but with appropriately
shifted magnitude of the respective limits with respect to either
smaller or larger stents, or with more or fewer crowns, as would be
apparent to one of ordinary skill.
[0047] According to still another embodiment, each of a plurality
of stent struts comprises a maximum width that is substantially
greater than a width of the respectively adjacent crowns at either
a crown shoulder or a crown peak thereof.
[0048] In one embodiment, the maximum width of the strut along the
intermediate portion is greater than a width of the respectively
adjacent crowns at the respective crown peaks. In a further
embodiment, the maximum width of the strut along the intermediate
portion is at least about 20% greater than the width at the
adjacent crown peaks. In a still further embodiment, it is at least
35% greater. In another embodiment, it is at least 50% greater.
Again, in certain instances (and representing still further
embodiments), such greater width may be limited at upper ends of
ranges as well, such as similarly noted for other respective
dimensional considerations above.
[0049] In another embodiment, the maximum width of the strut along
the intermediate portion is greater than a width of at least one
respectively adjacent crown at least at one crown shoulder of the
crown.
[0050] In another embodiment, the maximum width of the strut along
the intermediate portion is greater than a width at each crown
shoulder.
[0051] In another embodiment, the maximum width of the strut along
the intermediate portion is at least about 25% greater than a width
at the crown shoulder.
[0052] In another embodiment of certain systems noted hereunder,
each of a plurality of stent struts comprises a region of overlap
between inner and outer opposite straight regions that is less than
about one-half of the length of the strut. In one embodiment, the
region of overlap is less than about one-fourth of the length of
the strut. In a further embodiment, the region of overlap is less
than about one-eighth of the length of the strut.
[0053] In still a further embodiment, each of a plurality of stent
struts comprises each of: a maximum width along its intermediate
portion that is greater than a width along its first and second end
portions and that extends over less than about one-half of the
strut length, and that is also substantially greater than a radial
thickness thereof the intermediate portion, and that is also
greater than a width of the respectively adjacent crowns at the
crown shoulders thereof; inner and outer radii along the inner and
outer edges of the first end portion and that are substantially
similar to outer and inner radii along the outer and inner edges of
the second end portion; and inner and outer substantially straight
regions along the respective inner and outer opposite edges that
are substantially offset such that a majority of each straight
region does not overlap with the other straight region along the
strut length and is associated with an arcuate region along the
opposite edge.
[0054] In still a further embodiment, first and second crowns of
adjacent opposite facing crowns in a stent segment are bridged by a
strut. The first and second crowns comprise respective arcuate
peaks with respective radii of curvature centered along first and
second reference axes, respectively, and with each respective
arcuate crown also comprising first and second arcuate shoulders
located on first and second opposite respective sides of the
respective reference axis. Each elongated strut extends over a
length between first and second end portions that are coupled to
first and second respective shoulders of the first and second
crowns, respectively. Each elongated strut also comprises an inner
edge and an outer edge along the length relative to the first
reference axis. The inner edge along the first end portion
comprises a first arcuate region extending over a first length with
a first radius of curvature away from the first reference axis and
toward the second reference axis. The inner edge along the second
end portion comprises a second arcuate region extending over a
second length with a second radius of curvature toward the first
reference axis and away from the second reference axis. The outer
edge along the first end portion comprises a third arcuate region
extending over a third length with a third radius of curvature away
from the first reference axis and toward the second reference axis.
The outer edge along the second end portion comprises a fourth
arcuate region extending over a fourth length with a fourth radius
of curvature toward from the first reference axis and away from the
second reference axis. The first and third arcuate regions differ
with respect to at least one of their respective radii of curvature
and length, the first and fourth arcuate regions are substantially
similar with respect to at least one of their respective radii of
curvature and length, and the second and third arcuate regions are
substantially similar with respect to at least one of their
respective radii of curvature and length.
[0055] According to another embodiment, each of a plurality of
elongated stent struts extends over a length between first and
second end portions that are coupled to and integral with first and
second respective shoulders of first and second adjacent opposite
facing crowns, respectively. Each elongated strut comprises an
inner edge and an outer edge along the length relative to the
reference axis of the first adjacent crown. The inner edge along
the first end portion comprises a first arcuate region with a first
radius of curvature away from the reference axis and that extends
from the first crown shoulder to a first location along the strut.
The outer edge along the first end portion comprises a second
arcuate region with a second radius of curvature away from the
reference axis and that extends from the first crown shoulder to a
second location along the strut that is closer to the first crown
shoulder than the first location. The outer edge further comprises
a substantially straight edge region extending at least from the
second location to the first location along the strut and that
coincides at least in part with a portion of the first arcuate
region along the inner edge.
[0056] According to still another embodiment, each of a plurality
of adjacent interconnected stent segments comprises a first
plurality of similarly oriented facing crowns that each faces and
is aligned with a unique one of a second plurality of opposite
oriented facing crowns, relative to the first plurality, of another
adjacent segment. A plurality of the connections are located at
each of a plurality of locations between each adjacent pair of
segments along the length. Each of the plurality of connections at
each location connects first and second opposite relative facing
crowns of the first and second pluralities of the first and second
adjacent segments, respectively.
[0057] In still another embodiment, a delivery system is coupled to
the stent and is configured to deliver the stent to a location
within a body of a patient and implant the stent at the location.
In one embodiment, the stent is balloon expandable and the delivery
system is a balloon catheter. In another embodiment, the stent is
self-expandable and the delivery system comprises an outer
retention sheath or tether system. In another embodiment, the
delivery system comprises a guidewire. In another embodiment, the
delivery system comprises an actuator to deploy the stent, e.g.
such as an inflation device for balloon expansion.
[0058] In another embodiment, a bioactive agent is provided in a
preparation configured for delivery into a patient and adapted to
provide combination therapy with the stent implanted at a location
within a body of the patient. According to one embodiment, the
stent comprises a substrate material with a surface, a coating is
located on the surface, and the bioactive agent is stored by and
elutes from the coating at the location. In another embodiment, the
stent comprises a plurality of discrete reservoirs within a metal
scaffold filament, and the bioactive agent is housed within and
elutes from the reservoirs at the location.
[0059] In another present embodiment, the stent comprises a
filamental material that comprises a metal. In further embodiments,
the metal may be for example stainless steel, nickel titanium
alloy, or cobalt-chromium alloy. According to one still further
metal alloy for such uses, a cobalt-chromium alloy is used that is
of the L-605 cobalt-chromium type alloy.
[0060] In another embodiment, each of a plurality of connections
between adjacent stent segments comprises a cross-over between
portions of a continuous integral material corresponding with each
adjacent segment.
[0061] In another embodiment, each of a plurality of connections
between adjacent stent segments comprises a connector extending
between portions of filamental material in each adjacent
segment.
[0062] In another embodiment, each connection comprises a weld
joint between portions of filamental material in each adjacent
segment.
[0063] In another embodiment of the present method aspects
presented hereunder, such method further includes applying a
lateral deflection force for lateral bending, wherein in response
to a lateral bending deflection force, the stent undergoes a
material strain that is principally locally distributed along the
plurality of adjacent circumferential segments.
[0064] In one embodiment, the material strain along the plurality
of adjacent circumferential segments is principally distributed
along a patterned filamental structure within the segments at a
plurality of transition regions where a plurality of struts of the
filamental structure extend between a plurality of crown shoulders
of a plurality of opposite facing crowns of the filamental
structure.
[0065] In another further method embodiment, the steps further
include applying the deflection force onto the stent for radial
expansion of the stent. In response to this deflection force, the
stent undergoes a material strain that is principally locally
distributed along a patterned filamental structure of the stent at
a plurality of transition regions where a plurality of struts of
the filamental structure extend between a plurality of crown
shoulders of a plurality of opposite facing crowns of the
filamental structure. In one embodiment, the principally locally
distributed material strain along the patterned filamental
structure is located within the plurality of adjacent connected
segments.
[0066] It is to be appreciated that each of the various aspects,
modes, embodiments, features, and variations noted above is
considered to be independently valuable and beneficial without
requiring necessary combination(s) with the others. However, it is
also appreciated that such further combinations are also
contemplated to provide still further benefits and value, and also
within the scope of the present disclosure. Other aspects, modes,
embodiments, features, and variations will be apparent to one of
ordinary skill upon further review of the detailed embodiments set
forth below, and furthermore with respect to those claims which are
appended herewith.
BRIEF DESCRIPTION OF THE DRAWINGS
[0067] FIG. 1A shows a 2-D CAD drawing of one tubular stent of the
present disclosure in longitudinally spliced and radially opened
planar view.
[0068] FIG. 1B shows an exploded top view of certain strut and
crown detail of the stent shown in FIG. 1A.
[0069] FIG. 1C shows a 3-D CAD illustration in side view of the
stent shown in FIGS. 1A and 1B.
[0070] FIG. 1D shows a photograph in side view of a portion of a
stent constructed to include similar features to the stent shown in
FIGS. 1A-C.
[0071] FIG. 2A shows a 2-D CAD drawing of another tubular stent of
the present disclosure in longitudinally spliced and radially
opened planar view.
[0072] FIG. 2B shows a 3-D CAD drawing of an exploded top view of
certain strut and crown detail of a full crown-crown cycle along a
segment of the stent shown in FIG. 2A.
[0073] FIG. 2C shows an exploded top view of a 2-D CAD drawing of
certain of the strut and crown detail of a half crown-crown cycle
along the stent shown in FIGS. 2A-B.
[0074] FIG. 2D shows a 3-D CAD illustration in side view of a stent
shown in FIGS. 2A and 2C.
[0075] FIGS. 2E-F show photographs in side view at different
respective magnifications of certain portions of a stent actually
constructed to include similar features to the stent illustrated in
FIGS. 2A-D.
[0076] FIG. 3A shows a 2-D CAD drawing of another tubular stent of
the present disclosure in longitudinally spliced and radially
opened planar view.
[0077] FIG. 3B shows a 3-D CAD illustration in angular perspective
view of a stent of similar construction to that shown in FIG.
3A.
[0078] FIGS. 3C-D show photographs in side view at different
respective magnifications of certain portions of a stent actually
constructed to include similar features to the stent illustrated in
FIGS. 3A-B.
[0079] FIG. 4 shows a 2-D CAD drawing of another tubular stent of
the present disclosure in longitudinally spliced and radially
opened planar view.
[0080] FIG. 5 shows a 2-D CAD drawing of another tubular stent of
the present disclosure in longitudinally spliced and radially
opened planar view.
[0081] FIG. 6A shows a 2-D CAD drawing of another tubular stent of
the present disclosure in longitudinally spliced and radially
opened planar view.
[0082] FIG. 6B shows a 3-D CAD illustration in angular perspective
view of a stent of similar construction to that shown in FIG.
6A.
[0083] FIGS. 6C-D show photographs in side view at different
respective magnifications of certain portions of a stent actually
constructed to include similar features to the stent illustrated in
FIGS. 6A-B.
[0084] FIG. 7A shows a 2-D CAD drawing of another tubular stent of
the present disclosure in longitudinally spliced and radially
opened planar view.
[0085] FIG. 7B shows a 3-D CAD illustration in angular perspective
view of a stent of similar construction to that shown in FIG.
7A.
[0086] FIGS. 7C-D show photographs in side view at different
respective magnifications of certain portions of a stent actually
constructed to include similar features to the stent illustrated in
FIGS. 7A-B.
[0087] FIGS. 8A-B show photographs in side view at different
respective magnifications of certain portions of another stent
constructed according to certain further aspects of the present
disclosure.
[0088] FIG. 9 shows a computer simulation of a representative
portion of a stent modeled according to one particular construction
sharing certain similar features with the stent embodiment
illustrated in FIGS. 1A-D, and as subjected to radial expansion
simulation under computer finite element analysis (FEA), and shows
shading to reflect varied levels of material strain along the
modeled structure in the simulation.
[0089] FIG. 10 shows a computer simulation of a representative
portion of another stent modeled according to one particular
construction sharing certain similar features with the stent
embodiment illustrated in FIGS. 2A-F, and as subjected to radial
expansion simulation under computer FEA, and shows shading to
reflect varied levels of material strain along the modeled
structure in the simulation.
[0090] FIG. 11 shows a computer simulation of a representative
portion of another stent modeled according to another particular
construction intended to represent certain features and
characteristics of a first commercially available stent, and as
subjected to radial expansion simulation under computer FEA, and
shows shading to reflect varied levels of material strain along the
modeled structure in the simulation.
[0091] FIG. 12 shows a computer simulation of a representative
portion of another stent modeled according to another particular
construction intended to represent certain features and
characteristics of a second commercially available stent, and as
subjected to radial expansion simulation under computer FEA, and
shows shading to reflect varied levels of material strain along the
modeled structure in the simulation.
[0092] FIG. 13 shows a computer simulation of another
representative portion of two adjacent segments of a similar stent
model as that shown in FIG. 9, and modeled according to one
particular construction sharing certain similar features with the
stent embodiment illustrated in FIGS. 1A-D, although as subjected
to a different lateral bending simulation under computer FEA, and
shows shading to reflect varied levels of material strain along the
modeled structure in the simulation.
[0093] FIG. 14 shows a computer simulation of another
representative portion of two adjacent segments of a similar stent
model as that shown in FIG. 10, and modeled according to one
particular construction sharing certain similar features with the
stent embodiment illustrated in FIGS. 2A-F, although as subjected
to a different lateral bending simulation under computer FEA, and
shows shading to reflect varied levels of material strain along the
modeled structure in the simulation.
[0094] FIG. 15 shows a computer simulation of another
representative portion of two adjacent segments of another stent
modeled to include certain features similar to those of each of the
stents modeled in FIGS. 9-10 and 13-14, and similar to the
embodiments illustrated in FIGS. 1A-D and FIGS. 2A-F, as subjected
to a different lateral bending simulation under computer FEA, and
shows shading to reflect varied levels of material strain along the
modeled structure in the simulation.
[0095] FIG. 16 shows a computer simulation of another
representative portion of two adjacent segments of a similar stent
model as that shown in FIG. 11 and intended to represent certain
aspects of a first commercially available stent, although as
subjected to a different lateral bending simulation under computer
FEA, and shows shading to reflect varied levels of material strain
along the modeled structure in the simulation.
[0096] FIG. 17 shows a computer simulation of another
representative portion of two adjacent segments of a similar stent
model as that shown in FIG. 12 and intended to represent certain
aspects of a second commercially available stent, although as
subjected to a different lateral bending simulation under computer
FEA, and shows shading to reflect varied levels of material strain
along the modeled structure in the simulation.
[0097] FIG. 18 shows a graph comparing percent restenosis results
for two different stent implants according to a pre-clinical 28 day
chronic implant study performed.
DETAILED DESCRIPTION OF THE INVENTION
[0098] The present invention provides methods and devices
associated with certain stents that are considered to provide
certain particular benefits in view of prior disclosures and
devices previously used. Certain stents of the present disclosure
are believed to present significant benefit in most "front-line"
frequent intended uses, including most cases presenting specific
challenges. Others include those which are individually and
collectively useful at particular treatment sites requiring, or at
least benefiting from, stents with particular characteristics.
Certain of the present stents adopt certain specific
characteristics considered of particular use in one or more unique
circumstances. However, while certain such characteristics may be
particularly attributed to one particular stent embodiment as
herein shown and described, it is contemplated that various
combinations between the present embodiments are also contemplated
within the scope of the present disclosure though not specifically
hereunder shown or described, as would be apparent to one of
ordinary skill.
[0099] It is appreciated that, while a particular design feature or
characteristic may vary between stents, such may also vary even
within a stent itself, such as for example along the length of the
stent. In one particular regard, stents of one significant type
contemplated hereunder are most typically constructed of repeating
or otherwise series of adjacent expandable scaffold "sections"
along a length. These sections circumferentially surround a
longitudinal bore around which they are expandable to maintain a
patent lumen when implanted along a body lumen wall. Adjacent
sections of stents are maintained in a particular spatial
relationship relative to each other during use by crossovers (in
which case the material between sections is continuous), connectors
(discrete members connecting adjacent sections) or by weld or
fusion points (hereinafter "weld points"). These terms are
collectively referred to as "connections." Different
characteristics along the length of a stent are created in
accordance with certain teachings of the present disclosure by
varying the number of connections between adjacent sections of a
stent.
[0100] As used herein, the proximal and distal ends of a stent are
to be interpreted as relative to each other and in relation to the
distal end of the catheter that delivers the stent to a treatment
site. Specifically, the distal end of the stent is closer to the
distal end of the delivery catheter than the proximal end is.
[0101] Further to the particular present stent embodiments shown
and described, these most frequently feature circumferential
sinusoidal or serpentine patterns for each stent section. According
to certain such embodiments, each section includes a
circumferentially spaced series of proximal and distal "crowns"
that include peaks of bends in the stent scaffold filament
material. These are typically formed integral with struts that
extend between and connect each distal crown to a proximal crown
according to certain particular beneficial embodiments.
[0102] In general, a filament transitions from a strut section to a
crown section (e.g. a crown portion begins) at a region where the
radius of the bend begins. For example, in the case of a simple
focal bend or elbow in a relatively constant sized filament (e.g.
regarding one or both of width, thickness, etc. for example), the
crown begins (e.g. following along the axis of a filament bridging
between crowns) when the trajectory of the filament begins to curve
or converge toward a crown "peak", which is defined as the
inflection where the filament's trajectory reverses direction
relative to the longitudinal axis of the stent. Moreover, certain
crowns may also include more complex geometry than a simple focal
elbow, yet nonetheless result in some fashion in a peak where the
shaped filament reverses its longitudinal trajectory or direction.
In particular, some crowns include multiple different radii of
curvature at different regions. In one such particular approach,
one or both of two converging struts on either side of a crown may
be radiused at one or more locations to instead provide a
transitionary divergence between the struts over a transition
region prior to inflecting again with another radiused curvature or
bend to again converge to ultimately meet along what is typically a
continuous filamental pattern through the crown region. This
multiple radiused crown pattern provides one example of an
"enlarged" crown, with two opposite shoulders providing the
transition regions with the two adjacent struts coupled to the
crown, and with adjacent struts diverging to an increased width
across the shoulders between the struts and the crown peak.
[0103] Of particular benefit in further embodiments, these struts
and crowns are formed integrally from one continuous piece of
material. In still further beneficial embodiments, the overall
stent including struts, crowns, and connections is formed from one
integral piece of material, such as for example as a laser cut or
etched tube or other piece of workpiece material processed into the
patterned tubular structure.
[0104] Stents constructed according to the present disclosure may
be made from various different types of materials as may be
apparent by one of ordinary skill. However, certain particular
examples considered to provide particularly beneficial use include
stainless steel, cobalt chromium, and nickel-titanium alloys (the
former two being generally balloon expandable, the latter being
generally self-expanding either by superelastic material recovery
or heat induced shape memory). Of the balloon expandable type, a
cobalt-chromium of the L-605 alloy type has been observed to
provide particular benefit, e.g. as provided by experiments
conducted with physical embodiments, e.g. as provided in
preclinical implant studies in the Examples of this disclosure.
However, as noted, other alloys may be chosen to suit a particular
purpose or intended use. In addition, as noted, stents per the
present embodiments may be either balloon expandable, or
self-expandable.
[0105] The specific detailed embodiments herein shown and described
are generally described in terms of balloon expandable types for
purpose of providing a complete and thorough illustration of such
family, which is generally prevalent in coronary interventions
(though also predominant or at least a present approach in other
areas of the body). The balloon expandable type of stent obviously
includes a balloon catheter type of delivery system, which
typically tracks over a guidewire to a location for stenting
(though some approaches may integrate a guidewire either in fixed
fashion or limited relative motion with the catheter). The
self-expanding type will often employ an outer retention sheath
that holds the stent in radially collapsed deflected condition from
a memory condition that is radially expanded. By removing the outer
sheath, the stent deploys under material memory recovery for
"self-expansion." It is to be appreciated that in either case,
balloon dilatation may be performed adjunctively to stenting, e.g.
either before, during, or after stent implantation. In addition,
the present stent embodiments may also be combined with other
therapies though with intended synergistic combination effect. One
such example is atherectomy of a lesion adjunctive to stenting,
and/or use of embolic filters in combination with stenting, and/or
certain diagnostic or imaging devices or methods such as
interventional vascular ultrasound (IVUS) or angiography.
[0106] For purpose of the present embodiments as shown and
described variously by reference to the Figures, adjacent stent
segments or sections are given reference numbers in sequential
order starting at 1 on the left side of the drawings shown, and
then increasing by integers referencing each next adjacent section
to the right in the Figure. Certain stent designs shown include
"peak-to-peak" (also referred to as "crown-to-crown") designs,
wherein a distal facing crown peak of one section faces or
confronts a proximal facing crown peak of the adjacent section,
though a gap or space may remain between the facing peaks. For
purposes of identifying where crossovers or connections are
provided at these confronting peak areas, a position along the
length of the stent (e.g. interface between two sections) and
location circumferentially along that position (e.g. peak-to-peak
interface) are given numbered reference designations by certain
conventions shared among the Figures as follows.
[0107] The designations for sequential stent segments or sections
start at the first section designated as 1 on the left in a Figure
as section 1, whereas the first designated position 1 for
cross-overs or connections is the first section-section interface
from the left, each designation increasing by sequential integers
toward the right in the respective Figure.
[0108] The convention for designating the relative location of
crowns in a particular segment or section begins at the first crown
designated as 1 at the uppermost area at the top of the respective
Figure, and increasing by sequential integers at each next crown
peak moving downward toward the bottom of the drawing. Where a
Figure shows a tubular stent drawn in planar view (e.g. CAD
drawings, such as FIGS. 1A, 2A, 3A, 4, 5, 6A, and 7A, that are
planar representing longitudinal splice along the stent that is
filleted open on the page), the tubular result is provided by
folding the planar view back together around the longitudinal axis
with the top lateral edge of the drawing meeting the bottom lateral
edge of the drawing. The transverse height transverse to the
longitudinal axis in such planar views thus represents the
circumference of the tubular stent. Such planar stent illustrations
at certain sections will bisect certain crown peaks such that one
half of the crown peak is at the upper edge and other half is at
the lower edge of the drawing. Where this occurs at a confronting
crown peak area, the convention reference numbering begins at the
top of the drawing where the confronting crown peaks are shown in
bisected form.
[0109] Accordingly, for serpentine designs as described, the top
most crown is designated as location 1, the next crown downward
(typically pointing in opposite direction to the crown at location
1) is designated as location 2. Further to this convention, each
distal facing crown in a segment is thus separated from the next
distal facing crown bin the same segment y two integers, as the
intervening integer designation is given to the opposite facing
crown between them, which progresses similarly for proximal facing
crowns.
[0110] For further understanding, an "X crown" description provided
for a particular stent embodiment hereunder represents X number of
full cycles of an undulating pattern per segment, thus X crowns in
a particular direction per segment, e.g. for a sinusoidal pattern
for example. According to this convention, a stent described as an
"X crown" design thus actually includes 2X crowns total, or X
crowns in each of two directions, over the entire undulating
pattern of distal and proximal facing crowns in a segment. For
still further illustration, a "10 crown" design designates 10 full
cycles of undulating pattern per segment, such as 10 proximal and
10 distal facing crowns for 20 total crowns in a segment.
[0111] The present invention is considered of particular benefit
when applied according to the teachings of the more particular
embodiments herein shown and described. However, the various
aspects, modes, embodiments, and features herein presented are also
considered applicable to these and other previously disclosed or
known stent designs to the extent such may be readily modified or
adapted consistent with the present embodiments according to one of
ordinary skill upon review of this disclosure. U.S. Pat. Nos.
5,292,331 and 5,135,536 to Boneau and Hilstead respectively, and
the references cited therein, are herein incorporated in their
entirety by reference hereto. It will be readily apparent from the
following discussion of several exemplary designs how the various
beneficial aspects of the present disclosure can be applied broadly
across a wide spectrum of such other aspects of stent
constructions, including in ways that provide beneficial results
not otherwise readily apparent or to be expected without the
benefit of the present disclosure.
[0112] The sections of the stents of the present invention can have
more or less undulations within a section or more or less sections
overall than provided by the specific illustrative examples herein
shown. However, it is nonetheless appreciated that various of the
detailed features, and their combinations, as herein specifically
shown are considered to provide particular benefit, and in any case
sufficiently exemplify certain broader aspects herein contemplated
as present invention.
[0113] As used herein, "open designs" have fewer connections
between adjacent sections and thus create a more flexible area of
the stent. Closed designs of the present disclosure have more
connections between adjacent sections and thus create a less
flexible, more supportive area of the stent. Thus, the number of
connections is varied to create particular characteristics at
different portions of the stent. The terms "open" and "closed" are
to be interpreted as relative to each other within a particular
stent, unless otherwise specifically stated. Thus, a portion of a
stent that is described as closed in one stent may be "open" when
compared to a more closed portion of a different stent. Such
reference labels are thus not appropriately to be applied as
between different stents, unless otherwise so stated, and thus the
exemplary "closed" portion of a stent as typically used hereunder
is defined as such when compared to other portions of the same
stent.
[0114] Further, a transition from open to closed or vice versa need
not be uniform as progressing along the length of the stent, but
instead can consist of progressions of a more general nature. For
example, in a stent comprising a maximum of six crossovers between
each section, a progression from open to closed may progress as (in
number of connectors between adjacent sections): 1, 1, 2, 2, 3, 3,
4, 4, 5, 5, 6, 6. This progression could also include, however,
progressions such as, without limitation, 1, 2, 1, 3, 2, 4, 3, 4,
5, 6, 5, 6 or 2, 1, 3, 1, 2, 4, 3, 5, 6, 4, 6, 5. Phrases such as
"connector position" or "crossover position" refer to the portions
of a stent between sections or at the intersection of sections
wherein there is an opportunity to provide or modify the number of
connections.
[0115] Notwithstanding the foregoing, certain particularly
beneficial stents of the present disclosure are variously shown and
described in more detail by reference to the illustrative Figures
herein shown as follows. While individual Figures and series of
related Figures will be further described in specific detail
further below, it is to be appreciated that certain specific
variations of numbers and lengths or amplitudes of stent sections,
number and locations of crowns per section, and number and
locations of crossovers between sections are represented among the
Figures on the whole.
[0116] More specifically, FIGS. 1A, 2A, 3A, 4, 5, 6A, and 7A are
respective computer aided design (CAD) drawings of stents that
represent certain specific embodiments of the present disclosure.
The particular number of sections, number of crowns per section,
and number and location of crossovers at each section-section
position along the stents for each of these particular embodiments
are shown in Table 1. In this regard, the term "position" reflects
the section-section interface along the length of the stent where
the respective cross-over(s) are identified, and the term
"location" reflects the designated peak region where the crossovers
are located at a given position. The number of crossovers at a
position are shown first, whereas their respective locations at
that position are shown parenthetically in Table 1.
[0117] As should be apparent from Table 1, certain particular
features and combinations thereof are herein contemplated,
including without limitation with respect to, for example: number
of sections along a stent length, number of crowns per section, and
number and locations of cross-overs or connections between sections
at each section-section position. While certain of these particular
embodiments are considered of particular benefit, it is nonetheless
still to be appreciated that certain broad aspects of the present
disclosure need not be necessarily limited to such specific
features in order to still provide beneficial uses. A variety of
different designs can provide suitable further embodiments of such
broad aspects of the present disclosure, though not specifically
shown here in the detailed embodiments.
[0118] For example, as a guideline to certain particular modes
herein presented, in order to determine whether a particular stent
adopts a closed-open-closed design, as elsewhere herein further
described, the stent could be divided into three equal portions
(i.e. same number of crossover positions). If the number of
crossovers, connectors or weld points is counted in each portion,
each closed end portion should individually have at least one more
crossover, connector or weld point than the middle open portion.
The closed end portions need not have the same number of
crossovers, connectors or weld points. Alternatively, to determine
if a stent is a closed-open-closed design, a stent could be divided
into two end portions, whose number of crossover positions together
is the same or different from the number of crossover positions of
the middle open portion. With this method, regardless of its size,
each closed end portion should have a greater percentage of
connections compared to the percentage of connections found within
the open middle portion. Percentage refers to the actual number of
connections compared to the spaces for possible connections.
[0119] As stated elsewhere hereunder, stents adopting a
closed-open-closed design are considered particularly useful for
treatment areas that include a vessel branch or bifurcation,
assuming the open middle portion is sufficiently "open" to provide
the various benefits considered helpful to such applications. In
one regard, the open middle portion provides for greater
flexibility at the irregular shape of the branch or bifurcation. If
the open middle portion gates a side branch or one side of a vessel
bifurcation, the open configuration may also be opened further
through balloon inflation to promote blood flow to the gated
vessel. In addition to having an open middle portion, in one
embodiment, this stent design can also include longer stent
sections in the middle of the stent which could increase the
flexibility of this portion of the stent further. Finally, a second
stent could be deployed through the open middle portion into the
second vessel stemming from the branch or bifurcation. The closed
ends of this stent design may also provide additional support for
the vessel on both sides of the flexible and open center.
[0120] However, it is also to be appreciated that a
"closed-open-closed" design, to the extent described as such
relative to its own sections, may provide particular performance
benefits beyond those just described, especially when compared
instead to stents of other designs. In one particular regard, a
stent that is considered "closed-open-closed" because its ends have
more connections or cross-overs than its middle section may
nonetheless still have greater flexibility at its ends, and perhaps
improved trackability, when compared against another stent which is
otherwise considered an "open-closed-open" design. This is the
case, for example, when a first "closed-open-closed" stent, having
three cross-overs between the terminal sections at its proximal and
distal ends versus two cross-overs between the middle sections, is
compared against a second "open-closed-open" stent design, having
for example four cross-overs between terminal sections at its
proximal and distal ends versus six cross-overs between its middle
sections. Even though the second open-closed-open design has fewer
crossovers at its ends than its middle portion, its ends
nonetheless have more cross-overs and thus more closed-cell design
than the ends of the first stent otherwise labeled
"closed-open-closed". Thus, assuming all other design features of
the stents being equivalent in this example, other than their
respective cross-over numbers and locations, the first stent may be
more flexible, and more trackable, at its ends than the second.
[0121] Further detailed aspects of the present embodiments shown in
the Figures are described as follows.
[0122] FIG. 1A shows a stent 20 which is tubular (but shown in
planar view) with a series of n=18 sections 22 arranged in series
along a length L relative to a longitudinal axis. A transverse axis
T represents the circumference of the stent 20 for the degree of
expansion shown, represents circumference if upper and lower edges
of the Figure were brought together to configure stent 20 shown in
planar view instead into a tube. The sections or segments 22 each
have an undulating pattern with a "10 crown" design per section,
meaning for example having 10 proximal facing crowns, and 10 distal
facing crowns as "valleys" between the first proximal crowns. A
full or 360 degree cycle 38 of the undulating crown pattern shown
represents a distance between similarly situated peaks (e.g. two
adjacent distal facing peaks along the axis T of the segment),
whereas a 1/2 or 180 degree cycle would reflect a portion between
adjacent proximal and distal peaks in the pattern. Extending
between the proximal and distal facing crowns are struts, such as
for example at struts 24 between opposite facing crowns 26,28 as
shown in FIG. 1A. The overall pattern for the interconnected
network of scaffold material shown for stent 20 further includes
cross-overs 30 between certain peak-to-peak interfaces between
adjacent segments, as described hereunder in further detail by
reference to FIG. 1A in Table 1. The overall segment amplitude 32
is shown between opposite facing peaks of adjacent proximal and
distal crowns 26,28. Except where crossovers are located, gaps 34
are shown between facing peaks of adjacent segments. This allows
for a range of compression between adjacent segments during flexure
of the overall stent 20, such as when crimped onto a balloon and
tracked through bends over a guidewire, for example. According to
this consideration, a complete segment length 36 is considered the
amplitude 32 of the segment crown-crown distance plus this gap 34
to the next adjacent segment or section.
[0123] In addition, FIG. 1A shows the segment crowns to include a
crown width 46, which though shown in one condition may change its
value over ranges of radial stent expansion and as designated in
the illustration by the magnitude of its circumference depicted in
planar sectioned view along transverse axis T. The cross-over areas
30 are also shown to include a width 40. It is to be appreciated
that changes in the number, relative locations, and widths 40 of
these crossovers 30 may affect the performance of stent 20, as will
variations of these features as taken in combination with other
features provided by the stent. This will be further developed with
respect to other embodiments below.
[0124] FIG. 1B shows further detail of an exploded 1/2 cycle
portion of a stent segment as follows. According to this detail
shown, varied widths across the scaffold filament are shown, for
example at width 48 at the peaks of crown 26 (and similar at
opposite facing adjacent crown 28 as shown), and at strut 24.
[0125] Moreover, a transition region of varied width exists between
the relatively constant width portion of strut 24, with variously
located radii along opposite top and bottom edges bordering the
filament (relative to the drawing on the page), such as shown at
one radiused region 52 on one edge surface (toward top of page in
drawing) and second radiused region 50 on the opposite edge
surface. The locations of these radiused regions 50,52 are slightly
varied along the filament, and in such a manner at each end (right
and left on page), such that a relatively constant straight portion
along one edge of the filament at strut 24 is provided on each
upper and lower edge, but are slightly staggered along the strut
24. This is shown for example at region 54 which is relatively
constant straight at one edge of the strut over the distance shown,
and whereas the relatively constant straight region opposite that
edge may have substantially similar distance but is staggered to
terminate about at 50 where the respective radiused region at that
edge begins. In addition, it is apparent in FIG. 1B that the radii
along the strut-crown transition region have centers of curvatures
that, while at different locations, are located in a similar
direction relative to the stent (e.g. the curves are in a similar
direction, though of different magnitudes and centers). These radii
of curvature are in different direction (e.g. outward) relative to
the radius of curvature of the outer and inner edges of crown 26,
such as shown for example at outer crown radius 49.
[0126] According to this arrangement shown in FIG. 1B and just
described, the filament width has a desirable transition of
mechanical properties as the strut 24 transitions into the
respective crowns 26,28 at either of its ends. Among other
benefits, this particular transition arrangement provides for a
transitioning stiffness in the transverse or circumferential plane
T for controlled distribution of strain during radial compression
or expansion of the respective stent 20. Additional benefit is also
provided via certain enhanced flexibility provided at the
transition region during lateral bending of the stent, such as for
example when it is tracked through bends when compressed or "rolled
down" during delivery, or through a range of mechanical bending
that may be experienced when expanded and implanted.
[0127] For further illustration of a stent assembly such as just
described by reference to the CAD animations shown in FIGS. 1A-B,
FIG. 1C shows a CAD animation of stent 20 as simulated in
3-Dimensional tubular form. The condition for stent 20 shown in
FIG. 1C is simulated to represent the overall structure as it would
generally appear if "as cut" from a solid tube. For still further
illustration, FIG. 1D shows a picture of an actual commercial
embodiment example for a stent 20 incorporating similar features as
those shown and described by reference to FIGS. 1A-C. In this
particular picture, the stent is cut from a cobalt-chromium alloy
tube, and subsequently electropolished.
[0128] The illustrative embodiment just described by reference to
FIGS. 1A-D may be constructed of varied materials, and with varied
particular dimensions, without departing from the broad aspects
herein contemplated. However, for purpose of illustration, one
particular construction exemplified by the physical embodiment
shown in FIG. 1D is considered suitable, and of particular benefit,
as follows. The stent intended to have 10 crowns/segment, 18
segments total, and about 1.0 mm segment length as illustrated for
the current embodiment, is cut from cobalt-chromium alloy tubing. A
cobalt-chromium tubing having "L605" alloy characteristics, 0.073
inch O.D./0.065 inch I.D. is used according to the present example.
The laser cutting is conducted according to typical, suitable
equipment and techniques, following two-dimensional CAD drawing
provide, such as is shown in FIGS. 1A and 1B, and to achieve about
the following dimensions by reference to those drawings (inches;
post-cutting, but before post-processing such as electropolishing):
overall length L=0.7170; transverse circumference T: 0.2300; crown
overall width 46: 0.0110; crown-to-crown inter-segment spacing 34:
0.0030; segment amplitude (including spacing) 36: 0.0400;
crown-to-crown period distance 0.0230; maximum strut width (at
constant width portion) 54: 0.0042; length of constant straight
edge section of strut 54: 0.0160; crown peak filament width 48:
0.0032; radius 50: 0.0055; radius 52: 0.0200; radius 49:
0.0055.
[0129] After cutting a stent as just described, it is subsequently
treated in standard fashion, including electropolishing, etc. A
post-processing stent filament thickness in the radial plane of
between about 0.0025 inch to about 0.0031 inch thick is believed to
provide particular benefit in the overall design. Such a stent is
then prepared for integration together with a delivery assembly
(e.g. crimping onto a balloon), packaging, sterilization, shipping,
and for subsequent use.
[0130] While the embodiment just shown and described by reference
to FIGS. 1A-D is considered to provide certain particular benefits,
FIGS. 2A-E show various illustrations representing a stent 70
providing a further embodiment of the present disclosure, and
considered to add certain particular value-added beneficial
improvements over previously disclosed designs.
[0131] More specifically, as shown in FIGS. 2A, stent 70 shares
certain features with stent 20 of FIGS. 1A-D, namely a "10 crown"
design of 18 segments 72 over a length L, and of similar
circumference along transverse axis T. Each segment 72 includes an
undulating peak-valley-peak design bridged by struts, such as shown
at strut 74 between opposite facing crowns 76,78. Each segment has
a peak-peak amplitude 82, with a period 88 between adjacent
similarly oriented peaks. The respective central strut width is
shown at 84, with primary peak width shown at 86, in FIG. 2A.
However, it is noted that the filament width according to the
present embodiment varies in certain particular regards considered
to provide certain particular benefits, as further herein described
by reference to finer details of such features, such as by
reference to FIGS. 2B-C.
[0132] FIGS. 2B-C provide exploded views of certain finer detail
regarding the strut and crown features of stent 70, and which vary
in certain regards from prior stents previously disclosed. In one
particular regard, the use of radiused edges is more extensive, and
thus a transitioning of filament geometry between struts and crowns
is more exaggerated (with area of constant strut width conversely
much more abbreviated), in the embodiment of stent 70 featured in
FIGS. 2A-E versus prior disclosures or embodiments above. More
specifically, radiused edges 98,99, while still slightly staggered
in a similar manner described by reference to FIG. 1B, extend over
a longer extended region along the filament. As a result of
extended radiused regions of strut-crown transition, the opposite
edges 96,98 strut 74 feature constant straight regions 92,94 that
are significantly shorter than in prior designs (including vs.
stent 20 in FIGS. 1A-D). The region of overlap between these
constant surfaces 92,94 also spans very little of the distance
along strut 74 between opposite facing crowns. As a result, stent
70 features a substantially abbreviated region of constant width
along the respective strut 74, shown at width 84 (which may
approach zero in certain further embodiments), with tapering
transition along the radiused edges 98,99 toward a minimum filament
width 100 at the transition region approaching the respective
crown.
[0133] This arrangement results in several highly desirable
characteristics considered to enhance certain performance aspects
of the respective stent. In one regard, a desirable distribution of
stress and strain is experienced by virtue of the various tapers
and transition region. By providing such improved transitioning,
stent performance may be enhanced, including where certain
trade-offs are frequently encountered, such as for example with
regards to lateral flexibility and radial strength. Moreover,
enhanced distribution of stress/strain during expansion and wear is
considered a distinct benefit, including for example and in
particular in setting of coated stents, such as drug eluting
stents. In this latter regard, more typical conventional designs
that distribute expansion strain across one focal crown peak region
have been observed to result in compromised coating integrity. The
current embodiment provides for a bifurcation of that strain to the
two tapered transition regions at the crown shoulders for
beneficially modified distribution of material strain from flexure
or expansion. This is considered to present a particular
enhancement for maintaining surface coating integrity. Accordingly,
the present embodiments further contemplate inclusion of various
surface coatings on the stent, and drug elution therefrom.
[0134] The present embodiment also features a particular crown
design also considered to provide particular benefit, including in
particular combination with other features provided by the
embodiment. More specifically, as shown in FIGS. 2B-C, Crown 76
includes an inner radius 83 that is less than outer radius 85.
Spacing 87 shown in FIG. 2C represents the separation between
centers of outer radius 85 (located at end of line on right side of
spacing in the Figure) and inner radius 83 (located at end of line
on left side of spacing in the figure). The crown is generally
defined as the arcuate region between inflection points from these
inner and outer crown radii 83,85 and transition region radii
98,99. As a result of the overall geometry of such crowns, the
largest width portion 86 of the crown region is at the peak (such
as shown by location of reference arrows for the radii 83,89 in
FIG. 2B). The crown width transitions from this maximum width at
the peak to gradually narrowing width toward the sides of the crown
and into the transition region of narrowed width 100. This crown
geometry is considered to provide certain further distinct benefits
with respect to certain particular stent performance
characteristics, including in particular with respect to
stress/strain distribution along the stent and resulting mechanical
characteristics during circumferential deformation, such as during
radial crimping for delivery and radial expansion for implantation.
This is further illustrated elsewhere in the present disclosure and
by favorable comparison against other exemplary stents previously
introduced and having experienced substantial commercialization and
clinical use.
[0135] Certain beneficial features of the present embodiment shown
in FIG. 2A are thus herein shown and described with respect to
certain strut and crown details of the embodiment, such as for
example as just illustrated above by reference to FIGS. 2B-C.
However, other benefits are also provided by the present
embodiment, as further shown and described by reference to FIGS.
2D-F as follows.
[0136] In particular, as shown in FIG. 2D (and by further reference
to similarly constructed commercial embodiment examples shown in
FIGS. 2E-F), stent 70 includes a series of crossovers 80 that
differ from prior cross-overs and connectors previously described.
Such difference is considered to provide certain particular
benefits, especially when considered in combination with other
beneficial features provided by the embodiment as elsewhere herein
described. More specifically, cross-over 80 of stent 70 has a width
81 that is much larger than other cross-overs previously described,
and including larger than that shown for the embodiment in FIGS.
1A-D. Prior designs provide cross-overs or connectors in a manner
intended to provide certain degree of flexibility between adjacent
segments along a stent. Such conventional cross-over regions most
typically contribute a significant portion, and generally a
majority, of the lateral flexibility of the overall stent during
lateral flexure. However, according to the present embodiment,
these cross-overs of substantial width represent very little, if
any, of lateral flexure to the stent. This results from the
substantial width given to the cross-overs relative to the
remaining portions of the stent (e.g. crowns, struts, and
transition regions) all generally including smaller widths and thus
less stiffness and more flexibility than the cross-overs. In
particular, the tapering filament width along the extended
transition region from struts to crowns within each stent segment,
as noted above, flexibly absorb more flexure than experienced
within the segments under other prior designs, and, as noted above,
more than is experienced at the present stent's own cross-over.
[0137] The illustrative embodiment just described by reference to
FIGS. 2A-D may be constructed of varied materials, and with varied
particular dimensions, without departing from the broad aspects
herein contemplated. However, for purpose of illustration, one
particular construction exemplified by the physical embodiment
shown in FIG. 2C-D is considered suitable, and of particular
benefit, as follows. The stent intended to have 10 crowns/segment,
18 segments total, and about 1.0 mm segment length as illustrated
for the current embodiment, is cut from cobalt-chromium alloy
tubing. A cobalt-chromium tubing having "L605" alloy
characteristics, 0.073 inch O.D./0.065 inch I.D. is used according
to the present example. The laser cutting is conducted according to
typical, suitable equipment and techniques, following
two-dimensional CAD drawing provide, such as is shown in FIGS. 2A
and 2C, and to achieve about the following dimensions by reference
to those drawings (inches; post-cutting, but before post-processing
such as electropolishing): overall length L=0.7170; transverse
circumference T: 0.2300; crown overall width 89: 0.0110;
crown-to-crown inter-segment spacing: 0.0030; segment amplitude
(including spacing) 82: 0.0400; crown-to-crown period distance 88:
0.0230; maximum strut width (at constant width portion) 84: 0.0045;
minimum width at transition region 100: 0.0031; length of constant
straight edge section of strut 94: 0.0050; crown peak filament
width 86: 0.0047; distance between centers of inner radius 83 and
outer radius 85: 0.0015; inner radius 83: 0.0023; outer radius 85:
0.0055; radius 98: 0.0250; radius 99: 0.0150.
[0138] The specific geometries and dimensions for crossover 80 may
vary and to suit a particular application or adaptation of other
intercooperating elements in the stent 70. However, for the
illustrative embodiment shown, the cross-over extends over a length
generally representing the gap distance or spacing between adjacent
facing crowns of adjacent segments, and is slightly radiused on
each upper and lower edge. In this regard, further to the detailed
description provided above for an exemplary physical embodiment,
the crossover may have about the following dimensions (inches):
outer radius of cross-over: 0.0055; cross-over width (at minimum
dimension) 81: 0.0060.
[0139] After cutting a stent as just described, it is subsequently
treated in standard fashion, including electropolishing, etc. to
construct a particularly beneficial stent according to the present
embodiment, with similar dimensions as noted above (generally
slightly reduced from electropolishing and post-processing after
laser cutting). A post-processing stent filament thickness in the
radial plane of between about 0.0028 inches is believed to provide
particular benefit in the overall design. Such a stent is then
prepared for integration together with a delivery assembly (e.g.
crimping onto a balloon), packaging, sterilization, shipping, and
for subsequent use.
[0140] According to the foregoing, it is clear that the present
embodiment is considered to provide certain specific benefits
arising from particular features shown and described. It is also to
be made clear, however, that the current disclosure broadly
contemplates substantial benefit afforded by certain broad aspects
illustrated by the embodiments. These aspects are not necessarily
to be limited by each specific feature provided in showing and
describing the embodiments (though such may provide additional
substantial benefit).
[0141] For example, one such broadly contemplated aspect provides a
stent with serial expandable segments, interconnected with
cross-overs or connectors, wherein the cross-overs or connectors
contribute less lateral flexibility to the stent than is
contributed within the segments themselves. According to one
particular beneficial aspect of this, the most prominent lateral
flexure is experienced along narrowed region of the struts, and a
particular benefit is considered by providing this along a tapering
region of transition between struts and crowns within a segment.
These aspects and modes are considered unique to prior designs, as
are further more detailed aspects such as providing the widest
and/or stiffest portion of a strut-crown-crossover/connector design
at the crossover/connector. In addition, other beneficial aspects
of the present embodiment are found in the expansion
characteristics that the tapering strut-crown transition provides
in context of a crown design which has its greatest width at its
peak, with tapering narrowing along its sides. While considered a
valuable novel feature even if incorporated alone from this
disclosure into prior designs, it is also considered to provide
particular further benefit when combined with a strut-to-crown
transition that has an extended, narrowing taper from a
significantly abbreviated region of relatively constant width
between crowns, toward a minimum width at the transition region
adjacent to the crown. Staggering constant straight edge regions
and radiused regions along opposite inner and outer edges relative
to each other provides still further benefit.
[0142] It is to be further appreciated that various features, such
as certain of those just described, may relate to each other,
though may be also considered independently. For example, the
embodiment of FIG. 2 provides a crown with increased width at its
crown peak, inner and outer radii at the peak with offset relative
centers, and increased strain distribution at the crown shoulders
during radial expansion vs. at the crown peak. Each of these
features relates to the other. For example, in the particular
embodiment, the offset inner and outer radii provide one approach
to result in a wider filament at the peak than at the shoulders.
The wider filament at the peak is one approach to result in
bifurcated strain distribution at the shoulders versus at the peak.
Although these are interrelated as just described, they are not in
all cases to be considered necessarily combined as such. For
example, filament thickness in the radial plane, versus width in
the circumferential plane, may be modified in order to bifurcate
strain away from the crown peak and to the crown shoulders (even
with constant width or even potentially more narrow width at the
crown, depending on the extent of thickness variation). More
specifically, by making the crown peak thicker than the shoulders,
strain distribution may be shifted from the peak to the shoulders.
In another example, inner and outer radii of the filament at the
crown peak may be concentrically centered, yet the crown peak may
still be wider than the crown shoulders. This may be accomplished
for example by providing other combinations of radiused (or
otherwise stepped or tapered) edges at the shoulders, such as for
example vs. at the crown peak.
[0143] A closed-open-closed arrangement is provided by the
embodiment just described, and is considered beneficial. More
specifically, as elsewhere noted hereunder, the final two segments
on each stent end include four crossovers between them, whereas the
remaining intersegment positions along the stent between these ends
contain two crossovers. While other aspects represented by the
embodiment are considered broadly and accommodating of other
crossover patterns or arrangements, this specific arrangement is
considered of benefit, including without limitation in context of
its combination with other features provided by this embodiment. In
one regard, the four crossovers at each end provide sufficient
stability at the ends to prevent linear collapse between the
adjacent segments during use. The two crossovers between the other
segments between the stent ends provide more flexibility that the
four crossover region. Furthermore, the benefits of this crossover
arrangement is considered to enhance performance in view of the use
of the particular crossovers themselves of the embodiment, which
are relatively wider and stiffer than other prior crossovers or
interconnects (especially non-welded), and wider and stiffer than
the more flexible locations along the intrasegment strut-crown
transitions of this stent.
[0144] Notwithstanding the foregoing, however, it is to be
appreciated that the particular combination of crown features
provided by the current embodiment provide a particularly unique
and valuable approach with distinct improvements presented over
previously disclosed stents. Strain is distributed in a unique
bifurcated manner to transitions at the crown shoulders and away
from the crown peak. While strain of expansion and flexure are
dictated by properties at these tapered transition regions at the
crown shoulders, other areas with much lower strain contribution
are widened. This enhances visibility without compromising
performance by increasing radiopaque metal material to the low
strain to no strain regions of the stent. This also provides areas
of wider surface area to enhance local drug delivery. In contrast,
other prior stents most typically provide uniform thickness along
the filament, which is equal at focal strain regions and relatively
low strain regions, versus engineering the undulating filament with
customized features that vary along its length to maximize
effectiveness of multiple variables. These multiple variables
otherwise compete if given the same treatment at different regions.
For example, to provide a strut thickness uniformly along the
crown, it has certain constraints at the high strain region to
provide certain expansion characteristics. Limiting the strut to
the same constrained geometry at low strain regions compromises
other performance features, such as for example radiopacity and
surface area for enhanced local drug delivery.
[0145] In any case, these broad aspects contemplated within the
present disclosure are to be considered of particular individual
value, and without necessarily requiring their limitation by
further more detailed features of embodiments herein specifically
shown and described, though such more particular details are
considered to present still further substantial benefit.
[0146] It is specifically contemplated that certain detailed
aspects of the prior embodiments introduced above may be modified
to suit a particular purpose, without departing from the broader
aspects herein disclosed. For example, as shown in FIGS. 3A-6D, the
particular number of crowns in a segment, or number of segments
along a length of an overall stent, may be varied from those
aspects shown for the specific embodiment in FIGS. 2A-2F above, but
while preserving the various particularly beneficial features
described for that specific embodiment.
[0147] In particular, FIGS. 3A-D illustrate a stent 110 that
includes similar features with respect to crown, strut,
transitioning region, and crossover design as noted for FIGS. 2A-F,
but provides this combination of features in a "9 crown" per
segment design versus the "10 crown" per segment design of the
prior embodiment.
[0148] The illustrative embodiment just described by reference to
FIGS. 3A-D may be constructed of varied materials, and with varied
particular dimensions, without departing from the broad aspects
herein contemplated. However, for purpose of illustration, one
particular construction exemplified by the physical embodiment
shown in FIG. 2C-D is considered suitable, and of particular
benefit, as follows. The stent intended to have 9 crowns/segment,
18 segments total, and about 1.2 mm segment length as illustrated
for the current embodiment, is cut from cobalt-chromium alloy
tubing. A cobalt-chromium tubing having L605 alloy characteristics,
0.073 O.D./0.065 I.D. is used according to the present example. The
laser cutting is conducted according to typical, suitable equipment
and techniques, following two-dimensional CAD drawing provide, such
as is shown in FIG. 3A, and to achieve about the following
dimensions (inches; post-cutting, but before post-processing such
as electropolishing): overall length L=0.7160; transverse
circumference T: 0.2340; crown overall width: 0.0110;
crown-to-crown inter-segment spacing: 0.0040; segment amplitude
(including spacing): 0.0480; crown-to-crown period distance:
0.0260; maximum strut width (at constant width portion): 0.0045;
minimum width at transition region: 0.0031; length of constant
straight edge section of strut: 0.0075; crown peak filament width:
0.0047; distance between centers of crown inner radius and outer
radius: 0.0015; inner radius: 0.0023; outer radius: 0.0055; larger
strut transition region radius: 0.0250; smaller strut transition
region radius: 0.0150.
[0149] The specific geometries and dimensions for the crossover per
the current embodiment may vary and to suit a particular
application or adaptation of other intercooperating elements in the
stent 110 of the present embodiment. However, for the illustrative
embodiment shown, the cross-over extends over a length generally
representing the gap distance or spacing between adjacent facing
crowns of adjacent segments, and is slightly radiused on each upper
and lower edge. In this regard, further to the detailed description
provided above for an exemplary physical embodiment, the crossover
may have about the following dimensions (inches): outer radius of
cross-over: 0.0065; cross-over width (at minimum dimension):
0.0057.
[0150] After cutting a stent as just described, it is subsequently
treated in standard fashion, including electropolishing, etc. to
construct a particularly beneficial stent according to the present
embodiment, with similar dimensions as noted above (generally
slightly reduced from electropolishing and post-processing after
laser cutting). A post-processing stent filament thickness in the
radial plane of about 0.0028 inches (e.g. .+-. about 0.0003 inches)
is believed to provide particular benefit in the overall design.
Such a stent is then prepared for integration together with a
delivery assembly (e.g. crimping onto a balloon), packaging,
sterilization, shipping, and for subsequent use.
[0151] FIG. 4 shows a stent 120 that represents an "8 crown" per
segment embodiment, and which preserving the various beneficial
featured shared between the 10 and 9-crown embodiments previously
presented above with respect to FIGS. 2A-3D.
[0152] The illustrative embodiment just described by reference to
FIG. 4 may be constructed of varied materials, and with varied
particular dimensions, without departing from the broad aspects
herein contemplated. However, for purpose of illustration, one
particular construction considered particularly suitable for
constructing a beneficially functional stent according to this
embodiment is as follows. The stent intended to have 8
crowns/segment, 18 segments total, and about 1 mm segment length as
illustrated for the current embodiment, is cut from cobalt-chromium
alloy tubing. A cobalt-chromium tubing having L605 alloy
characteristics, 0.073 O.D./0.065 I.D. is used according to the
present example. The laser cutting is conducted according to
typical, suitable equipment and techniques, following
two-dimensional CAD drawing provide, such as is shown in FIG. 4,
and to achieve about the following dimensions (inches;
post-cutting, but before post-processing such as electropolishing):
overall length L=0.7170; transverse circumference T: 0.2320; crown
overall width: 0.0110; crown-to-crown inter-segment spacing:
0.0030; segment amplitude (including spacing): 0.0400;
crown-to-crown period distance: 0.0290; maximum strut width (at
constant width portion): 0.0045; minimum width at strut-crown
transition region: 0.0031; length of constant straight edge section
of strut: 0.0050; crown peak filament width: 0.0047; distance
between centers of crown inner radius and outer radius: 0.0015;
inner radius: 0.0023; outer radius: 0.0055; larger strut transition
region radius: 0.0250; smaller strut transition region radius:
0.0150.
[0153] The specific geometries and dimensions for the crossover per
the current embodiment may vary and to suit a particular
application or adaption of other intercooperating elements in the
stent 120 of the present embodiment. However, for the illustrative
embodiment shown, the cross-over extends over a length generally
representing the gap distance or spacing between adjacent facing
crowns of adjacent segments, and is slightly radiused on each upper
and lower edge. In this regard, further to the detailed description
provided above for an exemplary physical embodiment, the crossover
may have about the following dimensions (inches): outer radius of
cross-over: 0.0055; cross-over width (at minimum dimension):
0.0060.
[0154] After cutting a stent as just described, it is subsequently
treated in standard fashion, including electropolishing, etc. to
construct a particularly beneficial stent according to the present
embodiment, with similar dimensions as noted above (generally
slightly reduced from electropolishing and post-processing after
laser cutting). A post-processing stent filament thickness in the
radial plane of between about 0.0028 inches is believed to provide
particular benefit in the overall design. Such a stent is then
prepared for integration together with a delivery assembly (e.g.
crimping onto a balloon), packaging, sterilization, shipping, and
for subsequent use.
[0155] FIG. 5 shows a stent 130 that represents a "7 crown" per
segment embodiment, and which preserving the various beneficial
features shared between the 10, 9, and 8-crown embodiments
previously presented above with respect to FIGS. 2A-4.
[0156] The illustrative embodiment just described by reference to
FIG. 5 may be constructed of varied materials, and with varied
particular dimensions, without departing from the broad aspects
herein contemplated. However, for purpose of illustration, one
particular construction considered particularly suitable for
constructing a beneficially functional physical stent of the
present embodiment is as follows. The stent intended to have 7
crowns/segment, 15 segments total, and about 1.2 mm segment length
as illustrated for the current embodiment, is cut from
cobalt-chromium alloy tubing. A cobalt-chromium tubing having L605
alloy characteristics, 0.073 O.D./0.065 I.D. is used according to
the present example. The laser cutting is conducted according to
typical, suitable equipment and techniques, following
two-dimensional CAD drawing provide, such as is shown in FIG. 5,
and to achieve about the following dimensions (inches;
post-cutting, but before post-processing such as electropolishing):
overall length L=0.7160; transverse circumference T: 0.2310; crown
overall width: 0.0110; crown-to-crown inter-segment spacing:
0.0040; segment amplitude (including spacing): 0.0480;
crown-to-crown period distance: 0.0330; maximum strut width (at
constant width portion): 0.0045; minimum width at strut-crown
transition region: 0.0031; length of constant straight edge section
of strut: 0.0075; crown peak filament width: 0.0047; distance
between centers of crown inner radius and outer radius: 0.0015;
inner radius: 0.0023; outer radius: 0.0055; larger strut transition
region radius: 0.0250; smaller strut transition region radius:
0.0150.
[0157] The specific geometries and dimensions for the crossover per
the current embodiment may vary and to suit a particular
application or adaptation of other intercooperating elements in the
stent 130 of the present embodiment. However, for the illustrative
embodiment shown, the cross-over extends over a length generally
representing the gap distance or spacing between adjacent facing
crowns of adjacent segments, and is slightly radiused on each upper
and lower edge. In this regard, further to the detailed description
provided above for an exemplary physical embodiment, the crossover
may have about the following dimensions (inches): outer radius of
cross-over: 0.0065; cross-over width (at minimum dimension):
0.0057.
[0158] After cutting a stent as just described, it is subsequently
treated in standard fashion, including electropolishing, etc. to
construct a particularly beneficial stent according to the present
embodiment, with similar dimensions as noted above (generally
slightly reduced from electropolishing and post-processing after
laser cutting). A post-processing stent filament thickness in the
radial plane of between about 0.0025 inches to about 0.0031 inches,
such as for example about 0.0028 inches, is believed to provide
particular benefit in the overall design. Such a stent is then
prepared for integration together with a delivery assembly (e.g.
crimping onto a balloon), packaging, sterilization, shipping, and
for subsequent use.
[0159] FIGS. 6A-D show a stent 140 representing a further "6 crown"
embodiment, which also preserves the various beneficial features
shared between the prior 10, 9, 8, and 7-crown embodiments
represented in FIGS. 2A-5 above. Included for still further
illustration are pictures of an exemplary physical embodiment
constructed, as shown in FIGS. 6C-D.
[0160] The illustrative embodiment just described by reference to
FIG. 6A may be constructed of varied materials, and with varied
particular dimensions, without departing from the broad aspects
herein contemplated. However, for purpose of illustration, one
particular construction considered particularly suitable for
constructing a beneficially functional physical stent of the
present embodiment is as follows. The stent intended to have 6
crowns/segment, 15 segments total, and about 1.2 mm segment length
as illustrated for the current embodiment, is cut from
cobalt-chromium alloy tubing. A cobalt-chromium tubing having
"L605" alloy characteristics, 0.073 O.D./0.065 I.D. is used
according to the present example. The laser cutting is conducted
according to typical, suitable equipment and techniques, following
two-dimensional CAD drawing provide, such as is shown in FIG. 6A,
and to achieve about the following dimensions (inches;
post-cutting, but before post-processing such as electropolishing):
overall length L=0.7160; transverse circumference T: 0.2340; crown
overall width: 0.0110; crown-to-crown inter-segment spacing:
0.0085; segment amplitude (including spacing): 0.048 crown-to-crown
period distance: 0.039; maximum strut width (at constant width
portion): 0.042; minimum width at strut-crown transition region:
0.003; length of constant straight edge section of strut: 0.010;
crown peak filament width: 0.042; distance between centers of crown
inner radius and outer radius: 0.0012; inner radius: 0.0025; outer
radius: 0.0055; larger strut transition region radius: 0.0250;
smaller strut transition region radius: 0.0150.
[0161] The specific geometries and dimensions for the crossover per
the current embodiment may vary and to suit a particular
application or adaptation of other inter-cooperating elements in
the stent 140 of the present embodiment. However, for the
illustrative embodiment shown, the cross-over extends over a length
generally representing the gap distance or spacing between adjacent
facing crowns of adjacent segments, and is slightly radiused on
each upper and lower edge. In this regard, further to the detailed
description provided above for an exemplary physical embodiment,
the crossover may have about the following dimensions (inches):
outer radius of cross-over: 0.0150; cross-over width (at minimum
dimension): 0.0060.
[0162] After cutting a stent as just described, it is subsequently
treated in standard fashion, including electropolishing, etc. to
construct a particularly beneficial stent according to the present
embodiment, with similar dimensions as noted above (generally
slightly reduced from electropolishing and post-processing after
laser cutting). A post-processing stent filament thickness in the
radial plane of between about 0.0022 inches and about 0.0035, such
as between about 0.0025 inches and about 0.0031 inches, and more
specifically about 0.0028 inches, is believed to provide particular
benefit in the overall design. Such a stent is then prepared for
integration together with a delivery assembly (e.g. crimping onto a
balloon), packaging, sterilization, shipping, and for subsequent
use.
[0163] For a stent of a given number of segments, and similar
overall length L and transverse circumference T, reducing the
number of crowns in the manner illustrated by the various
embodiments above will typically involve adjusting other geometric
aspects of the design within a segment. This may include, for
example, adjusting the strut angle between crowns, as fewer crowns
around the circumference will generally translate to further
crown-crown lateral distance between them for a given
circumference. Moreover, this also generally corresponds with an
increase in strut length to accommodate the increased spacing
between crowns across which the struts traverse.
[0164] However, such variations between crown numbers is not
necessarily intended to represent similar circumferences. For
example, the embodiments of FIGS. 2A-4 representing similar stent
designs in 8-10 crown per segment variations, respectively, may
represent suitable alternative structures for intended expanded
diameters between about 2.5 mm to about 4.5 mm, or in particular
between about 3.0 mm to about 4.0 mm, such as for intended use in
vessels requiring such sizing. Alternatively, similar stent
designs, but that represent 6-8 crown per segment variations, may
provide suitable structures for intended expanded diameters between
about 2.0 to about 3.5 mm, or in particular between about 2.0 and
3.0 mm. Accordingly, where smaller vessels are intended for
implantation, smaller expanded diameters are required of the stent
implants and thus, for achieving a target range of coverage
regarding stent filament material to vessel wall area, reduced
crown numbers may be employed for the stent segments such as
presently illustrated. In addition, varying crown numbers per
segment may accommodate changing requirements where more open, or
alternatively more closed, types of designs are desired for given
applications but at a particular circumference.
[0165] Further to the foregoing, one particular exemplary kit of
multiple stents (generally individually packaged separately for
individual use) and amongst which to choose a device to accommodate
alternative or variable sizing considerations. Illustrative
examples of such kit and considered of particular benefit for use
is as follows: 8 to 10 Crown stent for 3.5 to 4.5 mm vessel sizing;
5 to 8 crown stent for 2.5-3.5 mm vessel sizes; and 2-6 crown stent
for <2.5 mm vessel sizes. A more specific example considered
beneficial provides a 10 crown stent for 3.5 to 4.0 or 4.5 mm
vessel sizing, and 8 crown stent for 2.5 mm to 3.0 or 3.5 mm vessel
sizing. Appropriate labels are provided on each stent of the kit
indicating its respective size range for intended use. However, it
is to be appreciated that features such as crown numbers per
segment, and related lumen wall coverage of the stent, may vary
with respect to desired specifications for a particular
application. Such variations of design over sizes, and related
performance differences, will vary for example for different
intended body environments to be stented, such as for example
coronary vascular, neurovascular, renal, grafts, peripheral
vascular, and other lumens such as in lungs, urinary tract,
reproductive system, etc. The kits just described, and other
embodiments and various features of the present disclosure, may
vary between such different applications.
[0166] Accordingly, the various present aspects, modes, and
embodiments are considered broadly and not necessarily limited to a
specific kit of sizing and related design features for such sizes.
For example, a range of 6 or more crowns could be used for larger
vessels sizes of greater than 4.5 mm.
[0167] Another adjustment that may be made to accommodate reduction
of crown numbers per segment, over a fixed length, may include
reducing the number of overall segments. Moreover, other purposes
may provide similar basis to adjust the number of segments over a
length. When this is done, either or both of the length of the
retained segments, and/or the spacing between them, is adjusted to
achieve the overall length if such criteria is fixed (e.g. for a
standard 18 mm stent length). The illustrative embodiments and
examples shown in FIGS. 5-7B feature 15 segments along the
respective stent lengths, versus 18 segments of the other
embodiments of similar overall stent lengths such as shown in FIGS.
2A-4.
[0168] In addition to preserving the combination of beneficial
features of FIGS. 2A-D while varying other features such as crown
coverage in the stent segments, other features may also be varied.
It is contemplated that while the particular combination of
features shared among FIGS. 2A-6C provide significant and
complimentary benefit, each such feature taken alone may provide
benefit in certain circumstances without necessarily requiring the
other.
[0169] For example, as shown in FIGS. 7A-B, a stent 150 is provided
in a "6 crown" per segment design as similarly shown for FIGS.
6A-C, and with similar beneficial features provided along the
crowns and struts within the stent segments as shown for FIGS.
6A-C. However, in the present embodiment, an alternative cross-over
152 is shown that differs from that shown and shared among the
prior embodiments of FIGS. 2A-6C (and differing still from the
embodiment shown in FIGS. 1A-D). More specifically, crossovers 152
are of an intended "flexible" type, and include relatively thin
"U"-shaped filament of substantially reduced width compared with
the other filament portions of the stent (e.g. crowns and struts).
These "U"-shaped cross-overs are oriented in the transverse
circumferential plane T lateral to the longitudinal axis L,
allowing for the "U"-shape to flexibly expand longitudinally during
lateral bending of the stent. This overall arrangement provides the
particularly enhanced flexibility of the strut-crown transition
region of prior embodiments above, with the additional flexibility
provided at the crossovers. However, it is also apparent that the
crown segments may be further spaced to accommodate these lateral
"U"-shaped crossovers. This is readily seen by reference to stent
160 shown in FIGS. 8A-B as a physical embodiment example
constructed to incorporate similar features to the embodiment shown
in FIGS. 7A-B, but instead incorporating a "9-crown" per segment
design.
[0170] The particular stent embodiments herein shown and described
generally represent closed-open-closed approach to stent design,
though incorporating various particularly beneficial aspects
uniquely presented by the present disclosure. However, as elsewhere
herein mentioned, certain aspects of the particular exemplary
embodiments may be modified into forms other than those
specifically shown, and particular beneficial features may be
isolated from their combination with others in the present
embodiments, without departing from the broad intended scope of
various aspects herein contemplated. This includes with respect to
the closed-open-closed arrangement of the stents described. The
specific applications under this general arrangement shown in the
embodiments may be altered to suit particular needs or desires. Or,
the overall relationship of closed-open-closed within the stents
may be modified to something different, and still incorporate other
features presented by this disclosure as a distinct benefit.
[0171] One further stent herein contemplated provides an
"open-closed-open" feature variation between the proximal, mid, and
distal regions of the stent. This relationship between varied
features along the stent length provides for greater flexibility
characteristics at both ends of the stent. This feature can provide
for a less abrupt transition between stented and unstented portions
of a vessel and can also improve the deliverability of the
stent.
[0172] Another stent of the present disclosure provides a
"closed-open-closed" feature variation between the proximal, mid,
and distal stent regions. This relationship is generally
illustrated by the various present embodiments shown and described
by reference to the Figures. In addition to the other benefits of
such embodiments as elsewhere explained hereunder, this
relationship between varied features along the stent length is also
considered to be particularly beneficial for example when the area
to be treated is in the vicinity of (i.e. found before and after) a
vessel branch or bifurcation. The open middle portion of the stent
provides for greater flexibility so that the stent can conform more
readily to the irregular shape of this portion of the vessel. In
addition, when treating a vessel in an area of a vessel branch or
bifurcation, it is common for the stent to pass over the opening to
the second vessel, thereby impeding blood flow into the second
vessel (i.e. "gating" the vessel). A more open middle portion can
reduce this "gating" effect and allow for better blood flow into
the second vessel. Further, if needed, the nature of an open middle
portion allows another stent to be deployed through the open middle
portion into a gated vessel branch. Closed ends bordering the open
middle portion provide better and more uniform support on each side
of the vessel bifurcation.
[0173] Another stent herein contemplated provides a "closed-open"
feature variation along the stent length. In one particular
example, the stent is closed at its proximal end while becoming
generally more open along the length of the stent. The
"closed-open" embodiment can be advantageous when a more
deliverable (i.e. more flexible distal end), yet supported stent is
needed at a particular treatment site.
[0174] Still further, another stent herein contemplated provides an
"open-closed" feature variation along its length, wherein the stent
is open at its proximal end but is more closed distally along the
length of the stent. This design is considered advantageous for
example when the treatment site is relatively accessible (i.e. a
more deliverable stent is not required). The closed distal end of
this present stent provides uniform support while the open proximal
end allows for a less abrupt transition between stented and
unstented portions of the vessel. An open feature at the proximal
end of the stent is considered especially advantageous because this
is the area of a stented vessel that is more frequently observed to
undergo restenosis using conventional devices. A treating physician
may choose one of the various embodiments of the stents of the
present invention depending on the particular site to be treated
and the particular patient's treatment history.
[0175] As a guideline to determine whether a particular stent
adopts a closed (proximal) to open (distal) arrangement, the stent
can be divided into two equal portions (i.e. the same number of
crossover, connector or weld point positions). If the number of
crossovers, connectors or weld points is counted in each portion,
the closed proximal portion should have at least one more
crossover, connector or weld point than the open distal portion.
Alternatively, to determine if a particular stent adopts a closed
(proximal) to open (distal) design, the stent can be divided into
two portions and a percentage of actual crossovers, connectors or
weld points over possible spaces for crossovers, connectors or weld
points can be calculated. With this calculation method, the open
end of the stent would have a smaller percentage of crossovers,
connectors or weld points than the closed end. While these methods
can be done to make the determinations noted, they are not
necessarily limiting so long as the spirit of the general
descriptions and definitions are met, as would be apparent to one
of ordinary skill.
[0176] These embodiments of the present disclosure have desirable
characteristics when a particular treatment site requires a stent
with enhanced deliverability characteristics. This embodiment might
be chosen over an open-closed-open embodiment by a treating
physician when the physician determines that the added support of a
fully closed proximal end is desired at a particular treatment
site.
[0177] As a guideline to determine whether a particular stent
adopts an open (proximal) to closed (distal) embodiment of the
present disclosure, the stent can be divided into two equal
portions (i.e. the same number of crossover, connector or weld
point positions). If the number of crossovers, connectors or weld
points is counted in each portion, the open proximal portion should
have at least one less crossover, connector or weld point than the
closed distal portion. Alternatively, to determine if a particular
stent adopts an open (proximal) to closed (distal) design, the
stent can be divided into two portions and a percentage of actual
crossovers, connectors or weld points over possible spaces for
crossovers, connectors or weld points can be calculated. With this
calculation method, the open end of the stent is required to have a
smaller percentage of crossovers, connectors or weld points than
the closed end.
[0178] These embodiments of the present disclosure have desirable
characteristics when a particular treatment site is easily
accessible. The closed portion of the stent provides required
support while the open proximal end provides for a less abrupt
transition from the stented to unstented proximal portion of the
vessel. A less abrupt transition is especially advantageous at the
proximal portion of the stented vessel because it is this area of
the vessel that is otherwise most likely to suffer from
restenosis.
[0179] The stents of the present disclosure can be used in any
blood vessel, including, for example and without limitation, the
coronary vasculature (which includes, without limitation, the
right, left common, left anterior descending and circumflex
arteries and their branches) and the peripheral vasculature
(including, without limitation, branches of the carotid, aorta,
femoral, renal, popliteal, and related arteries). While the stents
of the present disclosure mainly have been described in terms of
their use in a blood vessel, they can also be used in other lumens
of the body, for example and without limitation, respiratory ducts,
gastrointestinal ducts, bile ducts, the urinary system, the
digestive tube, and the tubes of the reproductive system in both
men and women.
[0180] The stents of the present disclosure can be coated with an
appropriate material to enhance clinical performance. For instance,
various coatings can be capable of releasing a drug or bioactive
agent to assist in the repair of a diseased vessel and to assist in
the prevention, treatment or inhibition of restenosis. Further, the
stents of the present disclosure can be coated with a radiopaque
material, such as a dye or marker to allow for better positioning
during implantation. These coatings can be continuous or
discontinuous on the surface of the stents and can be disposed on
the interior and/or the exterior surface(s) of the stents. Coatings
can include one or more layers and can be coated either directly
onto the stents or onto a primer material on the stents.
[0181] A coating placed on the stents of the present disclosure
should generally be biocompatible for most intended uses, in order
to minimize adverse interaction with the walls of the vessel or
duct lumen or with the liquid flowing through the lumen. However,
some stent uses may be intended specifically to invoke a biological
response, such as for example to promote vessel closure such as for
aneurysm blockage etc. The coating may be of a durable type with
sustained presence on the implant, or may be of a dissolvable or
bioerodable type. The coating in many circumstances can consist of
a polymeric coating material.
[0182] In one embodiment of the present disclosure the polymeric
coating can have zwitterionic pendant groups, generally ammonium
phosphate ester groups, for instance phosphoryl choline groups, or
analogues thereof. Other examples of suitable polymers can be found
in published International Patent Application Publication Nos.
WO-A-93/16479 and WO-A-93/15775 which are hereby incorporated by
reference for all they contain regarding polymers and coatings.
Coatings used in accordance with the present disclosure also can
consist of nonpolymeric coating materials. The coating also can
include a metallic coating placed onto the surface of the stent
through electro- or electroless deposition processes. These may be
to provide a desired surface characteristic, or may be loaded with
a radiopaque or bioactive agent that elutes from the coating or
otherwise interacts with the implant's environment in a desired
way.
[0183] Many substances that can enhance clinical performance can be
included in coatings of the stents of the present disclosure. For
instance, a radiopaque material, such as a dye or marker can be
used to allow for better positioning during implantation. These
markers can be placed on the ends of the stents as well as to mark
the location of an open or closed portion of the stent. Drugs and
bioactive agents that can enhance the clinical performance of the
stents of the present disclosure also can be included. Examples of
such drugs and bioactive agents include, for example and without
limitation, antineoplastic, antinflammatory, antiplatelet,
anticoagulant, antifibrin, antithromobin, antimitotic, antibiotic,
antiproliferative and antioxidant substances, as well as calcium
channel blockers, colchicine fibroblast growth factor antagonists,
histamine antagonists, 3-hydroxy-3-methylglutaryl coenzyme A
(HMG-CoA) reductase inhibitors, monoclonal antibodies,
phosphodiesterase inhibitors, prostaglandin inhibitors,
platelet-derived growth factor antagonists, serotonin inhibitors,
steroids, and thioprotease inhibitors. Additional substances can
include, for example and without limitation, rapamycin, cladribine,
heparin, nitrous oxide, nitric oxide, actinomycin D, as well as,
alpha-interferon, genetically engineered epithelial cells, and fish
oil (omega 3-fatty acid), des-aspartate angiotensin I, angiotensin
converting enzyme (ACE) inhibitors, angiotensin receptor blockers
(ARBs), statins (including without limitation cerivastatin),
hormones, and estradiol. Various combinations of such bioactive
agents and compounds, and analogs or derivatives of them, are
further contemplated and not to be considered a departure from the
intended scope of this disclosure.
[0184] In addition to other references herein incorporated by
reference, the following issued U.S. Patents are also herein
incorporated in their entirety by reference thereto: U.S. Pat. Nos.
6,293,967; 6,527,799; 6,540,774; 6,652,579; 6,796,997; and
7,018,400. The following published U.S. Patent Applications are
also herein incorporated in their entirety by reference thereto: US
2005/0119723; 2006/0050011; 2006/0100695; and 2006/0115512. The
following PCT Patent Application Publications are also herein
incorporated in their entirety by reference thereto: WO
2004/028571; WO 2005/053766; WO 2007/024484.
[0185] It is to be understood that the present invention is not
limited to the particular embodiments, materials, and examples
described herein, as these can vary, though such particularities
provided in the disclosure are considered nonetheless of particular
further value and benefit to the broader aspects and modes also
contemplated. It also is to be understood that the terminology used
herein is used for the purpose of describing particular embodiments
only, and is not intended to limit the scope of the present
invention. It must be noted that as used herein and in the appended
claims, the singular forms "a," "an," and "the" include the plural
reference unless the context clearly dictates otherwise. Thus, for
example, a reference to "a stent" is a reference to one or more
stents and includes equivalents thereof known to those skilled in
the art and so forth.
[0186] Unless defined otherwise, all technical terms used herein
have the same meanings as commonly understood by one of ordinary
skill in the art to which this invention belongs. Specific methods,
devices, and materials are described, although any methods and
materials similar or equivalent to those described herein can be
used in the practice or testing of the present invention.
[0187] Unless otherwise indicated, all numbers expressing
quantities of ingredients, properties such as molecular weight,
reaction conditions, and so forth used in the specification and
claims are to be understood as being modified in all instances by
the term "about." Accordingly, unless indicated to the contrary,
the numerical parameters set forth in the following specification
and attached claims are approximations that may vary depending upon
the desired properties sought to be obtained by the present
invention. At the very least, and not as an attempt to limit the
application of the doctrine of equivalents to the scope of the
claims, each numerical parameter should at least be construed in
light of the number of reported significant digits and by applying
ordinary rounding techniques. Notwithstanding that the numerical
ranges and parameters setting forth the broad scope of the
invention are approximations, the numerical values set forth in the
specific examples are reported as precisely as possible. Any
numerical value, however, inherently contains certain errors
necessarily resulting from the standard deviation found in their
respective testing measurements.
[0188] Recitation of ranges of values herein is merely intended to
serve as a shorthand method of referring individually to each
separate value falling within the range. Unless otherwise indicated
herein, each individual value is incorporated into the
specification as if it were individually recited herein. All
methods described herein can be performed in any suitable order
unless otherwise indicated herein or otherwise clearly contradicted
by context. The use of any and all examples, or exemplary language
(e.g. "such as") provided herein is intended merely to better
illuminate the invention and does not pose a limitation on the
scope of the invention otherwise claimed. No language in the
specification should be construed as indicating any non-claimed
element essential to the practice of the invention.
[0189] Groupings of alternative elements or embodiments of the
invention disclosed herein are not to be construed as limitations.
Each group member may be referred to and claimed individually or in
any combination with other members of the group or other elements
found herein. It is anticipated that one or more members of a group
may be included in, or deleted from, a group for reasons of
convenience and/or patentability. When any such inclusion or
deletion occurs, the specification is herein deemed to contain the
group as modified thus fulfilling the written description of all
Markush groups used in the appended claims.
[0190] Preferred embodiments of this invention are described
herein, including the best mode known to the inventors for carrying
out the invention. Of course, variations on those preferred
embodiments will become apparent to those of ordinary skill in the
art upon reading the foregoing description. The inventor expects
skilled artisans to employ such variations as appropriate, and the
inventors intend for the invention to be practiced otherwise than
specifically described herein. Accordingly, this invention includes
all modifications and equivalents of the subject matter recited in
the claims appended hereto as permitted by applicable law.
Moreover, any combination of the above-described elements in all
possible variations thereof is encompassed by the invention unless
otherwise indicated herein or otherwise clearly contradicted by
context.
[0191] Furthermore, numerous references are herein made to patents
and printed publications throughout this specification. Each of the
above cited references and printed publications are herein
individually incorporated by reference in their entirety.
[0192] It is to be understood that the particular embodiments
disclosed herein are illustrative of various broad aspects and
modes of the present invention. Each aspect, mode, embodiment, and
feature is considered of independent value and benefit without
requiring limitation by their combinations or further refinements
described, though such combinations and refinements are considered
of still further benefit and value. Other modifications that may be
employed by one of ordinary skill are considered within the scope
of the invention though such may not specifically described
hereunder. Thus, by way of example, but not of limitation,
alternative configurations of the present invention may be utilized
in accordance with the teachings herein. Accordingly, the present
invention is not limited to that precisely as shown and
described.
EXAMPLE 1
I. INTRODUCTION
[0193] Certain aspects of exemplary stent constructions consistent
with the present embodiments were modeled using 3-Dimensional
Finite Element Analysis (3-D FEA). These 3-D FEA models were
subjected to certain simulated deflection forces in order to
calculate, represent, and evaluate material strain distributions
variously within and between representative stent segments of the
models under conditions related to radial expansion and lateral
bending, respectively.
[0194] Similar 3-D FEA modeling and simulation was performed for
two additional stent designs intended to represent certain
commercially available stents. More specifically, these two
additional stent models were intended to represent certain aspects
of two cobalt-chromium stents of different designs, and from two
different manufacturers, and that represent the top selling bare
metal stents in the world: the "DRIVER.RTM." stent commercially
sold by Medtronic, and the "VISION.RTM." stent commercially sold
formerly by Guidant (currently sold by Abbott Vascular).
[0195] The 3-D FEA strain distributions during simulated radial
expansion and lateral bending, respectively, were displayed with
varied shading along the 3-D models, with results compared between
the various stents modeled.
II. MATERIALS AND METHODS
[0196] The LS-DYNA finite element program (Version 971) was used to
analyze stress-strain simulations of computer generated samples for
exemplary stent segments during (a) balloon expansion and (b) local
bending at the crossovers.
[0197] 3-D FEA models were created that were intended to represent:
(i) a "Model #1" for a stent constructed to incorporate similar
strut, crown, and cross-over features as that described above by
reference to FIGS. 1A-D, according, however to an 8-crown per
segment design; (ii) a "Model #2" intended to represent a stent
constructed with strut-crown segment features constructed according
to various aspects in common with those as described for the
exemplary embodiment above for FIGS. 2A-D, according, however to a
10-crown per segment design (iii) a "Model #3" intended to
represent a stent constructed to incorporate strut-crown segment
features similar to the embodiment of FIGS. 1A-D, but incorporating
crossover features similar to that of each of the embodiments of
FIGS. 1A-D and FIGS. 2A-D (for comparison purposes in lateral
bending simulation), and as also presented in an 8-crown per
segment design; (iv) a "Model #4" intended to illustrate certain
aspects similar to a Driver.RTM. stent, and (v) a "Model #5"
intended to illustrate certain aspects similar to a Vision.RTM.
stent.
[0198] Drawings for Models #1 and #2 were based upon 2-D CAD
drawings used to manufacture the stents, such as provided in FIGS.
1A and 2A, respectively, for the features simulated, and per
exemplary dimensions provided for various aspects noted above
(adjusted for generally expected outcomes post-processing to
finished goods, such as electropolishing). Similar 2-D CAD drawings
were used to create Model #3. 2-D CAD drawings for (iii)
Driver.RTM. and (iv) Vision.RTM. were created, and the 3-D modeling
completed, based upon inputs that reflected dimensional
measurements taken from commercially available products,
respectively.
[0199] Material properties of a cobalt-chrome alloy (L605) were
used for all models in order to isolate variables to highlight
affects of design differences on the performance features
evaluated. An elastic modulus of 243 GPa, yield stress of 547 MPa,
and a plastic modulus of 24 GPa were used as material parameters
for the analyses. It is understood that the Vision.RTM.
incorporates such similar L605 alloy in the commercial stent sold,
whereas the Driver.RTM. incorporates a different cobalt-chrome
alloy called "MP35N." However, in order to understand comparative
impact between design features of the various models in the study,
L605 properties were applied to all modeled stents in the study. It
is noted however to make clear, the estimated dimensions and
specific material properties assigned to the modeled stents based
upon these commercial stents likely do not match those actual
stents with perfect accuracy. Thus, this study, and results and
conclusions made, relate only to "estimated models" considered to
have certain "similarities" with these commercial stents, but do
not directly represent those actual commercial stents or their
manufacturers, nor capture or represent their actual
characteristics or performance.
[0200] Radial expansion of the stent was simulated as follows.
Initial stent crimping from the "cut" sizes to reduced "delivery"
sizes was simulated using non-compliant cylindrical mandrels. The
modeled stents in the simulated crimped conditions were then
subjected to the simulated radial expansion and lateral bending.
The radial expansion simulation was conducted to a maximum diameter
under assumed parameters representing a balloon inflated to 16 atm.
These simulated steps were performed to ensure the proper work
hardening and strain history for an elastic-plastic response. This
simulated radial expansion was performed for each of Models #1-2
and #4-5.
[0201] Local bending was simulated by placing a radial displacement
at the crossover connection and allowing the region between and
including adjacent crowns of the stent to react to the compressive
load. While not specifically a direct simulation of lateral bending
of a completed tubular stent constructed according to the models,
this set-up is believed to provide an indication of strain
distribution within and between the modeled stent segments during
bending, such as for example whether (and to what extent) the
crossover would allow a focal bend using the radial force produced
by the stent. The lateral bending simulation was performed for all
Models #1-5.
[0202] Results were displayed in 3-D FEA renderings of the various
stent features analyzed. Colorimetry and shading was performed to
display strain distribution, according to a color palette that
varies from low to high strain. Black and white or grey-scale
representations of the strain distribution were also captured for
the 3-D FEA models, and variously formed the bases for the
respective visual renderings provided in the respective Figures
referenced hereunder. More specifically, in these FIGS. 9-17,
lighter shading generally represents lower strain, with darker
shading representing higher strains.
III. RESULTS
[0203] A. Radial Expansion Simulation
[0204] 1. Model #1
[0205] FIG. 9 shows a 3-D FEA simulation and reflecting strain
distribution during simulated radial expansion for a peak-peak full
period section of Model #1. More specifically, FIG. 9 shows a stent
170 having a peak-peak amplitude 172 and constructed as to its
section features (e.g. strut, crown, and transition therebetween)
similar to that embodiment described above by reference to FIGS.
1A-D, provided here in an 8-crown per segment design. Strain
distribution is shown with respect to struts 180, crown 190
(including its outer and inner radii 192,194), and as revealed
through the cross-sectioned reduced thickness region 176 located at
the crown peak in this particular embodiment. Dark shading
representing higher levels of material strain is isolated to only
outer and inner radii 192,194 of the crowns 190. The significant
extent of the struts 180 are shown to reflect very low relative
strain. Accordingly, it is evident that material strain of Model #1
during radial expansion is principally concentrated (and thus most
of its expansion deformation occurs) along the sweeping outer and
inner radii 192,194 of its crowns 190.
[0206] 2. Model #2
[0207] FIG. 10 shows a 3-D FEA simulation and reflecting strain
distribution during simulated radial expansion for a peak-peak full
period section of Model #2. More specifically, FIG. 10 shows a
stent 200 modeled as to its sectional features (e.g. strut, crown,
and transition region therebetween) similar to that embodiment
described above by reference to FIGS. 2A-D, provided here in an
10-crown per segment design. Strain distribution under simulated
radial expansion environment is shown with respect to the struts
210, crowns 230 (including the outer and inner crown radii
232,234), transition shoulder region 220 between strut 210 and
crown 230, and as revealed through the cross-sectioned reduced
thickness region 236 located at the crown peak in this particular
embodiment. The strain experienced under expansion, while more
concentrated than the stress distribution for the sample, appears
to be distributed in a unique manner. Of particular note, the crown
230 appears to be devoid of, or at least experience very little,
strain at its peak (e.g. at its midline, such as centrally between
struts 210 and 212), including centrally in the strut and at the
outer radius 232 and inner radius 234 in this area. In fact, this
central crown region appears to experience the least strain of all
regions represented along the full period of
crown-strut-crown-strut-crown represented. This exceptionally low
stress, light shading is further reflected through the partial
cross-section taken through the crown peak midline at 236. Rather
than strain distribution across the crown and concentrated most at
this peak, as observed with other designs (such as Model #1), the
expansion strain appears to be distributed in a bifurcated manner
to the opposite transition shoulder regions 220 at either of sides
222,226 where crown 230 transitions into each of the two adjacent
struts 210,212 extending therefrom.
[0208] Accordingly, it is clear that the crown peak regions, as the
maximum width regions among the crown and strut (and transition
region) features of this design, are demonstrably the lowest
expansion strain region of the stent (including lower than the
mid-strut regions). Highest strain is reflected at tapering
transition regions 220 between strut 210 and crown 230, with the
strain concentration bifurcated to either side of each crown.
[0209] 3. Model #4
[0210] FIG. 11 shows a 3-D FEA simulation and reflecting strain
distribution during simulated radial expansion for a peak-peak full
period section of Model #4. More specifically, the simulated stent
240 includes a generally uniform filament thickness along the
entire strut-crown section, and simply features abrupt bends as
"elbows" in an otherwise generally uniform filament of fairly
constant thickness. This simple bent elbow crown feature bent into
an otherwise generally constant thickness filamental structure of
this model contrasts against other stents with designed "crowns"
with otherwise unique geometric features, such as provided in
various forms throughout the present embodiments. For example, in
comparison, the crown region of Model #1, while a more simple
arcuate design than for Model #2, nonetheless features a reduced
filament thickness versus the corresponding struts in a manner
different than this Model #4.
[0211] As seen in FIG. 11, the strain distribution under simulated
radial expansion for Model #4 appears generally isolated to the
outer and inner radii 262,264 its elbows 260. The entire length of
the strut 250 bridging between opposite facing elbows 260 reveals
very little strain along these features.
[0212] 4. Model #5
[0213] FIG. 12 shows a 3-D FEA simulation and reflecting strain
distribution during simulated radial expansion for a peak-peak full
period section of Model #5. More specifically, the modeled and
simulated stent 270 includes undulating filament pattern with
varied types of crowns and a crown-valley arrangement connecting
adjacent segments (ie. a connector bridges between a crown peak of
one segment facing one direction and a valley of a crown of an
adjacent segment facing the same direction). More specifically, the
stent 270 includes a connector 310 with a straight portion 312 and
a "U"-shaped portion 316. Straight portion 312 connects to crown
290 fairly centrally of the crown 290, whereas the "U"-shaped
portion 316 of the connector 310 is located between segments and
oriented transverse to the long axis of portion 312 and central
axis of crown 290. Crown 290 includes a subtle notch or valley 291,
rather than a peak, at its midline where connector 310 is
connected. Notch 291 sits between two partial peaks or bulbs
293,297 on either side of the connector 310. These two adjacent
bulbs 293,297 include right and left outer and inner radii 292,294
and 296,298, respectively. Struts 286,288 connect either side of
crown 290 to adjacent, opposite facing crowns 300 and 306. The
amplitude between crown 290 and crown 300 is shorter than that
between crown 290 and crown 300, in order to provide additional
space with the adjacent segment in which laterally oriented
"U"-shaped member 316 of connector 310 may reside.
[0214] According to these basic features for the Model #4 just
described, FIG. 12 shows the strain distribution is virtually
entirely focused within the respective outer and inner radii of
each of crowns 290, 300, and 306. This is shown for example at
outer and inner radii 302,304 for crown 300, as well as at outer
and inner radii for the other crowns (e.g. at 296,298 and 292,294).
Outside of these focal regions, the simulation reveals little to no
material strain or deformation in other regions during expansion,
such as for example struts 288 or connector 310.
[0215] B. Lateral Bending Simulation
[0216] 1. Model #1
[0217] FIG. 13 shows a 3-D FEA simulation and reflecting strain
distribution during simulated lateral bending deflection for a two
adjacent segment portion of stent 170 of Model #1 as follows. As is
apparent under the simulated force of deflection, strain appears to
be significantly localized to crossovers 184, and in particular at
their outer and inner surfaces 184,188 (with respect to the central
axis within the simulated tube around which the stent surrounds).
Very little strain or material deformation appears to be
experienced at other regions other than the cross-overs under the
environment of this simulation, including for example along struts
180 or at crowns 190, including at their outer and inner radii
192,194.
[0218] 2. Model #2
[0219] FIG. 14 shows a 3-D FEA simulation and reflecting strain
distribution during simulated lateral bending deflection for a two
adjacent segment portion of stent 200 of Model #2 as follows.
Cross-overs 238 between segments appear to experience very little
strain, and certainly do not appear to be a site of local strain
concentration, despite force of bending being applied at their
location. Rather, strain appears to be located principally at the
transition regions 220 between the respective crowns 230 and struts
210,212 in the design. Whereas a disparity in strain concentration
appears in FIG. 14 between each adjacent transition region 220 on
either side of the crown 230 associated with a cross-over being
deflected, this (and other artifacts such as other bending
responses to the simulated applied deflection forces) is believed
to represent an artifact of certain boundary parameters and
respective constraints of the simulated environment. It is believed
that the region of strain concentration at the transition regions
220 would be fairly uniformly distributed to either side of a given
crown in a full stent of similar construction as the portion shown
for Model #2, and under applied forces such as intended to be
simulated here.
[0220] 3. Model #3
[0221] FIG. 15 shows a 3-D FEA simulation and reflecting strain
distribution during simulated lateral bending deflection for a two
adjacent segment portion of Model #3 as follows.
[0222] The stent 170 shown for Model #3 in FIG. 15 is constructed
with "segment" features (e.g. struts 180, crowns 190, crown outer
and inner radii 192,194) similar to Model #1. Stent 170 of Model #3
also includes crossover 186 similar to Model #1. However, Model #3
differs from Model #1 by also providing another cross-over more
similar to those provided in Model #2. A further embodiment of the
present disclosure is thus presented, which combines the segment
features similar to Model #1 with a cross-over feature similar to
Model #2, and is explored as to certain characteristics during
simulated lateral bending. In doing so, for a stent of one similar
design as to its "segment" features (e.g. Model #3 is similar to
Model #1), the affects of different cross-overs between segments
may be evaluated during lateral bending simulation. In addition,
this "hybrid" aspect of Model #3 also provides an ability to
compare lateral bending strain distributions between stents sharing
a similar cross-over feature between adjacent segments, but with
different segment features, e.g. the different strut, crown, and
strut-crown transition segment features of Model #3 (similar to
Model #1) and Model #2.
[0223] As shown in FIG. 15, strain distribution at cross-over 186
appears to be very similar to that for Model #1 during lateral
bending. This result is sensible as virtually all local features,
crowns, struts, transitions, and cross-over, are similar between
the models in this region of Model #3. However, the strain
associated with lateral deflection forces at the region around the
other cross-over 238 appears to be uniquely distributed versus the
other Model #1 above. Here, strain appears to be distributed across
a region that principally includes most strain spread across the
adjacent lateral shoulders 193,195 on either side of the peaks for
the opposite facing crowns 190 on either longitudinal side of
cross-over 238. However, a slight strain appears to bridge between
the opposite facing crowns across the inner surface of cross-over
238. This relatively widely spread strain distribution in this
region, with highest levels at the two pairs of opposite crown
shoulders involved, is believed to result from the geometry of in
the design with the shoulders representing the smallest width
region of the overall design, and largest width region being the
cross-over. While this cross-over is larger in width, and of equal
thickness, than the struts, the slight strain distribution seen
there on its inner surface is believed to be mostly isolated to a
propagated result, featured mostly at the unbound surface,
responding to the focal strain in the four adjacent regions.
[0224] 4. Model #4
[0225] FIG. 16 shows a 3-D FEA simulation and reflecting strain
distribution during simulated lateral bending deflection for a two
adjacent segment portion of Model #4 as follows.
[0226] According to the representation of Model #4 shown, stent 240
includes two adjacent opposite facing elbows 260,266 that are
welded together, and their weld joint therebetween forms the
connection or linkage 268. Strain appears to be concentrated
principally at the shoulder regions 261,263 of these connected
elbows 260,266 on either side of their weld connection 268. The
struts 250,256 bordering either side of a welded elbow appear to
have relatively low strain other than at the shoulders 261,263.
Moreover, the linkage 268 and central peak regions of the elbows
260,268 appear to experience relatively low strain. Different than
the cross-over features associated with Model #2, however, this
distribution of the current model is associated with a direct
peak-peak weld joint, vs. an actual bridging cross-over features
that extends between peaks of the Model #2 design.
[0227] 5. Model #5
[0228] FIG. 17 shows a 3-D FEA simulation and reflecting strain
distribution during simulated lateral bending deflection for a two
adjacent segment portion of Model #1 as follows. Strain
distribution across stent 270 appears to be concentrated mostly in
two locations related to the connector 310 interconnecting and
extending between the adjacent segments 271,273. Namely, these
locations are at the U-shaped portion 316 transversely oriented
along the connector 310 between segments 271,273, and the end
section of the straight portion 312 of the connector 310 that
interfaces with and terminates into the valley of crown 290
opposite notch 291 between adjacent bulbs 293,297. While some
slight strain distribution is evidently extending slightly beyond
these locations, they are observed to represent fairly focal and
isolated strain locations in the simulated bending, with only
slight strain artifact propagating therefrom through the
surrounding material.
IV. ANALYSIS
[0229] A. Expansion Simulation
[0230] The expansion simulations performed yielded various
observations that distinguish the various models simulated.
[0231] Model #1 was observed to exhibit similar strain distribution
as that exhibited to Model #4, which each feature localized
concentration of strain at inner and outer radii of crown peaks.
However, Model #1 exhibits this with a reduced width filament at
this region versus adjacent struts extending from the respective
crown(s). This allows similar expansion characteristic as if the
filament was uniform across these features (as for Model #4), but
with additional benefits provided by wider struts at the lower
strain regions including without limitation enhanced visibility of
the wider strut region and increased surface area here for drug
delivery for example. Conversely, if the width of the struts of
that model #1 were uniform at the crown peaks with same increased
width vs. radial thickness as along the struts, the expansion
characteristics would likely be altered, such as for example:
requiring higher inflation pressure to produce similar strain at
the crowns necessary for expansion; potential for higher recoil;
and possibly adverse consequences of twisting of the crowns out of
plane when straining a planar structure of higher width than
thickness in the circumferential plane.
[0232] Model #2 was observed to uniquely distribute strain at the
crown shoulders in transition areas to the adjacent struts. This
was not observed in other crown designs of the other models. While
Model #5 provided certain bifurcated expansion characteristics at
some crown areas, these were only at locations of crown-valley
connectors, where the crown region itself was bifurcated into two
adjacent bulbs on either side of the connector. Outside of these
specific limited crowns in that model, the other primary crowns
demonstrated similar strain distributions at inner/outer radii of
the crown peaks. The Model #2 expansion characteristic is thus
unique as compared against all other models simulated or otherwise
known.
[0233] B Lateral Bending Simulation
[0234] Bending simulation yielded different observations regarding
strain distribution between the models simulated, as follows.
[0235] Model #1 was observed to exhibit localized bending strain at
the cross-overs between segments having reduced width. Model #2 was
observed to distribute strain principally at transition regions of
struts into two opposite shoulders of the crowns, with no or lowest
strain at the crossover regions of increased width versus other
adjacent filamental features of the overall structure. This
difference in bending strain distribution between crossover designs
was observed in Model #3 which included each of these two different
crossover features in one stent otherwise carrying segmental
features of Model #1. It is believed that the bifurcated bending
strain distribution between adjacent shoulder transitions with
struts provides a particularly robust approach with certain
particular benefits, including for example enhanced fatigue
integrity and recoil following radial expansion (or
compression).
[0236] Model #4 was observed to also bifurcate bending strain to
adjacent strut transitions to the crossover feature in that design,
but results from direct weld joints that are required between
directly confronting crowns of adjacent segments, and in a design
with uniform width across the overall filamental structure. The
different approach of integral crossovers of increased width
extending between facing crown peaks, e.g. Model #2, is considered
to provide distinct benefits in achieving this resulting strain
distribution, including without limitation removing the need for
(and various issues associated with) weld joints. Other prior
stents that incorporate either connectors or cross-over extensions
between adjacent segments generally intend this feature to provide
lateral bending flexibility for the stent. However, Model #2
represents a significant departure from this convention, with its
respective cross-over region representing a region of locally
increased width along the stent filament, and very little if any
bending strain localized here (which is transferred in this model
to the transition regions adjacent the shoulders).
[0237] Model #5 was observed to distribute bending strain along
extended flexible connectors, which are provided in that model
generally for that purpose.
V. CONCLUSIONS
[0238] According to the observations made in the expansion and
bending simulations performed across the various models, particular
benefits are believed to be presented by the unique combinations of
features and incumbent performance associated with the designs
presented by Model #1, and in particular Model #2.
EXAMPLE 2
[0239] Twenty pigs underwent coronary artery placement of 22 stents
of two types as follows: commercially available Driver.RTM. stents
(n=10); and a physical embodiment similar to that described above
with respect to FIGS. 2A-D, referred to here as "Model #2" (n=12)
as incorporating similar features as presented for Model #2 in
Example #1 simulations presented above. Stents used from each group
were provided for intended use in 3.0 mm or 3.5 mm diameter sizes,
and were all 18 mm in length. Average vessel diameter at implant
was 2.89 mm for the Model #1 group, and 3.04 mm for the Driver.RTM.
group.
[0240] At day 28, animals were re-studied for angiographic
endpoints variously represented in Tables 2A-4B. Certain criteria
were measured or calculated and included in these Tables as
follows. "Balloon-to-Artery" ratio is a measure of balloon
oversizing as related to reference vessel diameter at the time of
implant. "Acute gain" is the increase in vessel diameter due to
stenting, measured immediately post-stent. "Percent stenosis" was
calculated via the recognized equation: [1-(in-stent Minimum Lumen
Diameter/reference diameter)].times.100. "Late Loss" is a
calculation of post-stent minimum lumen diameter (measured
immediately following implant) minus follow-up minimum lumen
diameter (measured at 28 days, here via QCA).
[0241] Tables 2A and 2B represent the chronic 28 day restenosis
results via QCA for the Driver.RTM. group on the whole, and after
removing highest and lowest data points, respectively. Tables 3A
and 3B represent the chronic 28 day restenosis results via QCA for
the Model #2 group on the whole, and after removing highest and
lowest data points, also respectively.
[0242] The balloon to artery ratios of both groups were similar
(1.16.+-.0.06 for the Driver.RTM. and 1.14.+-.0.04 for Model #1)
which suggests that differences in percent stenosis were not
related to differences in injury to the vessels. Negative numbers
for follow-up percent stenosis are related to the vessel remaining
oversized from initial stent implantation, and not due to aneurysms
outside of the stent (e.g. a 14% overstretch may result in some
neointimal formation to fill in the overstretch region, with
reduction in cross-sectional diameter or area post implantation,
yet still produce a negative percent stenosis number so long as the
cross-section there remains larger than the reference vessel.
[0243] Table 4A represents the summary Driver.RTM. data of Table 2A
against the summary Model #2 average data of Table 3A. At day 28,
the average percent restenosis results for the Medtronic
Driver.RTM. group (12%.+-.26%) was 760% greater than that of the
Model #2 group (2%.+-.11%). This comparison is further demonstrated
in graphical form in FIG. 18. Also compared is the late loss
between the test groups. Table 4B shows comparison of average
percent stenosis and late loss between the test groups according to
the adjusted data of Tables 2B and 3B, respectively. In addition to
resulting in substantially lower average percent stenosis than the
comparison bare metal stent in this experiment, it is further noted
that the average percent stenosis at 28 days for Model #2 results
appear similar, or at least close, to percent stenosis results
observed at 28 days in similar pre-clinical animal testing
conducted for at least one leading drug eluting stent product.
[0244] Although the description above contains many details, these
should not be construed as limiting the scope of the invention but
as merely providing illustrations of some of the presently
preferred embodiments of this invention. Therefore, it will be
appreciated that the scope of the present invention fully
encompasses other embodiments which may become obvious to those
skilled in the art, and that the scope of the present invention, to
the extent presented by claims appended hereto, is accordingly to
be limited by nothing other than such appended claims, in which
reference to an element in the singular is not intended to mean
"one and only one" unless explicitly so stated, but rather "one or
more." All structural, chemical, and functional equivalents to the
elements of the above-described preferred embodiment that are known
to those of ordinary skill in the art are expressly incorporated
herein by reference and are intended to be encompassed by the
present claims. Moreover, it is not necessary for a device or
method to address each and every problem sought to be solved by the
present invention, for it to be encompassed by the present claims.
Furthermore, no element, component, or method step in the present
disclosure is intended to be dedicated to the public regardless of
whether the element, component, or method step is explicitly
recited in the claims. No claim element herein is to be construed
under the provisions of 35 U.S.C. .sctn.112, sixth paragraph,
unless the element is expressly recited using the phrase "means
for."
TABLE-US-00001 TABLE 1 Number of Crossovers and Crossover Positions
of Certain Present Embodiments FIG. 1A FIG. 2A FIG. 3A FIG. 4 FIG.
5 FIG. 6A FIG. 7A # of # of # of # of # of # of # of Crossovers
Crossovers Crossovers Crossovers Crossovers Crossovers Crossovers
Crossover 10 Crowns 10 Crowns 9 Crowns 8 Crown 7 Crown 6 Crown 6
Crown Position 18 Sections 18 Sections 15 Sections 18 Sections 15
Sections 15 Sections 15 Sections 1 4 4 3 3 2 3 2 (2, 8, 12, 18) (2,
8, 12, 18) (2, 8, 14) (2, 8, 14) (4, 10) (2, 6, 10) (2, 8) 2 2 2 2
2 2 2 2 (5, 15) (5, 15) (5, 13) (5, 13) (7, 13) (5, 11) (5, 11) 3 2
2 2 2 2 2 2 (10, 20) (10, 20) (10, 18) (8, 16) (2, 10) (2, 8) (2,
8) 4 2 2 2 2 2 2 2 (5, 15) (5, 15) (5, 15) (3, 11) (5, 13) (5, 11)
(5, 11) 5 2 2 2 2 2 2 2 (10, 20) (10, 20) (2, 10) (6, 14) (2, 8)
(2, 8) (2, 8) 6 2 2 2 2 2 2 2 (5, 15) (5, 15) (7, 15) (1, 9) (5,
11) (5, 11) (5, 11) 7 2 2 2 2 2 2 2 (10, 20) (10, 20) (2, 12) (4,
12) (8, 14) (2, 8) (2, 8) 8 2 2 2 2 2 2 2 (5, 15) (5, 15) (7, 17)
(7, 15) (3, 11) (5, 11) (5, 11) 9 2 2 2 2 2 2 2 (10, 20) (10, 20)
(4, 12) (2, 10) (6, 14) (2, 8) (2, 8) 10 2 2 2 2 2 2 2 (5, 15) (5,
15) (9, 17) (8, 16) (3, 9) (5, 11) (5, 11) 11 2 2 2 2 2 2 2 (10,
20) (10, 20) (4, 14) (3, 11) (6, 12) (2, 8) (2, 8) 12 2 2 2 2 2 2 2
(5, 15) (5, 15) (1, 9) (6, 14) (1, 9) (5, 11) (5, 11) 13 2 2 2 2 2
2 2 (10, 20) (10, 20) (6, 14) (1, 9) (4, 12) (2, 8) (2, 8) 14 2 2 3
2 2 3 2 (5, 15) (5, 15) (5, 11, 17) (4, 12) (1, 7) (1, 5, 9) (5,
11) 15 2 2 2 (10, 20) (10, 20) (7, 15) 16 2 2 2 (5, 15) (5, 15) (4,
8) 17 4 4 3 (2, 8, 12, 18) (2, 8, 12, 18) (4, 10, 14)
TABLE-US-00002 TABLE 2A Angiographic results of Driver .RTM. Stents
Implanted under Example #2 Late Animal B/A Acute F/U % loss Number
Vessel Description Ratio gain (mm) stenosis (mm) 3810 LCX Driver
1.14 0.40 0.0% 0.10 3812 RCA Driver 1.22 0.60 1.9% 0.70 3813 LAD
Driver 1.23 0.70 -10.3% 0.50 3817 RCA Driver 1.07 0.20 9.7% 0.40
3821 LCX Driver 1.20 0.50 13.8% 1.00 3830 LAD Driver 1.21 0.50
65.5% 2.40 3831 LAD Driver 1.09 0.30 45.7% 1.90 3834 LCX Driver
1.19 0.60 -25.9% 0.30 3836 RCA Driver 1.09 0.30 7.1% 1.20 3837 LAD
Driver 1.15 0.40 9.1% 1.30 Mean 1.16 0.45 11.7% 0.98 SD 0.06 0.16
26.3% 0.74
TABLE-US-00003 TABLE 2B Driver .RTM. results of Table 2A following
removal of highest and lowest data points Acute Late Animal B/A
gain F/U % loss Number Vessel Description Ratio (mm) stenosis (mm)
3810 LCX Driver 1.14 0.40 0% 0.10 3812 RCA Driver 1.22 0.60 2% 0.70
3813 LAD Driver 1.23 0.70 -10% 0.50 3817 RCA Driver 1.07 0.20 10%
0.40 3821 LCX Driver 1.20 0.50 14% 1.00 3831 LAD Driver 1.09 0.30
46% 1.90 3836 RCA Driver 1.09 0.30 7% 1.20 3837 LAD Driver 1.15
0.40 9% 1.30 Mean 1.15 0.43 10% 0.89 SD 0.07 0.17 16% 0.58
TABLE-US-00004 TABLE 3A Angiographic results of "Model #2" Stents
Implanted under Example #2 Late Animal B/A Acute F/U % loss Number
Vessel Description Ratio gain (mm) stenosis (mm) 3807 RCA Model #2
1.11 0.30 0.0% 0.30 3812 LAD Model #2 1.13 0.40 -3.7% 0.60 3816 RCA
Model #2 1.13 0.10 7.4% 0.60 3819 LAD Model #2 1.15 0.40 0.0% -0.10
3820 LAD Model #2 1.21 0.50 -3.4% 0.40 3827 RCA Model #2 1.16 0.50
-2.9% 0.00 3832 RCA Model #2 1.15 0.40 10.6% 1.00 3835 RCA Model #2
1.09 0.30 1.8% 0.90 3838 LCX Model #2 1.14 0.40 -6.7% 0.10 3840 LCX
Model #2 1.16 0.40 -10.0% 0.20 3825 LCX Model #2 1.15 0.40 30.9%
1.10 3813 LCX Model #2 1.07 0.20 -5.7% 0.20 Mean 1.14 0.36 1.5%
0.44 SD 0.04 0.12 10.9% 0.40
TABLE-US-00005 TABLE 3B Model #2 results of Table 3A after removing
highest and lowest data points Acute Late Animal B/A gain F/U %
loss Number Vessel Description Ratio (mm) stenosis (mm) 3807 RCA
Model #2 1.11 0.30 0.0% 0.30 3812 LAD Model #2 1.13 0.40 -3.7% 0.60
3816 RCA Model #2 1.13 0.10 7.4% 0.60 3819 LAD Model #2 1.15 0.40
0.0% -0.10 3820 LAD Model #2 1.21 0.50 -3.4% 0.40 3827 RCA Model #2
1.16 0.50 -2.9% 0.00 3832 RCA Model #2 1.15 0.40 10.6% 1.00 3835
RCA Model #2 1.09 0.30 1.8% 0.90 3838 LCX Model #2 1.14 0.40 -6.7%
0.10 3813 LCX Model #2 1.07 0.20 -5.7% 0.20 Mean 1.13 0.35 -0.3%
0.40 SD 0.04 0.13 5.6% 0.37
TABLE-US-00006 TABLE 4A Comparison of Driver .RTM. results Table 2A
vs. Model #2 results Table 3A Model #2 Driver .RTM. % Difference
F/U % Stenosis 1.5% 11.7% 761% Late Loss (mm) 0.44 0.98 222%
TABLE-US-00007 TABLE 4B Comparison of Driver .RTM. results Table 2B
vs. Model #2 results Table 3B % Reduction Model #2 Driver .RTM.
(From Driver .RTM. to Model #2) F/U % Stenosis 0% 9.6% 100% Late
Loss (mm) 0.40 0.89 55%
* * * * *