U.S. patent application number 13/687977 was filed with the patent office on 2013-04-11 for highly flexible stent and method of manufacture.
This patent application is currently assigned to C. R. Bard, Inc.. The applicant listed for this patent is C. R. Bard, Inc.. Invention is credited to Thomas O. Bales, JR., Scott L. Jahrmarkt, Peter K. Kratsch, Charles R. Slater.
Application Number | 20130090719 13/687977 |
Document ID | / |
Family ID | 43413090 |
Filed Date | 2013-04-11 |
United States Patent
Application |
20130090719 |
Kind Code |
A1 |
Bales, JR.; Thomas O. ; et
al. |
April 11, 2013 |
Highly Flexible Stent and Method of Manufacture
Abstract
Preferred embodiments of a stent with a high degree of
flexibility are shown and described. The stent can include a
continuous helical winding having interconnected struts joined at
vertices, and having bridges connecting sections of the helical
winding to each other. An annular ring can be provided at one or
both ends of the helical winding, and the annular ring can have
five extensions extending to connect to the helical winding. One of
the extensions can connect to a bridge and another extension can
connect to a vertex. The struts at the ends of the helical winding
can have strut lengths that differ from the strut lengths of the
struts in a central portion of the winding between the ends of the
winding.
Inventors: |
Bales, JR.; Thomas O.;
(Coral Gables, FL) ; Jahrmarkt; Scott L.; (Miami
Beach, FL) ; Slater; Charles R.; (Fort Lauderdale,
FL) ; Kratsch; Peter K.; (Davie, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
C. R. Bard, Inc.; |
Murray Hill |
NJ |
US |
|
|
Assignee: |
C. R. Bard, Inc.
Murray Hill
NJ
|
Family ID: |
43413090 |
Appl. No.: |
13/687977 |
Filed: |
November 28, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12526711 |
Jun 11, 2010 |
8333799 |
|
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PCT/US2008/053319 |
Feb 7, 2008 |
|
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13687977 |
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60889428 |
Feb 12, 2007 |
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Current U.S.
Class: |
623/1.16 ;
156/169 |
Current CPC
Class: |
B32B 37/14 20130101;
A61F 2/89 20130101; A61F 2/91 20130101; A61F 2/88 20130101; A61F
2230/0054 20130101 |
Class at
Publication: |
623/1.16 ;
156/169 |
International
Class: |
A61F 2/89 20060101
A61F002/89; B32B 37/14 20060101 B32B037/14 |
Claims
1. A method of manufacturing an implantable prosthesis, comprising:
forming a first pattern defining a continuous helical winding
having a plurality of circumferential sections circumscribing a
longitudinal axis from a first end to a second end, the
circumferential sections being spaced apart along the axis and
including a plurality of struts joined together end-to-end, the
end-to-end joining of two struts of the plurality of struts
defining a vertex between the two struts, a plurality of bridges
connecting one circumferential section to an adjacent
circumferential section; and forming a second pattern defining an
annular ring having five extensions with a first extension and a
second extension extending from the annular ring connecting to the
first or second ends of the continuous helical winding, the first
extension connecting to an end vertex at the first or second end,
the second extension connecting to one of the plurality of bridges,
the annular ring including a plurality of struts with adjacent
struts joined together.
2. The method according to claim 1, wherein the forming a first
pattern comprises forming the plurality of bridges to have a
minimum width greater than a width of any of the plurality of
struts.
3. The method according to claim 1, wherein the forming a first
pattern comprises defining the continuous helical winding as a
single helical winding.
4. The method according to claim 1, wherein the forming a first
pattern comprises defining the continuous helical winding as
separate helical windings connected to each other.
5. The method according to claim 1, wherein the forming a first
pattern comprises forming the plurality of bridges to extend
substantially parallel with respect to the longitudinal axis.
6. The method according to claim 1, wherein the forming a first
pattern comprises forming the plurality of bridges such that at
least one of the bridges extends obliquely with respect to an axis
extending parallel to the longitudinal axis.
7. The method according to claim 1, wherein the forming a first
pattern comprises forming the plurality of bridges such that at
least one of the bridges directly connects a peak of one
circumferential section to another peak of an adjacent
circumferential section.
8. The method according to claim 1, wherein the forming a first
pattern comprises forming the plurality of bridges such that at
least one of the bridges directly connects a peak of one
circumferential section to a trough of an adjacent circumferential
section.
9. The method according to claim 1, wherein the forming a first
pattern comprises forming the plurality of bridges such that at
least one of the bridges directly connects a trough of one
circumferential section to a trough of an adjacent circumferential
section.
10. The method according to claim 1, wherein the forming a first
pattern comprises forming the plurality of struts to have a width
of approximately 65 microns.
11. An implantable prosthesis comprising: forming a first pattern
defining a continuous helical winding having a plurality of
circumferential sections circumscribing a longitudinal axis from a
first end to a second end, the circumferential sections including a
first end circumferential section at the first end and a second end
circumferential section at the second end and one or more central
circumferential sections therebetween, the circumferential sections
being spaced apart along the axis and including a plurality of
struts joined together end-to-end, the end-to-end joining of two
struts of the plurality of struts defining a vertex between the two
struts, at least one of the vertices of the first or second end
circumferential sections being an end vertex formed by a joining of
two final struts of the first or second end circumferential
sections, a plurality of bridges connecting one circumferential
section to an adjacent circumferential section; and forming a
second pattern defining an annular ring having five extensions
extending therefrom and connecting to the continuous helical
winding, at least one extension connecting to the end vertex, at
least one of the two final struts joining together to define the
end vertex having an end strut length, the end strut length being
different than a range of central strut lengths of the struts of
the one or more central circumferential sections.
12. The method according to claim 11, wherein the forming a first
pattern comprises forming the plurality of bridges to have a
minimum width greater than a width of any of the plurality of
struts.
13. The method according to claim 11, wherein the forming a first
pattern comprises defining the continuous helical winding as a
single helical winding.
14. The method according to claim 11, wherein the forming a first
pattern comprises defining the continuous helical winding as
separate helical windings connected to each other.
15. The method according to claim 11, wherein the forming a first
pattern comprises forming the plurality of bridges to extend
substantially parallel with respect to the longitudinal axis.
16. The method according to claim 11, wherein the forming a first
pattern comprises forming the plurality of bridges such that at
least one of the bridges extends obliquely with respect to an axis
extending parallel to the longitudinal axis.
17. The method according to claim 11, wherein the forming a first
pattern comprises forming the plurality of bridges such that at
least one of the bridges directly connects a peak of one
circumferential section to another peak of an adjacent
circumferential section.
18. The method according to claim 11, wherein the forming a first
pattern comprises forming the plurality of bridges such that at
least one of the bridges directly connects a peak of one
circumferential section to a trough of an adjacent circumferential
section.
19. The method according to claim 11, wherein the forming a first
pattern comprises forming the plurality of bridges such that at
least one of the bridges directly connects a trough of one
circumferential section to a trough of an adjacent circumferential
section.
20. The method according to claim 11, wherein the forming a first
pattern comprises forming the plurality of struts to have a width
of approximately 80% of a width of the plurality of bridges.
Description
PRIORITY DATA AND INCORPORATION BY REFERENCE
[0001] This application is a division of U.S. patent application
Ser. No. 12/526,711, filed as a U.S. national stage application
under 35 U.S.C. .sctn.371 of International Application No.
PCT/US2008/053319, filed on Feb. 7, 2008, which claims the benefit
of priority to U.S. Provisional Application No. 60/889,428, filed
on Feb. 12, 2007, each of which is incorporated by reference in its
entirety into this application. International Application No.
PCT/US2007/061917 filed on Feb. 9, 2007 is also incorporated by
reference in its entirety into this application.
BACKGROUND ART
[0002] It is known in the medical field to utilize an implantable
prosthesis to support a duct or vessel in a mammalian body. One
such prosthesis may include a frame-like structure. Such frame-like
structures are commonly known as a "stent", "stent-graft" or
"covered stent." These structures are referred to collectively
herein as a "stent" or an "implantable prosthesis."
[0003] The stent or prosthesis can be utilized to support a duct or
vessel in the mammalian body that suffers from an abnormal widening
(e.g., an aneurysm, vessel contraction or lesion such as a stenosis
or occlusion), or an abnormal narrowing (e.g., a stricture). Stents
are also utilized widely in the urethra, esophagus, biliary tract,
intestines, arteries, veins, as well as peripheral vessels. The
stent can be delivered via a small incision on a host body. Hence,
the use of stents as a minimally-invasive surgical procedure has
become widely accepted.
[0004] Previously developed stents for use in the biliary, venous,
and arterial systems have been of two broad classes:
balloon-expanded and self-expanding. In both of these classes,
stents have been made by different techniques, including forming
from wire and machining from a hollow tube. Such machining can be
done by photo-chemical etching, laser-cutting, stamping, piercing,
or other material-removal processes. Other manufacturing techniques
have been proposed, such as vacuum or chemical deposition of
material or forming a tube of machined flat material, but those
"exotic" methods have not been widely commercialized.
[0005] One common form of stent is configured as a series of
essentially identical rings connected together to form a
lattice-like framework that defines a tubular framework. The series
of rings may or may not have connecting linkages between the
adjacent rings. One example does not utilize any connecting
linkages between adjacent rings as it relies upon a direct
connection from one ring to the next ring. It is believed that more
popular examples utilize connecting linkages between adjacent
rings, which can be seen in stent products offered by various
companies in the marketplace.
[0006] All of the above stent examples utilize a biocompatible
metal alloy (e.g., stainless steel, Nitinol or Elgiloy). The most
common metal alloy utilized by these examples is Nitinol, which has
strong shape memory characteristics so that Nitinol self-expands
when placed in the duct or vessel of a mammalian body at normal
body temperature. In addition to self-expansion, these stents
utilize a series of circular rings placed adjacent to each other to
maintain an appropriate longitudinal spacing between each rings.
Other examples are shown and described in U.S. Patent Publications
2004/0267353 and 2003/055485, and U.S. Pat. No. 5,824,059. Examples
which use a helical configuration are shown and described, to
identify a few, in U.S. Pat. Nos. 6,117,165; 6,488,703; 6,042,597;
5,906,639; 6,053,940; 6,013,854; 6,348,065; 6,923,828; 6,059,808;
6,238,409; 6,656,219; 6,053,940; 6,013,854; and 5,800,456.
[0007] A need is recognized for a stent that maintains the patency
of a vessel with the ability to adapt to the tortuous anatomy of
the host by being highly flexible while being loadable into a
delivery catheter of sufficiently small profile and easily
deliverable to target site in the vessel or duct by having the
ability to navigate tortuous ducts or vessels.
DISCLOSURE OF INVENTION
[0008] The embodiments described herein relate to various
improvements of the structure of an implantable stent that embodies
a helical winding. More specifically, the preferred embodiments
relate to a stent with a continuous helical winding having
interconnected struts joined at vertices, and having bridges
connecting sections of the helical winding to each other. At least
one end of the stent has an annular ring connected to the helical
winding with five extensions extending therebetween. At least one
extension extends from the annular ring to connect to a bridge and
at least one extension extends from the annular ring to connect to
a vertex. The struts at the ends of the helical winding also have
strut lengths that differ from the strut lengths of the struts in a
central portion of the helical winding.
[0009] One aspect includes an implantable prosthesis with a
continuous helical winding. The winding has a plurality of
circumferential sections circumscribing a longitudinal axis from a
first end to a second end to define a tube. The circumferential
sections are spaced apart along the axis and include a plurality of
struts joined together end to end. The end to end joining of two
struts of the plurality of struts defines a vertex between the two
struts. A plurality of bridges connect one circumferential section
to an adjacent circumferential section. An annular ring with five
extensions with a first extension and a second extension that
extend from the annular ring and connect to the first or second
ends of the continuous helical winding. The first extension
connects to an end vertex at the first or second end, and the
second extension connects to one of the plurality of bridges.
[0010] Another aspect includes an implantable prosthesis with a
continuous helical winding. The winding has a plurality of
circumferential sections circumscribing a longitudinal axis from a
first end to a second end to define a tube. The circumferential
sections include a first end circumferential section at the first
end and a second end circumferential section at the second end and
one or more central circumferential sections therebetween. The
circumferential sections are spaced apart along the axis and
include a plurality of struts joined together end to end. The end
to end joining of two struts of the plurality of struts defines a
vertex between the two struts. At least one of the vertices of the
first or second end circumferential sections is an end vertex, and
a plurality of bridges connect one circumferential section to an
adjacent circumferential section. An annular ring has five
extensions that extend from the annular ring and connect to the
continuous helical winding. At least one extension connects to the
end vertex, and at least one of the two struts joined together to
define the end vertex has an end strut length. The end strut length
is different than a range of central strut lengths of the struts of
the one or more central circumferential sections.
[0011] These aspects can include the helical winding and the
plurality of bridges having an expanded and unimplanted condition.
The helical winding can include zig-zag struts, the plurality of
bridges can have a minimum width greater than a width of any strut,
and the helical winding can have a single helical winding. The
helical winding can also have a plurality of separate helical
windings connected to each other, at least one of the plurality of
bridges can extend substantially parallel with respect to the axis
of the implantable prosthesis, and at least one of the plurality of
bridges can extend obliquely with respect to an axis extending
parallel to the axis of the implantable prosthesis. Furthermore, at
least one of the plurality of bridges can directly connect a peak
of one circumferential section to another peak of an adjacent
circumferential section, at least one of the plurality of bridges
can directly connect a peak of one circumferential section to a
trough of an adjacent circumferential section, and at least one of
the plurality of bridges can directly connect a trough of one
circumferential section to a trough of an adjacent circumferential
section. Also, a width of at least one strut can be approximately
65 microns, and a width of at least one strut can be approximately
80% of a width of at least one of the plurality of bridges.
[0012] Yet another aspect includes a method of manufacturing an
implantable prosthesis involving forming a first pattern that
defines a continuous helical winding having a plurality of
circumferential sections with a first end and a second end. The
circumferential sections are spaced apart between the first and
second ends and include a plurality of struts joined together end
to end. The end to end joining of two struts of the plurality of
struts defines a vertex between the two struts, and a plurality of
bridges connect one circumferential section to an adjacent
circumferential section. The method also involves forming a second
pattern that defines an annular ring having five extensions with a
first extension and a second extension that extend from the annular
ring and connect to the first or second ends of the continuous
helical winding. The first extension connects to an end vertex at
the first or second end, and the second extension connects to one
of the plurality of bridges.
[0013] Still another aspect includes a method of manufacturing an
implantable prosthesis involving forming a first pattern that
defines a continuous helical winding having a plurality of
circumferential sections with a first end and a second end. The
circumferential sections include a first end circumferential
section at the first end and a second end circumferential section
at the second end and one or more central circumferential sections
there between. The circumferential sections are spaced apart and
include a plurality of struts joined together end to end. The end
to end joining of two struts of the plurality of struts defines a
vertex between the two struts, and at least one of the vertices of
the first or second end circumferential sections is an end vertex.
A plurality of bridges connect one circumferential section to an
adjacent circumferential section.
[0014] The method also includes forming a second pattern that
defines an annular ring having five extensions extending from the
annular ring and connecting to the continuous helical winding. At
least one extension connects to the end vertex, and at least one of
the two struts joined together to define the end vertex has an end
strut length. The end strut length is different than a range of
central strut lengths of the struts of the one or more central
circumferential sections.
[0015] These and other embodiments, features and advantages will
become apparent to those skilled in the art when taken with
reference to the following detailed description in conjunction with
the accompanying drawings that are first briefly described.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The accompanying drawings, which are incorporated herein and
constitute part of this specification, illustrate exemplary
embodiments of the invention, and, together with the general
description given above and the detailed description given below,
serve to explain the features of the invention.
[0017] FIG. 1 is a side view of a helical type stent of the
preferred embodiment.
[0018] FIG. 2 is a perspective view of a portion of the stent of
FIG. 1.
[0019] FIG. 3 is a close-up, perspective view of the stent of FIG.
2.
[0020] FIG. 3A is a close-up, perspective view of an alternate
embodiment of a bridge connection illustrated in FIG. 3.
[0021] FIG. 4 is a close-up side view of a bridge connection of the
stent of FIG. 1.
[0022] FIG. 5A is a close-up partial side view of an end portion of
the stent of FIG. 1.
[0023] FIG. 5B is a close-up partial side view of an end portion of
the stent of FIG. 1 in an unexpanded configuration.
[0024] FIG. 6 is a close-up partial side view illustrating the
loading forces and distortion of an alternative embodiment of the
bridge connection.
[0025] FIG. 7 is a close-up partial side view of an embodiment of
the stent in an unexpanded configuration.
[0026] FIG. 8 is a side view of a portion of an alternative stent
to the stent of FIG. 1.
[0027] FIG. 9 illustrates a testing stand to determine flexibility
of the preferred stent in a delivery catheter.
[0028] FIG. 10 is a side view of a portion of another alternative
stent to the stent of FIG. 1.
[0029] FIG.11 is a side view of an end of a helical type stent of
another preferred embodiment.
[0030] FIG. 12 is a perspective view of the end of the stent of
FIG.11.
[0031] FIG. 13 is an unrolled view of the end of the stent of FIG.
11, with the stent of FIG. 11 longitudinally separated along a cut
line and laid unrolled along a flat plane in an expanded
configuration.
MODE(S) FOR CARRYING OUT THE INVENTION
[0032] The following detailed description should be read with
reference to the drawings, in which like elements in different
drawings are identically numbered. The drawings, which are not
necessarily to scale, depict selected embodiments and are not
intended to limit the scope of the invention. The detailed
description illustrates by way of example, not by way of
limitation, the principles of the invention. This description will
clearly enable one skilled in the art to make and use the
invention, and describes several embodiments, adaptations,
variations, alternatives and uses of the invention, including what
is presently believed to be the best mode of carrying out the
invention.
[0033] As used herein, the terms "about" or "approximately" for any
numerical values or ranges indicate a suitable dimensional
tolerance that allows the part or collection of components to
function for its intended purpose as described herein. Also, as
used herein, the terms "patient", "host" and "subject" refer to any
human or animal subject and are not intended to limit the systems
or methods to human use, although use of the subject invention in a
human patient represents a preferred embodiment.
[0034] Referring to FIGS. 1 and 2, a stent 100 is shown having a
tubular shape and a first end 10, a second end 12, an intermediate
portion 14, and a longitudinal axis 16. The intermediate portion 14
includes a continuous helical winding 18. The winding 18 has a
plurality of circumferential sections 20 (identified as 20a-20g in
FIG. 1) that join together end-to-end and circumscribe the axis 16
from the first end 10 to the second end 12, with the continuation
of each circumferential section 20 along the path of the helical
winding 18 represented with dashed lines in FIG. 1. In FIGS.1, 2,
8, and 10-12, the portions of the stent 100 (or stents 200, 300, or
400) in the background of the figure are not shown in detail, for
clarity and to clearly show identical features already presented in
the foreground of the figure. The circumferential sections 20 are
longitudinally spaced apart along the axis 16 and disposed 360
degrees about the axis 16. The axial distances between adjacent
circumferential sections 20 define spacing 22, and the spacing 22
is shown in FIG. 1 with the same dashed lines that represent the
continuation of the helical winding 18 for each circumferential
section 20 in the background of the figure. The spacing 22 of each
circumferential section 20 defines a helical angle 24 relative to a
plane collinear with the axis 16 (as shown) or relative to an
orthogonal plane intersecting the axis 16, with each
circumferential section 20 having a helical angle on a first-end
facing side and a second-end facing side. Although only one helical
winding 18 is illustrated in FIG. 1, more that one helical winding
18 can be employed in the stent 100. For example, a helical winding
with a first helical angle can be connected or coupled with another
helical winding that has a different second helical angle.
Alternatively, the helical winding 18 of FIG. 1 can be utilized as
a central portion of the intermediate portion 14 and the helical
winding 218 of the stent 200 illustrated in FIG. 8 can be utilized
proximate each end of the intermediate portion 14, and vice
versa.
[0035] The stent 100 includes at least one bridge 26 configured to
connect one circumferential section 20 to an axially-spaced
adjacent circumferential section 20. The bridge 26 extends
generally circumferentially around the axis 16 on a generally
orthogonal plane with respect to the axis 16. That is, the bridge
26 forms a circumferential connector or bridge member (i.e.,
"circumferential bridge") between circumferential sections 20 of
the helical winding 18. Preferably, there are a plurality of
bridges 26 interconnecting the circumferential sections 20 to
adjacent circumferential sections 20.
[0036] As illustrated in FIG. 3, in the intermediate portion 14,
each circumferential section 20 includes a plurality of struts 28
joined together by strut vertices 30 and bridge vertices 31
disposed at ends of the struts 28. The strut vertices 30 connect
two struts 28 together, and the bridge vertices 31 connect one or
two struts 28 and a bridge 26 together. The bridge vertices 31 are
larger than the strut vertices 30 in order to accommodate the
connection of the bridges 26 to the struts 28. The bridges 26
connect the bridge vertices 31 in one circumferential section 20 to
the bridge vertices 31 in an adjacent circumferential section 20.
The bridges 26 provide a circumferential offset, equal to the
length of the bridge 26, between connected bridge vertices 31 that
approximately face each other across the spacing 22 between
adjacent circumferential sections 20. Upon expansion of the stent
100, the bridges 26 maintain an offset orientation between the
bridge vertices 31, so that the strut vertices 30 and bridge
vertices 31 of one circumferential section 20 do not abut or near
the opposing strut vertices 30 or bridge vertices 31 of an adjacent
circumferential section 20. Also, when the stent 100 is bent
slightly and forced to conform to a curve, the strut vertices 30
and bridge vertices 31 disposed on the inside path of the curve
will move towards each other and close the spacing 22 between
adjacent circumferential sections 20 (and possibly continue moving
towards each other so that one circumferential section 20 moves
into the path of the helical winding 18 occupied in part by another
circumferential section 20), but avoid or minimize direct contact
or interference because the bridges 26 cause the strut vertices 30
and bridge vertices 31 of one circumferential section 20 to
interdigitate with those of another circumferential section 20.
This interdigitation of the circumferential sections 20 allows the
stent 100 to bend easily without interference between struts 28,
strut vertices 30, and bridge vertices 31 on adjacent
circumferential sections 20 of the helical winding 18. That is,
each of the bridges 26 is configured so that the end of the bridge
26 connected to one bridge vertex 31 is circumferentially aligned
with the other end of the bridge 26 connected to another bridge
vertex 31 on a plane that is orthogonal to the axis 16, whether the
stent 100 is in an expanded or unexpanded configuration. As
illustrated in FIG. 3A, an alternative bridge 27a can be
non-linear, but one end of the bridge 27b remains circumferentially
aligned with the other end of the bridge 27c (illustrated by a
dashed line between bridge ends 27b and 27c) in a plane orthogonal
to the axis 16. As such, the bridge 26 is not required to be linear
as illustrated herein but can include curved, zig-zag, meandering
curves, sinusoidal, or curvilinear configurations as long as the
end points connecting to opposing bridge vertices 31 are aligned
with the circumference of a tube defined by the stent 100.
Alternatively, as illustrated in FIG. 3A, the bridges 26 of the
various embodiments can also provide an extension 27d that permits
comparatively slight extension of the stent 100 in the direction of
the axis 16 or beyond the radial periphery of the stent 100 defined
by the expansion of the circumferential sections 20, as described
and shown in U.S. Publication No. 2006/0060266; U.S. Pat. No.
7,763,067; U.S. Publication No. 2006/0074480; U.S. Pat. No.
7,780,721; and U.S. Publication No. 2006/0064155, all of which are
incorporated by reference herein in their entirety.
[0037] While providing these aforementioned advantages, the
circumferential bridges 26 provide for a more generally even
expansion of the stent 100 because some of the bridges 26 are
disposed away from the expanding portions of the circumferential
sections 20 that define the helical winding 18. As illustrated in
FIG. 3, in the preferred embodiments, the circumferential sections
20 have undulations that are formed by the generally linear struts
28 coupled together at the strut vertices 30 or bridge vertices 31,
which are deformed during expansion and compression of the stent
100. Where the bridge 26a is coupled to struts 28a and 28b in FIG.
3, the bridge vertex 31a is sufficiently rigid so that it isolates
any deformation of the struts 28a and 28b (during expansion of the
stent 100, for example) from the bridge 26a, so that bridge 26a is
not or only minimally deformed. Preferably, the stent 100 is a
Nitinol self-expanding stent of approximately 6 mm final diameter,
and the bridge 26 is approximately 100 microns wide in the
direction of the axis 16, approximately 200 microns thick in the
radial direction from the axis 16, and approximately 130 microns
long in the circumferential direction between the bridge vertices
31. The bridge vertices 31, illustrated in FIG. 4, are
approximately 90 microns wide in the direction of axis 16,
approximately 200 microns thick in the radial direction from the
axis 16, and approximately 1500 microns long in the circumferential
direction around axis 16. Other materials can be used instead of
Nitinol, such as, for example, weak shape memory metals (e.g.,
stainless steel, platinum, Elgiloy), shape memory polymers,
bioresorbable metals and polymers.
[0038] Referring to FIGS. 1 and 2, it is noted that the number of
bridges 26 and struts 28 can be varied. In one embodiment, the
number of struts 28 above and below any bridges 26 (within a single
arcuate undulation section 32) can be the same. An arcuate
undulation section 32 is a series of struts 28 and strut vertices
30 extending between two bridge vertices 31 on a single
circumferential section 20. For example, with reference to
circumferential section 20c in FIG. 1, bridge vertices 31a and 31b
have five struts 28 therebetween (which define five undulations in
the arcuate undulation section 32a). Bridges 26c and 26d join the
arcuate undulation section 32a to arcuate undulation sections 32 in
adjacent circumferential sections 20b and 20d, respectively, which
are spaced at a predetermined distance (spacing 22) from
circumferential section 20c. In particular, five struts 28 are
disposed along any one of the arcuate undulation sections 32
between any one bridge 26 and another next bridge 26 in the
intermediate portion 14, in a circumferential direction that is
either clockwise or counter-clockwise around the axis 16. It is
believed that a design having equal number struts 28 provides
advantageous characteristics with regard to flexibility and
strength. In the preferred embodiments, the number of struts 28 in
the clockwise or counterclockwise circumferential directions can
range from three to nine, inclusive. Alternatively, the number of
struts 28 in one circumferential direction can be different from
the number of struts 28 in the other circumferential direction. For
example, as illustrated in FIG. 8, there are seven struts 28
disposed between bridge vertex 31c and bridge vertex 31d in the
circumferential counter-clockwise direction identified by arrow 34
and five struts 28 disposed between bridge vertex 31c and bridge
vertex 31e in the circumferential clockwise direction identified by
arrow 36. In the preferred embodiments, a pattern of three struts
28 in the counter-clockwise direction and five struts 28 in the
clockwise direction from a single bridge vertex 31 (a three-five
pattern), a five-five pattern, or a five-seven pattern are
utilized.
[0039] With reference to FIG. 7, a portion of the stent 100 is
shown in a compressed and unimplanted configuration. In order to
discuss the various features of the struts 28 and bridges 26, the
following definition of strut length is used. A "strut length" is
the length of a strut 28 from a center 38 of a radius of curvature
of one end of the strut 28 (at a strut vertex 30 or bridge vertex
31) to another center 38 of a radius of curvature located on the
other end of the strut 28 (at a strut vertex 30 or bridge vertex
31). As such, as illustrated in FIG. 7, the strut length of the
strut 28c (extending between two strut vertices 30) is strut length
40a, the strut length of the strut 28d (extending between a strut
vertex 30 and a portion 42 of a bridge vertex 31) is strut length
40b, and the strut length of strut 28e (extending between a strut
vertex 30 and a portion 43 of a bridge vertex 31) is strut length
40c. Portion 43 is disposed more closely to the bridge 26 than
portion 42. Using this definition, it can be seen that strut length
40c is greater than strut length 40b, and that strut length 40b is
greater than strut length 40a. In an alternative embodiment, the
strut lengths of sequential struts 28 in a circumferential section
20 can alternate between a relatively short strut 28 and a
relatively long strut 28 to allow for the axial advancement of the
helical winding 18.
[0040] Further, the use of bridges 26 to connect adjacent
circumferential sections 20 is not limited to the configuration
illustrated in the figures but can include other configurations
where the bridge 26 is on a plane obliquely intersecting the axis
16 or generally parallel to the axis 16. For example, as shown in
FIG. 10, an alternative stent 300 includes an axial bridge 44
extending substantially parallel with respect to the axis 16 of the
stent. Also illustrated is a wave type spring bridge 45 (e.g.,
curvilinear in profile), an oblique bridge 46 extending obliquely
with respect to an axis extending parallel to the axis 16, and a
long bridge 47 extending far enough between bridge vertices 31 so
that there is a "bypassed" strut vertex 30 or another bridge vertex
passed by and not engaged with the long bridge 47. As also
illustrated in FIG. 10, the stent 300 can utilize a combination of
bridge types. Alternatively, the bridges 26, 44, 45, 46, or 47 can
directly connect a peak 48 of one circumferential section 20 to
another peak 48 of an adjacent circumferential section, as
illustrated by oblique bridge 46. In yet another alternative, the
bridges 26, 44, 45, 46, or 47 can connect a peak 48 to a trough 50
of an adjacent circumferential section 20, as illustrated by axial
bridge 44 and wave type spring bridge 45. In a further alternative,
the bridges 26, 44, 45, 46, or 47 can connect a trough 50 to a
trough 50, as illustrated by long bridge 47. Moreover, the
undulations of the arcuate undulation section 32 can be wave-like
in pattern. The wave-like pattern can also be generally sinusoidal
in that the pattern can have the general form of a sine wave,
whether or not such wave can be defined by a mathematical function.
Alternatively, any wave-like form can be employed so long as it has
amplitude and displacement. For example, a square wave, saw tooth
wave, or any applicable wave-like pattern defined by the struts
where the struts have substantially equal lengths or unequal
lengths. Also the stents 100, 200, 300, or 400 can be stents that
are bare, coated, covered, encapsulated, bio-resorbable or any
portion of such stents.
[0041] It is appreciated that the struts 28 and circumferential
sections 20 in the intermediate portion 14 of the stent 100 are
supported directly or indirectly on both axial sides (the sides
facing spacing 22) by bridges 26 because they fall between other
adjacent circumferential sections 20. However, the axially endmost
turns of the helical winding 18 (the axially endmost
circumferential sections 20, such as circumferential section 20a in
FIG. 1) are supported by bridges 26 only on the side of the
circumferential section 20 facing another circumferential section
20, and these endmost circumferential sections 20 lack bridges 26
on the sides that do not face an adjacent circumferential section
20, which can affect the proper and even orientation of the struts
28 in these endmost circumferential sections 20 during the
contraction or expansion of the stent 100. Any distortions
attributable to this one-sided bridge 26 arrangement are small and
are usually negligible. However, when markers are attached to the
endmost turns of the winding 18 (the endmost circumferential
sections 20) with extensions, the lengths of the markers and the
extensions are believed to amplify any distortion of the endmost
turns. This unevenness is particularly noticeable in a helical
winding because the struts are generally of unequal length in order
to provide a square-cut end to the stent, and any small distortions
of the endmost turns are amplified to differing degrees by the
different lengths of marker extensions.
[0042] There are several effects of the marker movement referred to
above. Cosmetically, the stent can be given a non-uniform
appearance that is objectionable to a clinician. If the distortions
are large enough, there can be interference between or overlapping
of the markers. These distortions can arise during manufacture of
the stent, when the pre-form of a self-expanded stent is expanded
to its final size. Similar distortions can arise when a finished
stent is compressed for insertion into a delivery system, or when a
stent is in place in vivo but held in a partially-compressed shape
by the anatomy.
[0043] Referring to FIGS. 1-3 and particularly 5A-5B, at the first
end 10 and second end 12 of the stent 100 there are provided
markers 60 extending from the strut vertices 30 of the helical
winding 18 with extensions 61. Reinforcing or connecting structures
62 are formed in the stent pre-form (i.e., in the initial
manufacturing state of the stent 100) and stabilize the shape and
orientation of markers 60 during the expansion of the stent 100 and
during the manufacture of the stent 100. It is believed that these
connecting structures 62 serve the additional function of improving
the stability of the markers 60 when the stent 100 is collapsed for
the purpose of delivering the stent to a location within a living
body. Further, these connecting structures 62 are also believed to
improve the stability of the stent 100 in vivo by improving the
resistance to deformation of the markers 60.
[0044] With the use of the connecting structures 62, the
distortions at the ends 10 and 12 of the stent 100 can be reduced
or mostly eliminated. Specifically, the connecting structure 62 is
formed by an annular ring 64 that includes a series of end struts
66 and bending segments 68 (similar to the struts 28 and strut and
bridge vertices 30 and 31) and is connected between adjacent
markers 60 in order to present reactive forces to resist distortion
from the expansion and compression of the struts 28. Because these
end struts 66 are connected at an axially outer end of the markers
60, they present the greatest possible leverage to maintain the
longitudinal axial alignment of the markers 60 and extensions 61
while presenting radial compressive and expansion forces similar to
those of the struts 28. These end struts 66 are cut into the stent
pre-form at the same time that the strut 28 and bridge 26 pattern
of the stent 100 is cut, typically using a laser cutting apparatus
or by a suitable forming technique (e.g., etching or EDM). These
end struts 66 (along with bending segments 68) then tend to hold
the markers 60 and the extensions 61 in parallel or generally in
longitudinal axial alignment with the axis 16 when the stent
pre-form is expanded during the manufacturing process.
[0045] Once the stent pre-form has been expanded, the end struts 66
can be either removed or left in place to form part of the finished
stent 100. If it is desired to remove the end struts 66, then the
end struts 66 can be designed with sacrificial points, i.e., there
can be notches or other weakening features in the body of the end
struts 66 where the end struts 66 attach to the markers 60, so that
the end struts 66 can be easily removed from the stent 100 by
cutting or breaking the end struts 66 at the sacrificial
points.
[0046] Alternatively, the end struts 66 can be designed so that
they remain part of the stent 100. In this case, there would be no
artificially weakened sacrificial point at the connection to the
markers 60. After the stent pre-form is expanded, the final
manufacturing operations would be completed, including cleaning,
heat-treating, deburring, polishing, and final cleaning or coating.
The resulting stent can then have the end struts 66 in place as an
integral part of the stent 100 structure.
[0047] In the preferred embodiment, shown in FIGS. 5A and 5B, the
markers 60 are approximately 620 microns wide in the
circumferential direction and approximately 1200 microns long in
the direction of axis 16. Most preferably, the markers 60 are
unitary with the extension 61 of the helical winding 18, are
generally rectangular in configuration, and can have the inside
surface of each marker 60 curved to conform to the tubular form of
the stent 100. Alternatively, the markers 60 can be formed as
spoon-shaped markers joined to the extensions 61 by welding,
bonding, soldering or swaging to portions or ends of the extensions
61. In a further alternative, materials can be removed from either
the luminal or abluminal surface of the markers 60 to provide a
void, and a radiopaque material can be joined to or filled into the
void. The markers 60 can be mounted at the end of extensions 61.
The end struts 66 joining the markers 60 can be approximately 80
microns wide in the circumferential direction and approximately
1500 microns long in the direction of the axis 16 when the stent
100 is in a compressed state, as illustrated in FIG. 5B. In the
embodiment illustrated in FIGS. 5A and 5B, there are four end
struts 66 between two adjacent markers 60. In the preferred
embodiments, the rectangular marker 60 can have its length
extending generally parallel to the axis 16 and its circumferential
width being greater than two times the width of any strut 28 (i.e.,
circumferential width in the compressed configuration). In one
embodiment, the circumferential width of at least one strut 28 is
approximately 65 microns and the circumferential width of the at
least one strut 28 is approximately 80-95% of a width of the bridge
26 in the direction of the axis 16.
[0048] Referring to FIG. 5B, the structure of the end struts 66
that connect to the markers 60 are preferably provided with a
slight curvature 70 (and corresponding curvature on the markers 60)
to provide for strain relief as the end struts 66 are expanded.
[0049] In an alternative embodiment, the connecting structure 62
includes two end struts 66 (instead of the four of the preferred
embodiment) of approximately 90 microns wide in the circumferential
direction (when the stent 100 is in the compressed configuration)
and approximately 2000 microns long in the direction of the axis
16. It should be noted that four end struts 66 can be utilized
when, for example, no marker 60 is used or only a minimal number of
markers 60 are needed. The markers 60 in the embodiments are
preferably approximately 620 microns wide in the circumferential
direction and approximately 1200 microns long in the direction of
the axis 16. The markers 60 are preferably mounted on the
extensions 61 that are approximately 200 microns wide in the
circumferential direction and approximately 2000 microns long in
the direction of the axis 16. Preferably, the stent 100, in the
form of a bare stent, is manufactured from Nitinol tubing
approximately 200 microns thick and having an approximate 1730
micron outside diameter, and is preferably designed to have an
approximately 6 mm finished, expanded, and unimplanted outside
diameter.
[0050] There are several features of the stent 100 that are
believed to be heretofore unavailable in the art. Consequently, the
state of the art is advanced by virtue of these features, which are
discussed below.
[0051] First, as noted previously, the continuous helical winding
18 can have a plurality of circumferential sections 20. A plurality
of bridges 26 extend on a plane generally orthogonal with respect
to the axis 16 to connect the circumferential sections 20. By this
configuration of the circumferential bridges 26 for the helical
winding 18, a more uniform expansion of the stent 100 is
achieved.
[0052] Second, each of the circumferential sections 20 can be
configured as arcuate undulation sections 32 (FIGS. 1 and 2)
disposed about the axis 16. The arcuate undulation sections 32 can
have bridges 26 with struts 28 connected thereto so that the struts
28 connecting to the bridges 26 have a length greater than a length
of other struts 28 that are not connected directly to the bridges
26. With reference to FIG. 7, it is noted that the struts 28 can
have a strut length 40c that is greater than a strut length 40b,
and a strut length 40b that is greater than a strut length 40a.
[0053] Third, the bridge 26 can be connected to the adjacent
arcuate undulation section 32 at respective locations other than
the peaks 48 of the adjacent arcuate undulation section 32. For
example, as shown in FIG. 4, the bridge 26 has an axial width
selected so that the edges of the bridge 26 form an offset 71 that
sets the bridge 26 slightly back from the outermost edge 31f of the
bridge vertices 31. By virtue of such arrangement, distortion is
believed to be reduced in the struts 28, and substantially reduced
at the struts 28 connecting directly to the bridge vertices 31.
Specifically, FIG. 6 illustrates the increased bending strains
placed on the stressed struts 28f when the bridge 26 is stressed by
bending or by torsion of the stent 100. In the example illustrated
in FIG. 6, a clockwise force is applied in the direction of the
arrows 72 which results from the bending or torsion of the stent
100, and the greatest stresses are believed to be developed at
high-stress points 76 where the stressed struts 28f connect to the
bridge vertices 31. It is believed that distortion of the strut
pattern can be expected to result in increased local strains, which
can cause small regions of the strut pattern to experience higher
than normal strains. It is also believed that such increased
strains can lead to premature failure in vivo. Because the
high-stress points 76 in the preferred embodiments are located away
from the bridge 26 by a distance corresponding to the
circumferential width of the bridge vertex 31, as illustrated in
FIG. 6, localized strains at the bridge 26 connecting points 74
(where the bridge 26 connects to the bridge vertices 31) are less
than those experienced at the high-stress points 76. In addition,
the struts 28 can have linear segments, curved segments or a
combination of curved and linear segments. Also, by virtue of the
circumferential bridges 26, the struts 28 can have a curved
configuration between peaks 48 of a winding 18 as illustrated, for
example, in FIG. 6.
[0054] Fourth, in the embodiment where a bridge 26 extends on a
plane generally orthogonal with respect to the axis 16, there is at
least one annular ring 64 connected to one of the first and second
ends 10 and 12 of the continuous helical winding 18. The annular
ring 64 is believed to reduce distortions to the markers 60
proximate the end or ends of the helical winding 18.
[0055] Fifth, in the preferred embodiment, where the stent 100
includes a continuous helical winding 18 and a plurality of
circumferential sections 20 defining a tube having an axial length
of about 60 millimeters and an outer diameter of about 6
millimeters, at least one bridge 26 is configured to connect two
circumferential sections 20 together so that the force required to
displace a portion of the stent 100 between two fixed points
located about 30 millimeters apart is less than 3.2 Newton for a
displacement of about 3 millimeters along an axis orthogonal to the
axis 16 of the stent 100. In particular, as illustrated in FIG. 9,
the stent 100 is loaded in carrier sheaths 80 made of PEBAX, where
the stent 100 is supported by an inner catheter 82 and outer
catheter 84. The outer catheter 84 has an inner diameter of about
1.6 millimeters. Both the inner and outer catheters 82 and 84 are
commercially available 6 French catheters under the trade name
Luminexx.RTM. III manufactured by Angiomed GmbH & Co.,
Medizintechnik KG of Germany, and available from C.R. Bard, Inc. of
Murray Hill, N.J. The two catheters 82 and 84 with the stent 100 in
between are placed on a 3-point bending jig where the outer
catheter 84 is supported at two locations spaced apart at distance
L of about 30 millimeters. A load F1 is placed on the stent 100
proximate the center of the distance L and the force required to
bend the catheters 82 and 84 and the stent 100 over a displacement
D1 of about 3 millimeters is measured. For the stent 100 of the
preferred embodiment illustrated in FIG. 1, the force required to
achieve a displacement D1 of 3 millimeters is less than 3.2
Newtons. As compared with a known helical stent (sold under the
trade name Lifestent.RTM. and having an outer diameter of
approximately 6 millimeters and a length of about 40 millimeters),
using the same testing configuration, the force required to
displace the known stent in a Luminexx.RTM. III catheter sheath
over a distance D1 of approximately 3 millimeters is approximately
3.2 Newtons or greater. It is believed that the lower the force
required to displace the stent (when contained in catheters 82 and
84) a distance D1 (of about 3 millimeters), the better the ability
of the stent and the catheters to navigate tortuous anatomy. By
requiring less than 3.2 Newtons force in this test, the preferred
embodiment stent 100 is believed to be highly flexible during
delivery and implantation, as compared to known stents and delivery
systems, and this high flexibility facilitates the ability of the
clinician to navigate a duct or vessel necessary to deliver and
implant the stent. In the particular embodiment tested, the force
F1 for stent 100 was approximately 1.7 Newtons for a 6 French
Luminexx.RTM. III catheter.
[0056] Sixth, by virtue of the structures described herein, an
advantageous technique to load a helical stent 100 is provided that
does not have physical interference between arcuate undulation
sections 32 and bridges 26 in the compressed configuration of the
stent 100 in a generally tubular sheath from an inside diameter of
approximately 6 millimeters to the compressed stent 100
configuration of approximately 2 millimeters (6 French).
Specifically, where a stent is utilized with approximately 48
arcuate undulation sections 32 (which include the struts 28) in
each circumferential section 20, and 9 bridges 26 for connection to
adjacent circumferential sections 20, it has been advantageously
determined that the stent 100 does not require a transition portion
and a tubular end zone, as is known in the art. In particular, the
method can be achieved by utilization of a physical embodiment of
the stent 100 (e.g., FIGS. 1-5) and compressing the stent 100. The
stent 100 has an outside diameter of approximately 6 millimeters
that must be compressed to fit within the generally tubular sheath
80 that has an outside diameter of approximately 2 millimeters (6
French) and an inside diameter of approximately 1.6 millimeters,
without any of the struts 28 of the stent 100 crossing each other
when compressed and inserted into the sheath 80. In other words, in
the expanded unimplanted configuration of the stent 100, none of
the struts 28 and bridges 26 physically interfere with, i.e.,
overlap or cross, other struts 28 or bridges 26 of the stent 100.
The stent 100 can be compressed, without the use of transition
strut segments (or the use of the annular rings 64) at the axial
ends of the helical winding 18, to a smaller outer diameter of
about 3 millimeters or less (and preferably less than 2
millimeters) where the inner surfaces of the struts 28 and bridges
26 remain substantially contiguous without physical interference of
one strut 28 with another strut 28 or with a bridge 26.
[0057] Bio-active agents can be added to the stent (e.g., either by
a coating or via a carrier medium such as resorbable polymers) for
delivery to the host vessel or duct. The bioactive agents can also
be used to coat the entire stent. A coating can include one or more
non-genetic therapeutic agents, genetic materials and cells and
combinations thereof as well as other polymeric coatings.
[0058] Non-genetic therapeutic agents include anti-thrombogenic
agents such as heparin, heparin derivatives, urokinase, and PPack
(dextrophenylalanine proline arginine chloromethylketone);
anti-proliferative agents such as enoxaprin, angiopeptin, or
monoclonal antibodies capable of blocking smooth muscle cell
proliferation, hirudin, and acetylsalicylic acid; anti-inflammatory
agents such as dexamethasone, prednisolone, corticosterone,
budesonide, estrogen, sulfasalazine, and mesalamine;
antineoplastic/antiproliferative/anti-miotic agents such as
paclitaxel, 5-fluorouracil, cisplatin, vinblastine, vincristine,
epothilones, endostatin, angiostatin and thymidine kinase
inhibitors; anesthetic agents such as lidocaine, bupivacaine, and
ropivacaine; anti-coagulants, an RGD peptide-containing compound,
heparin, antithrombin compounds, platelet receptor antagonists,
anti-thrombin anticodies, anti-platelet receptor antibodies,
aspirin, prostaglandin inhibitors, platelet inhibitors and tick
antiplatelet peptides; vascular cell growth promotors such as
growth factor inhibitors, growth factor receptor antagonists,
transcriptional activators, and translational promotors; vascular
cell growth inhibitors such as growth factor inhibitors, growth
factor receptor antagonists, transcriptional repressors,
translational repressors, replication inhibitors, inhibitory
antibodies, antibodies directed against growth factors,
bifunctional molecules consisting of a growth factor and a
cytotoxin, bifunctional molecules consisting of an antibody and a
cytotoxin; cholesterol-lowering agents; vasodilating agents; and
agents which interfere with endogenous vascoactive mechanisms.
[0059] Genetic materials include anti-sense DNA and RNA, DNA coding
for, anti-sense RNA, tRNA or rRNA to replace defective or deficient
endogenous molecules, angiogenic factors including growth factors
such as acidic and basic fibroblast growth factors, vascular
endothelial growth factor, epidermal growth factor, transforming
growth factor alpha and beta, platelet-derived endothelial growth
factor, platelet-derived growth factor, tumor necrosis factor
alpha, hepatocyte growth factor and insulin like growth factor,
cell cycle inhibitors including CD inhibitors, thymidine kinase
("TK") and other agents useful for interfering with cell
proliferation the family of bone morphogenic proteins ("BMPs"),
BMP-2, BMP-3, BMP-4, BMP-5, BMP-6 (Vgr-1), BMP-7 (OP-1), BMP-8,
BMP-9, BMP-10, BMP-1, BMP-12, BMP-13, BMP-14, BMP-15, and BMP-16.
Desirable BMP's are any of BMP-2, BMP-3, BMP-4, BMP-5, BMP-6 and
BMP-7. These dimeric proteins can be provided as homodimers,
heterodimers, or combinations thereof, alone or together with other
molecules. Alternatively or, in addition, molecules capable of
inducing an upstream or downstream effect of a BMP can be provided.
Such molecules include any of the "hedgehog" proteins, or the DNAs
encoding them.
[0060] Cells can be of human origin (autologous or allogeneic) or
from an animal source (xenogeneic), genetically engineered if
desired to deliver proteins of interest at the deployment site. The
cells can be provided in a delivery media. The delivery media can
be formulated as needed to maintain cell function and
viability.
[0061] Suitable polymer coating materials include polycarboxylic
acids, cellulosic polymers, including cellulose acetate and
cellulose nitrate, gelatin, polyvinylpyrrolidone, cross-linked
polyvinylpyrrolidone, polyanhydrides including maleic anhydride
polymers, polyamides, polyvinyl alcohols, copolymers of vinyl
monomers such as EVA, polyvinyl ethers, polyvinyl aromatics,
polyethylene oxides, glycosaminoglycans, polysaccharides,
polyesters including polyethylene terephthalate, polyacrylamides,
polyethers, polyether sulfone, polycarbonate, polyalkylenes
including polypropylene, polyethylene and high molecular weight
polyethylene, halogenated polyalkylenes including
polytetrafluoroethylene, polyurethanes, polyorthoesters, proteins,
polypeptides, silicones, siloxane polymers, polylactic acid,
polyglycolic acid, polycaprolactone, polyhydroxybutyrate valerate
and blends and copolymers thereof, coatings from polymer
dispersions such as polyurethane dispersions (for example,
BAYHDROL.RTM. fibrin, collagen and derivatives thereof,
polysaccharides such as celluloses, starches, dextrans, alginates
and derivatives, hyaluronic acid, squalene emulsions. Polyacrylic
acid, available as HYDROPLUS.RTM. (from Boston Scientific
Corporation of Natick, Mass.), and described in U.S. Pat. No.
5,091,205, the disclosure of which is hereby incorporated herein by
reference, is particularly desirable. Even more desirable is a
copolymer of polylactic acid and polycaprolactone.
[0062] The preferred stents can also be used as the framework for a
vascular graft. Suitable coverings include nylon, collagen, PTFE
and expanded PTFE, polyethylene terephthalate, KEVLAR.RTM.
polyaramid, and ultra-high molecular weight polyethylene. More
generally, any known graft material can be used including synthetic
polymers such as polyethylene, polypropylene, polyurethane,
polyglycolic acid, polyesters, polyamides, their mixtures, blends
and copolymers.
[0063] In the preferred embodiments, some or all of the bridges 26
can be bio-resorbed while leaving the undulating strut 28
configuration essentially unchanged. In other embodiments, however,
the entire stent 100 can be resorbed in stages by a suitable
coating over the resorbable material. For example, the bridges 26
can resorb within a short time period after implantation, such as,
for example, 30 days. The remaining helical stent framework (made
of a resorbable material such as metal or polymers) can thereafter
resorb in a subsequent time period, such as, for example, 90 days
to 2 years from implantation.
[0064] Markers 60 can be provided for all of the embodiments
described herein. The marker 60 can be formed from the same
material as the stent 100 as long as the material is radiographic
or radiopaque. The marker material can also be formed from gold,
tantalum, platinum for example. The marker 60 can be formed from a
marker material different from the material used to form another
marker 60.
[0065] The stents described herein can be, with appropriate
modifications, delivered to an implantation site in a host with the
delivery devices described and shown in U.S. Patent Publication
Nos. 2005/0090890 or 2002/0183826, U.S. Pat. Nos. 6,939,352 or
6,866,669.
[0066] Although the preferred embodiments have been described in
relation to a frame work that define a tube using wire like
members, other variations are within the scope of the invention.
For example, the frame work can define different tubular sections
with different outer diameters, the frame work can define a tubular
section coupled to a conic section, the frame work can define a
single cone, and the wire-like members can be in cross-sections
other than circular such as, for example, rectangular, square, or
polygonal.
[0067] Even though various aspects of the preferred embodiments
have been described as self-expanding Nitinol stents suitable for
use in the common bile duct or superficial femoral artery, it
should be apparent to a person skilled in the art that these
improvements can be applied to self-expanding stents of all sizes
and made from any suitable material. Further, such stents can be
applied to any body lumen where it is desired to place a structure
to maintain patency, prevent occlusive disease, or for other
medical purposes, such as to hold embolization devices in place.
Further, the features described in the embodiments can be applied
to balloon-expanded stents made from malleable or formable
materials and intended to be expanded inside a suitable body lumen.
The features described in the embodiments can also be applied to
bare metal stents, stents made from other than metallic materials,
stents with or without coatings intended for such purposes as
dispensing a medicament or preventing disease processes, and stents
where some or all of the components (e.g., struts, bridges,
paddles) of the stents are bio-degradable or bio-resorbable.
[0068] The embodiments use the example of a 6 mm self-expanding
stent, but can be applied with equal merit to other kinds of stents
and stents of other sizes. Specifically, stents for use in
peripheral arteries are customarily made in outer diameters ranging
from 3 mm to 12 mm, and in lengths from 10 mm to 200 mm. Stents of
larger and smaller diameters and lengths can also be made
accordingly. Also, stents embodying the features of the embodiments
can be used in other arteries, veins, the biliary system,
esophagus, trachea, and other body lumens.
[0069] In the embodiment illustrated in FIG. 1, the stent 100
includes the first end 10, the second end 12, and the intermediate
portion 14, each surrounding the axis 16. The intermediate portion
14 includes the helical winding 18, and the first end 10 and second
end 12 each include the annular ring 64. As illustrated in FIG. 1,
the helical winding 18 of the stent 100 is disposed at an angle
(the helical angle 24) to the axis 16, i.e., a plane defined by the
struts 28 of the winding 18 is at a non-orthogonal angle to the
axis 16. As also illustrated in FIG. 1, the annular rings 64 of the
stent 100 are orthogonal to the axis 16, i.e., a plane defined by
the end struts 66 of the annular ring 64 is orthogonal to the axis
16. These differing geometries (helical and orthogonal) of the
helical winding 18 and the annular rings 64 are connected together
by the extensions 61, which extend between the winding 18 and
annular ring 64, or by direct connection without an extension 61
where the winding 18 and annular ring 64 are disposed proximate to
each other, as illustrated in FIG. 1 at the last strut 28g. The
last strut 28g is the final strut 28 in the series of struts 28 of
the helical winding 18, and there is a last strut 28g proximate the
first end 10 and a last strut 28g proximate the second end 12.
[0070] In a preferred embodiment illustrated in FIGS. 11 and 12,
the annular ring 64 of the stent 400 includes extensions 461 that
extend in the direction of the axis 16 and connect with the strut
vertices 30 of the longitudinally endmost portions of the winding
418. As illustrated in FIGS. 11 and 13, the extensions 461
preferably connect to every fourth or fifth end-facing strut vertex
30 so that there are eight or ten struts 28 disposed between the
points where the five extensions 461 connect to the strut vertices
30 at the longitudinal end of the helical winding 418. It is
believed that the use of five extensions, rather than six or more,
advantageously provides an annular ring 64 that can be compressed
to a smaller diameter (in the compressed orientation of the stent)
than the compressed diameter that can be achieved a six-extension
stent. This is because the extensions form the
circumferentially-widest portions of the annular ring 64. A smaller
compressed diameter provides a smaller compressed-stent profile
that advantageously aids in loading the compressed stent into a
delivery device, and facilitates the placement of the compressed
stent in small anatomical passages.
[0071] As also illustrated in FIGS. 11 and 13, the last strut 28g
in the helical winding 418 differs (from the other struts 28 that
connect to an extension 461) because the last strut 28g is
connected to an extension 461a that extends farther from the
annular ring 64 than the other extensions 461 and because the last
strut 28g connects to join a modified bridge 426 with the
corresponding extension 461a. FIG. 13 is a view of the stent 400 of
FIGS. 11 and 12, but with the stent 400 displayed as if it had been
longitudinally cut and laid out in the extended orientation upon a
flat plane. As illustrated in FIG. 13, the modified bridge 426 is
similar to the bridges 26, but one side of the bridge 426 is
connected to an end of the extension 461a.
[0072] FIG. 13 also illustrates that certain struts 28 (extension
struts 28h) in the endmost circumferential section 420a can have
strut lengths that varying in order to allow connection between the
extension 461 while maintaining the helical form and spacing 22 of
the helical winding 418. As illustrated in FIG. 13, the extension
struts 28h can be either longer than or short than the other struts
28 of the stent 400. Furthermore, the extension struts 28h extend
these shorter or longer lengths so that the end of the struts 28h
extending away from the extensions 461 connect to strut vertices 30
or bridge vertices 31 disposed in line with the spacing 22 defined
by the helical winding 418. The variable strut lengths of the
extension struts 28h serve, in part, as alignment structures to
align extensions 461, which are preferably distributed in a pattern
of five equally-distributed locations on the circumference of the
annular ring 64, with corresponding strut vertices 30 or the bridge
426 (as illustrated in FIG. 13), which do not always naturally
align with the circumferential locations of the extensions 461.
[0073] In the embodiment of FIGS. 11-13, the pattern of bridges 26
and struts 28 over the length of the helical winding 418 (i.e., the
strut pattern) varies from the end strut 28g proximate the first
end 10 to the end strut 28g proximate the second end 12. As
illustrated in FIGS. 11 and 13, the strut pattern in the majority
of the helical winding 418 is preferably a five-seven pattern,
where the number of struts 28 between sequential bridges 26 along
the path of the helical winding 418 is a repeating pattern of five
and seven, as illustrated at circumferential sections 420c, 420d,
and 420e. In the second-to-endmost winding of helical winding 418,
at circumferential section 420b, the five-seven pattern preferably
changes to a variable pattern of four, three, and one, where
additional bridges 26 are added to the stent 400 between
circumferential sections 420b and 420a. In the endmost winding of
the helical winding 418, at circumferential section 420a, the strut
pattern preferably changes again to a four-four pattern where four
struts 28 are provided between bridges 26 along the helical path of
the circumferential section 420a. In the embodiment illustrated in
FIGS. 11-13, the strut 400 can be characterized as having a
five-seven pattern with a four-four pattern at each end of the
stent 400 where connecting to the first and second ends 10 and 12.
As can be appreciated, alternative strut patterns can be employed,
with the majority of the intermediate portion 14 having one strut
pattern and each end of the intermediate portion 14 having a
different pattern, with a single circumferential section 420
disposed between two adjoining patterns to act as a transition
between the two strut patterns. The circumferential section 420b
preferably acts as a transition between the five-seven pattern and
the four-four pattern and thus has a variable pattern that is
adjusted to accommodate the transition between alternative
adjoining patterns.
[0074] It is believed that greater stent flexibility is achieved in
the portions of the stent 400 having more struts 28 disposed
between bridges 26 (a higher-numbered strut pattern, preferably a
five-seven pattern) than in portions having fewer struts 28 between
bridges 26 (a lower-numbered strut pattern, preferably a four-four
pattern). It is also believed that the ends of the stent 400 are
less flexible than the longitudinal middle of the stent 400 because
of the additional stiffness provided where the strut pattern
changes from high-numbered strut pattern to a lower-numbered strut
pattern, preferably changing from a five-seven pattern to a
four-four pattern.
[0075] While the present invention has been disclosed with
reference to certain embodiments, numerous modifications,
alterations, and changes to the described embodiments are possible
without departing from the sphere and scope of the present
invention, as defined in the appended claims. Accordingly, it is
intended that the present invention not be limited to the described
embodiments, but that it has the full scope defined by the language
of the following claims, and equivalents thereof.
* * * * *