U.S. patent application number 10/389273 was filed with the patent office on 2003-12-11 for stent.
Invention is credited to Thompson, Paul J..
Application Number | 20030229391 10/389273 |
Document ID | / |
Family ID | 25074316 |
Filed Date | 2003-12-11 |
United States Patent
Application |
20030229391 |
Kind Code |
A1 |
Thompson, Paul J. |
December 11, 2003 |
Stent
Abstract
The present disclosure relates to a stent including a stent body
having a stent axis. The stent body includes structural members
defining openings through the stent body. The structural members
are provided with regions having different widths. The relative
sizes of the widths are selected to control the length of the stent
body as the stent body is radially expanded from an un-deployed
orientation to a deployed orientation. In one embodiment, the
regions having different widths are provided by tapering the widths
of selected segments of the structural member.
Inventors: |
Thompson, Paul J.; (New
Hope, MN) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Family ID: |
25074316 |
Appl. No.: |
10/389273 |
Filed: |
August 14, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10389273 |
Aug 14, 2003 |
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09765725 |
Jan 18, 2001 |
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6558415 |
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09765725 |
Jan 18, 2001 |
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09545810 |
Apr 7, 2000 |
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6358274 |
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09545810 |
Apr 7, 2000 |
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09049486 |
Mar 27, 1998 |
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6132460 |
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Current U.S.
Class: |
623/1.17 |
Current CPC
Class: |
A61F 2002/91508
20130101; A61F 2/915 20130101; A61F 2002/91558 20130101; A61F
2210/0014 20130101; A61F 2002/91575 20130101; A61F 2002/91541
20130101; A61F 2002/9155 20130101; A61F 2250/0036 20130101; A61F
2230/0013 20130101; A61F 2/89 20130101; A61F 2230/0054
20130101 |
Class at
Publication: |
623/1.17 |
International
Class: |
A61F 002/06 |
Claims
What is claimed is:
1. A stent comprising: a stent body having a stent axis; the stent
body including a structural member extending in an undulating
pattern about a circumference of the stent body; the structural
member including a plurality of segments that extend generally
longitudinally along the stent axis; and at least some of the
segments having widths that taper as the at least some segments
extend longitudinally along the stent axis.
2. The stent of claim 1, wherein a taper angle of the widths is
selected to minimize a length change of the stent body as the stent
body is radially expanded from an un-deployed orientation to a
deployed orientation.
3. The stent of claim 1, wherein the at least some segments include
pairs of tapered segments, the pairs of tapered segments being
interconnected by non-tapered segments.
4. The stent of claim 3, wherein the non-tapered segments are
skewed relative to the stent axis.
5. The stent of claim 1, wherein the segments are substantially
straight.
6. The stent of claim 1, wherein the stent body is made of a
shape-memory metal.
7. A stent comprising: a stent body having a stent axis; the stent
body including a plurality of cell structures defining a plurality
of cells; the cell structures including structural members that
extend in an undulating pattern about a circumference of the stent
body; the structural members including segments that extend
generally longitudinally along the stent axis; the structural
members including peaks and valleys; the cell structures being
interconnected at connection locations; at least some of the
segments extending from the connection locations to the peaks and
valleys; and the at least some segments having enlarged first
widths adjacent the connection locations as compared to smaller
second widths located adjacent the peaks and valleys.
8. The stent of claim 7, wherein the at least some of the segments
are provided with a narrowing width taper that extends between the
first and second widths.
9. The stent of claim 7, wherein the relative sizes of the first
and second widths are selected to minimize a length change of the
stent body as the stent body is radially expanded from an
un-deployed orientation to a deployed orientation.
10. The stent of claim 7, wherein the at least some segments
include pairs of tapered segments positioned at the connection
locations, the pairs of tapered segments being interconnected by
non-tapered segments.
11. The stent of claim 10, wherein the non-tapered segments are
skewed relative to the stent axis.
12. The stent of claim 7, wherein the segments are straight.
13. The stent of claim 7, wherein the connection locations include
longitudinal connection locations and circumferential connection
locations.
14. The stent of claim 13, wherein the cells are symmetrical about
first axes extending through the circumferential connection
locations, and the cells are also symmetrical about second axes
extending through the longitudinal connection locations.
15. A stent comprising: a stent body having a stent axis; the stent
body including a structural member extending in an undulating
pattern about a circumference of the stent body; the structural
member including peaks and valleys, and also including segments
that interconnect the peaks and valleys; and at least some of the
segments having widths that taper along lengths of the at least
some segments.
16. The stent of claim 15, wherein the segments are substantially
straight.
17. The stent of claim 15, wherein the structural members form cell
structures that are interconnected at connection locations, and
wherein the at least some segments have larger widths adjacent the
connection locations than adjacent the peaks and valleys.
18. The stent of claim 15, wherein a taper angle of the widths is
selected to control a length change of the stent body as the stent
body is radially expanded from an un-deployed orientation to a
deployed orientation.
19. The stent of claim 18, wherein the taper angle is selected to
minimize a length change of the stent body as the stent body is
expanded from the un-deployed orientation to the deployed
orientation.
20. A stent comprising: a stent body having a stent axis, the stent
body being radially expandable from a non-deployed orientation
having a first length to a deployed orientation having a second
length; the stent body including a structural member extending in
an undulating pattern about a circumference of the stent body; and
the first length being substantially equal to the second
length.
21. A method for making a stent, the method comprising:
constructing a stent body having a stent axis, the stent body
including structural members defining openings through the stent
body; and during construction of the stent body, providing at least
some of the structural members with regions having first and second
different widths, the relative sizes of the first and second widths
being selected to control a length of the stent body as the stent
body is radially expanded from an un-deployed orientation to a
deployed orientation.
22. The method of claim 21, wherein the relative sizes of the
widths are selected to minimize a length variation when the stent
body is radially expanded from the un-deployed orientation to the
deployed orientation.
23. The method of claim 21, further comprising providing the
structural members with a gradual taper in width between the first
and second widths.
24. The method of claim 23, wherein the segments are substantially
straight.
25. The method of claim 21, further comprising shape-setting the
stent body to an expanded diameter corresponding to the deployed
orientation after the stent body has been constructed.
26. The method of claim 21, wherein the structural members extend
in undulating patterns.
27. A stent comprising: a stent body that is radially expandable
from an un-deployed orientation to a deployed orientation; the
stent body including structural members defining openings through
the stent body; the structural members including segments having
first regions with enlarged widths and second regions with more
narrow widths; and the relative sizes of the enlarged widths and
the more narrow widths are selected to control a length of the
stent body as the stent body is expanded from the un-deployed
orientation to the deployed orientation.
28. The stent of claim 27, wherein the relative sizes of widths are
selected to minimize a change in the length of the stent body as
the stent body is expanded from the un-deployed orientation to the
deployed orientation.
29. The stent of claim 27, wherein widths of the segments gradually
taper between the enlarged widths and the more narrow widths.
30. The stent of claim 29, wherein the segments are substantially
straight between the first regions and the second regions.
31. The stent of claim 30, wherein between the first and second
regions, the segments extend in a generally longitudinal direction
relative to an axis of the stent.
Description
I.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation-in-part of
co-pending and commonly assigned U.S. patent application Ser. No.
09/545,810 which is a continuation of commonly assigned U.S. patent
application Ser. No. 09/049,486 filed Mar. 27, 1998, now U.S. Pat.
No. 6,132,460.
II.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention pertains to stents for use in intraluminal
applications. More particularly, this invention pertains to a novel
structure for such stents.
[0004] 2. Description of the Prior Art
[0005] Stents are widely used for numerous applications where the
stent is placed in the lumen of a patient and expanded. Such stents
may be used in coronary or other vasculature, as well as other body
lumens.
[0006] Commonly, stents are cylindrical members. The stents expand
from reduced diameters to enlarged diameters. Frequently, such
stents are placed on a balloon catheter with the stent in the
reduced-diameter state. So placed, the stent is advanced on the
catheter to a placement site. At the site, the balloon is inflated
to expand the stent to the enlarged diameter. The balloon is
deflated and removed, leaving the enlarged diameter stent in place.
So used, such stents are used to expand occluded sites within a
patient's vasculature or other lumen.
[0007] Examples of prior art stents are numerous. For example, U.S.
Pat. No. 5,449,373 to Pinchasik et al. teaches a stent with at
least two rigid segments joined by a flexible connector. U.S. Pat.
No. 5,695,516 to Fischell teaches a stent with a cell having a
butterfly shape when the stent is in a reduced-diameter state. Upon
expansion of the stent, the cell assumes a hexagonal shape.
[0008] In stent design, it is desirable for the stent to be
flexible along its longitudinal axis to permit passage of the stent
through arcuate segments of a patient's vasculature or other body
lumen. Preferably, the stent will have at most minimal longitudinal
shrinkage when expanded and will resist compressive forces once
expanded.
III.
SUMMARY OF THE INVENTION
[0009] The present disclosure relates to a stent including a stent
body having a stent axis. The stent body includes structural
members that define openings through the stent body. The structural
members are provided with regions having different widths. The
relative sizes of the widths are selected to control the length of
the stent body as the stent body is radially expanded from an
un-deployed orientation to a deployed orientation. In one
embodiment, the regions having different widths are provided by
tapering the widths of selected segments of the structural member.
In a preferred embodiment, the relative sizes of the widths are
selected to minimize or eliminate length changes as the stent body
is expanded from the un-deployed orientation to the expanded
orientation.
IV.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a perspective view of a first embodiment of a
stent according to the present invention shown in a rest diameter
state and showing a plurality of stent cells each having a major
axis perpendicular to an axis of the stent;
[0011] FIG. 2 is a plan view of the stent of FIG. 1 as it would
appear if it were longitudinally split and laid out flat;
[0012] FIG. 3 is the view of FIG. 2 following expansion of the
stent to an enlarged diameter;
[0013] FIG. 4 is a view taken along line 4-4 in FIG. 2;
[0014] FIG. 5 is a view taken along line 5-5 in FIG. 2;
[0015] FIG. 6 is an enlarged view of a portion of FIG. 2
illustrating a cell structure with material of the stent
surrounding adjacent cells shown in phantom lines;
[0016] FIG. 7 is the view of FIG. 2 showing an alternative
embodiment of the present invention with a cell having five peaks
per longitudinal segment;
[0017] FIG. 8 is the view of FIG. 2 showing an alternative
embodiment of the present invention with a major axis of the cell
being parallel to an axis of the stent; and
[0018] FIG. 9 is the view of FIG. 8 following expansion of the
stent to an enlarged diameter;
[0019] FIG. 10 is a plan view of another stent as it would appear
if it were longitudinally split and laid out flat;
[0020] FIG. 11 is an enlarged view of a portion of the stent of
FIG. 10; and
[0021] FIG. 12 is a plan view of a portion of the stent of FIG. 10
in a deployed/expanded orientation, the stent has been
longitudinally cut and laid flat.
V.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] Referring now to the several drawing figures in which
identical elements are numbered identically, a description of the
preferred embodiment of the present invention will now be provided.
Where several embodiments are shown, common elements are similarly
numbered and not separately described with the addition of
apostrophes to distinguish the embodiments.
[0023] FIG. 1 illustrates a stent 10 having a rest length L.sub.r
and an un-deployed or reduced diameter D.sub.r. For ease of
illustration, the stent 10 is shown flat in FIG. 2 which
illustrates a rest circumference C.sub.r (C.sub.r=.pi.D.sub.r). In
FIG. 2, locations A, B, C, D, E, F and G are shown severed from
their normally integrally formed locations A.sub.1, B.sub.1,
C.sub.1, D.sub.1, E.sub.1, F.sub.1 and G.sub.1. This permits the
stent 10 to be shown as if it were severed at normally integrally
formed locations A-A.sub.l, B-B.sub.1, C-C.sub.1, D-D.sub.1,
E-E.sub.l, F-F.sub.1 and G-G.sub.1 and laid flat. FIG. 6 is an
enlarged portion of the view of FIG. 2 to better illustrate a novel
cell structure as will be described. The stent 10 is a reticulated,
hollow tube. The stent 10 may be expanded from the rest diameter
D.sub.r (and corresponding rest circumference C.sub.r) to an
expanded or enlarged diameter. FIG. 3 is a view similar to FIG. 2
(i.e., illustrating the expanded stent 10 as it would appear if
longitudinally split and laid flat). Since FIG. 3 is a
two-dimensional representation, the enlarged diameter is not shown.
However, the enlarged circumference C.sub.e is shown as well as a
length L.sub.e following expansion. The expanded diameter is equal
to C.sub.e/.pi..
[0024] As will be discussed length L.sub.e is preferably not more
than minimally smaller (e.g., less than 10% smaller) than length
L.sub.r. Ideally, L.sub.e equals L.sub.r.
[0025] The material of the stent 10 defines a plurality of cells
12. The cells 12 are bounded areas which are open (i.e., extend
through the wall thickness of the stent 10). The stent 10 may be
formed through any suitable means including laser or chemical
milling. In such processes, a hollow cylindrical tube is milled to
remove material and form the open cells 12.
[0026] The cells 12 have a longitudinal or major axis
X.sub.M-X.sub.M and a transverse or minor axis X.sub.m-X.sub.m. In
the embodiments of FIGS. 1-3, the major axis X.sub.M-X.sub.M is
perpendicular to the longitudinal cylindrical axis X-X of the stent
10. In the embodiments of FIGS. 8 and 9, the major axis
X.sub.M'-X.sub.M' is parallel to the longitudinal cylindrical axis
X'-X' of the stent 10'. The cell 12 is symmetrical about axes
X.sub.M-X.sub.M and X.sub.m-X.sub.m.
[0027] The cell 12 is defined by portions of the tube material
including first and second longitudinal segments 14. The segments
14 each have a longitudinal axis X.sub.a-X.sub.a as shown in FIG.
6. The segments' longitudinal axes X.sub.a-X.sub.a are parallel to
and positioned on opposite sides of the cell major axis
X.sub.M-X.sub.M.
[0028] Each of longitudinal segments 14 has an undulating pattern
to define a plurality of peaks 17, 21, 25 and valleys 19, 23. The
peaks 17, 21, 25 are spaced outwardly from the longitudinal axes
X.sub.a-X.sub.a and the valleys 19, 23 are spaced inwardly from the
longitudinal axes X.sub.a-X.sub.a. As used in this context,
"inward" and "outward" mean toward and away from, respectively, the
cell's major axis X.sub.M-X.sub.M.
[0029] Each of the peaks 17, 21, 25 and valleys 19, 23 is a
generally semi-circular arcuate segment. The peaks 17, 21, 25 and
valleys 19, 23 are joined by parallel and spaced-apart straight
segments 16, 18, 20, 22, 24 and 26 which extend perpendicular to
the major axis X.sub.M-X.sub.M. Linearly aligned straight end
portions 16, 26 of opposing segments 14 are joined at first and
second longitudinal connection locations 27 spaced apart on the
major axis X.sub.M-X.sub.M. First and second transverse connection
locations 28 are spaced apart on the minor axis X.sub.m-X.sub.m.
The first and second transverse connection locations 28 are
positioned at the apices of the center peaks 21 of the longitudinal
segments 14.
[0030] Except as will be described, the segments 14 have uniform
cross-sectional dimensions throughout their length as illustrated
in FIG. 4. By way of non-limiting example, the width W and
thickness T of the straight line segments 16, 18, 20, 22, 24 and 26
are about 0.0065 inch (about 0.16 mm) and about 0.0057 inch (about
0.14 mm), respectively.
[0031] For reasons that will be described, the width W' (FIG. 5) at
the apices of the peaks 17, 21, 25 and valleys 19, 23 is narrower
than width W (in the example given, narrow width W' is about 0.0055
inch or about 0.13 mm). The width of the peaks 17, 21, 25 and
valleys 19, 23 gradually increases from width W' at the apices to
width W at the straight segments 16, 18, 20, 22, 24 and 26. At the
longitudinal and transverse connection locations 27, 28, the width
W.sub.C (shown in FIG. 2) is preferably equal to or less than the
common width W.
[0032] The combined lengths of segments 16-20 to the apex of peak
21 represent a path length 50 from longitudinal connection location
27 to transverse connection location 28. Similarly the combined
lengths of the other arcuate and straight segments 22-26 to the
apex of peak 21 represent identical length path lengths 51 of
identical geometry from longitudinal connection locations 27 to
transverse connection locations 28. Each of the path lengths 50, 51
is longer than a straight-line distance between the transverse and
longitudinal connection locations 27, 28. As will be described, the
straight-line distance between the transverse and longitudinal
connection locations 27, 28 increases as the diameter of the stent
10 is expanded. The path lengths 50, 51 are sized to be not less
than the expanded straight-line distance.
[0033] The stent 10 includes a plurality of identical cells 12.
Opposite edges of the segments 14 define obliquely adjacent cells
(such as cells 12.sub.1, 12.sub.2 in FIG. 2). Cells 12 having major
axes X.sub.M-X.sub.M collinear with the major axis X.sub.M-X.sub.M
of cell 12 are interconnected at the longitudinal connection
locations 27. Cells having minor axes collinear with the minor axis
X.sub.m-X.sub.m of cell 12 are interconnected at the transverse
connection locations 28.
[0034] As mentioned, the stent 10 in the reduced diameter of FIG. 1
is advanced to a site in a lumen. The stent 10 is then expanded at
the site. The stent 10 may be expanded through any conventional
means. For example, the stent 10 in the reduced diameter may be
placed on the balloon tip of a catheter. At the site, the balloon
is expanded to generate radial forces on the interior of the stent
10. The radial forces urge the stent 10 to radially expand without
appreciable longitudinal expansion or contraction. Plastic
deformation of the material of the stent 10 (e.g., stainless steel)
results in the stent 10 retaining the expanded shape following
subsequent deflation of the balloon. Alternatively, the stent 10
may be formed of a super-elastic or shape memory material (such as
nitinol--a well-known stent material which is an alloy of nickel
and titanium).
[0035] As the stent 10 expands, the path lengths 50, 51 straighten
to accommodate the expansion. FIG. 3 illustrates the straightening
of the path lengths 50, 51. In FIG. 3, the stent 10 has been only
partially expanded to an expanded diameter less than a maximum
expanded diameter. At a maximum expanded size, the path lengths 50,
51 are fully straight. Further expansion of the stent 10 beyond the
maximum expanded size would result in narrowing of the minor axis
X.sub.m-X.sub.m (i.e., a narrowing of a separation between the
transverse connection locations and a resulting narrowing of the
length L.sub.r of the stent) or would require stretching and
thinning of the stent material.
[0036] As shown in FIG. 3, during expansion of the stent 10, the
straight segments 16, 18, 20, 22, 24 and 26 are substantially
unchanged. The straightening of the path lengths 50, 51 results in
bending of the arcuate peaks 17, 21, 25 and valleys 19, 23. Since
the width W' of the peaks 17, 21, 25 and valleys 19, 23 is less
than the width W of the straight segments 16, 18, 20, 22, 24 and
26, the arcuate peaks 17, 21, 25 and valleys 19, 23 are less stiff
than the straight segments 16, 18, 20, 22, 24 and 26 and,
therefore, more likely to deform during expansion.
[0037] As the stent 10 expands, the cells 12 assume a diamond shape
shown in FIG. 3. Since the expansion forces are radial, the length
of the major axis X.sub.M-X.sub.M (i.e., the distance between the
longitudinal connection locations 27) increases. The length of the
minor axis X.sub.m-X.sub.m (and hence the length of the stent 10)
remains unchanged.
[0038] The stent 10 is highly flexible. To advance to a site, the
axis X-X of the stent 10 must bend to navigate through a curved
lumen. Further, for placement at a curved site in a lumen, the
stent 10 must be sufficiently flexible to retain a curved shape
following expansion and to bend as the lumen bends over time. The
stent 10, as described above, achieves these objections.
[0039] When bending on its axis X-X, the stent 10 tends to axially
compress on the inside of the bend and axially expand on the
outside of the bend. The present design permits such axial
expansion and contraction. The novel cell geometry 12 results in an
accordion-like structure which is highly flexible before and after
radial expansion. Further, the diamond shape of the cells 12 after
radial expansion resists constricting forces otherwise tending to
collapse the stent 10.
[0040] Numerous modifications are possible. For example the stent
10 may be lined with either an inner or outer sleeve (such as
polyester fabric or ePTFE) for tissue growth. Also, the stent may
be coated with radiopaque coatings such as platinum, gold, tungsten
or tantalum. In addition to materials previously discussed, the
stent may be formed of any one of a wide variety of previous known
materials including, without limitation, MP35N, tantalum, platinum,
gold, Elgiloy and Phynox.
[0041] While three cells 12 are shown in FIG. 2 longitudinally
connected surrounding the circumference C.sub.r of the stent, a
different number could be so connected to vary the properties of
the stent 10 as a designer may elect. Likewise, while each column
of cells 12 in FIG. 2 is shown as having three longitudinally
connected cells 12, the number of longitudinally connected cells 12
could vary to adjust the properties of the stent. Also, while each
longitudinal segment 14 is shown as having three peaks 17, 21, 25
per longitudinal segment 14, the number of peaks could vary. FIG. 7
illustrates a stent 10" with a cell 12" having five peaks 117",
17", 21", 25" and 125" per longitudinal segment 14". Preferably,
the longitudinal segment will have an odd number of peaks so that
the transverse connection points are at an apex of a center
peak.
[0042] FIGS. 8 and 9 illustrate an alternative embodiment where the
major axis X.sub.M'-X.sub.M' of the cells 12' are parallel with the
cylindrical axis X'-X' of the stent 10'. In FIG. 9, the expanded
stent 10' is shown at a near fully expanded state where the path
lengths 50', 51' are substantially linear.
[0043] When forming the stent from shape memory metal such as
nitinol, the stent can be laser cut from a nitinol tube.
Thereafter, the stent can be subjected to a shape-setting process
in which the cut tube is expanded on a mandrel and then heated.
Multiple expansion and heating cycles can be used to shape-set the
stent to the final expanded diameter. Preferably, the final
expanded diameter is equal to the desired deployed diameter of the
stent. During expansion, the stent is preferably axially restrained
such that the length of the stent does not change during expansion.
The finished stent preferably has an austenite finish temperature
less than body temperature. Thus, at body temperature, the stent
will self-expand to the desired deployed diameter due to the shape
memory characteristic of the metal forming the stent.
[0044] In use, the finished stent can be mounted on a delivery
catheter. As is conventionally known in the art, the stent can be
held in a compressed orientation on the delivery catheter by a
retractable sheath. As is also known in the art, the delivery
catheter can be used to advance the stent to a deployment location
(e.g., a constricted region of a vessel). At the deployment cite,
the sheath is retracted thereby releasing the stent. Once released,
the stent self-expands to the deployed diameter.
[0045] It has been noted that the lengths of prior art stents when
mounted on a delivery catheter can be different from the deployed
lengths of such stents. For example, it has been determined that
the deployed lengths of the prior art stents are often shorter than
the compressed orientation lengths (i.e., the lengths of the stents
when mounted on a delivery catheter). Shortening can be problematic
because shortening makes it more difficult for a physician to
accurately place a stent at a desired position in a vessel.
[0046] An important aspect of the present invention relates to a
stent design that reduces or eliminates shortening of a stent. For
example, one embodiment of the present invention relates to a stent
having the same length or substantially the same length at each of
the following stages: 1) when the stent is initially cut from a
tube of shape-memory alloy; 2) when the stent is shape-set to the
desired expanded diameter; 3) when the stent is compressed on the
delivery catheter; and 4) when the stent is deployed at a
deployment location.
[0047] With respect to shape memory stents, it has been found that
varying the width of the segments 16, 18, 20, 22, 24 and 26
controls whether the stent shortens, lengthens, or remains the same
length during expansion from the compressed orientation (i.e., the
reduced diameter orientation) to the deployed orientation. For
example, the segments 26 and 16 are preferably constructed with
enlarged widths adjacent the connection locations 27, and reduced
widths adjacent their corresponding peaks 25 and 17. Similarly, the
segments 22 and 20 are preferably constructed with enlarged widths
adjacent the connection locations 28, and reduced widths adjacent
their corresponding valleys 23 and 19. The relative sizes between
the enlarged widths and the reduced widths controls whether the
stent shortens, lengthens, or remains the same during
expansion.
[0048] FIGS. 10-12 show a stent 210 having a cell structure adapted
to limit any length changes that may occur as the stent is expanded
from the compressed orientation to the deployed orientation.
Preferably the length change between the compressed orientation and
the deployed orientation is less than 5 percent. More preferably,
the length change between the compressed orientation and the
deployed orientation is less than 2 percent. Most preferably, the
stent 210 experiences substantially no length change as it is
released from a delivery catheter and expanded from the compressed
orientation to the deployed orientation.
[0049] FIG. 10 shows the stent 210 cut longitudinally along its
length and laid flat. The stent 210 has a length L and a
circumference C. FIG. 10 is representative of the stent 210 after
the stent 210 has been laser cut from a shape-memory tube, but
before the stent 210 has been shape-set to the expanded diameter.
FIG. 12 shows a portion of the stent 210 after the stent has be
shape-set to the desired expanded diameter. In both FIGS. 10 and
12, the stent 210 is elongated along axis A-A and includes a stent
body (i.e., a three-dimensional structure) having cell defining
portions that define plurality of cells 212. After the stent 210
has been shape-set to the expanded diameter as shown in FIG. 12,
the cells 212 are preferably more open than the cells 212 depicted
in FIG. 10. However, while the circumference C increases, the
length L preferably remains substantially the same at both
diameters.
[0050] Referring to FIG. 11, the cell defining portions of the
stent body include circumferential connection locations 227 and
longitudinal connection locations 228. "Circumferential connection
locations" are locations where circumferentially adjacent cell
defining structures, as defined relative to axis A-A, are connected
together. "Longitudinal connection locations" are locations where
longitudinally adjacent cell defining portions, as define relative
to the axis A-A, are connected together.
[0051] Referring still to FIG. 11, each cell defining portion
includes two axially spaced-apart members 214 (i.e., members that
are spaced-apart from one another along the axis A-A) that extend
circumferentially about the axis A-A in an undulating pattern. The
members 214 extend in the undulating pattern between the
circumferential connection locations 227. Adjacent the
circumferential connection locations 227, the ends of the
undulating members 214 are connected to one another. At the
longitudinal connection locations 228, the undulating members 214
merge with the undulating members 214 of longitudinally adjacent
cell defining portions.
[0052] Still referring to FIG. 11, each undulating member 214 is
shown including: 1) a segment 226 that extends from connection
location 227 to peak 225; 2) a segment 224 that extends from peak
225 to valley 223; 3) a segment 222 that extends from valley 223 to
connection location 228; 4) a segment 220 that extends from
connection location 228 to valley 219; 5) a segment 218 that
extends from valley 219 to peak 217; and 6) a segment 216 that
extends from peak 217 to connection location 227. The segments
216-226 preferably extend generally longitudinally along the stent
210. The term "generally longitudinally" will be understood to mean
that the segments 216-226 are closer to a parallel relationship
relative to the axis A-A of the stent 210 than to a transverse
relationship relative to the axis A-A of the stent 210.
[0053] To prevent length changes during deployment of the stent,
the segments 226 and 216 preferably include enlarged widths W.sub.1
adjacent the connection locations 227, and reduced widths W.sub.2
adjacent their corresponding peaks 225 and 217. Similarly, the
segments 222 and 220 are preferably constructed with enlarged
widths W.sub.1 adjacent the connection locations 228, and reduced
widths W.sub.2 adjacent their corresponding valleys 223 and 219.
Preferably, widths of the segments 226, 222, 220 and 216 taper
(i.e., narrow) continuously along their lengths. As is clear from
FIG. 11, the widths of the segments are measured in a
circumferential direction relative to the axis A-A.
[0054] Referring once again to FIG. 11, pairs of tapered segments
226 and 216 are provided at each circumferential connection
location 227, and pairs of tapered segments 222 and 220 are
provided at each longitudinal connection location 228. Each pair of
tapered segments is defined by an inner cut 250 that is parallel to
the axis A-A of the stent 210, and two outer cuts 252 that are
angled relative to the axis A-A of the stent 210. Preferably, the
outer cuts 252 diverge from one another as the cuts 252 extend
toward their corresponding connection location 227 or 228. The
angled orientation of the cuts 252 causes the segments 224 and 218
which interconnect the pairs of tapered segments 226, 216, 222 and
220 to have a non-tapered configuration. Additionally, the angled
orientation of the cuts 252 causes the segments 224 and 218 to be
angled (i.e., skewed) relative to the axis A-A of the stent
210.
[0055] The narrowing from width W.sub.1 to W.sub.2 results in a
taper along the lengths of the segments 226, 222, 220 and 216.
Preferably, the taper has an angle B in the range of 0.5-5 degrees
relative to the axis A-A of the stent 210. More preferably, the
taper angle B is in the range of 1-3 percent. It has been found
that the relative sizes of W.sub.1 and W.sub.2 have an effect on
the deployed length of the stent 210 (i.e., the length of the stent
after deployment in a vessel) as compared to the compressed length
of the stent 210 (i.e., the length of the stent when mounted on a
delivery catheter). As a result, in the design of the stent, the
widths W.sub.1 and W.sub.2 can be selected to effect a desired
change in length including no change in length if so desired. For
example, a stent having a 5 millimeter cell length L.sub.c (labeled
on FIG. 11), a first width W.sub.1 of 0.0065 inch and a second
width W.sub.2 of 0.0059 inch, has been found to lengthen about 10%
during expansion from the compressed orientation to the deployed
orientation. Alternatively, a stent having a 5 millimeter cell
length L.sub.c (labeled on FIG. 11), a first width W.sub.1 of 0.009
and a second width W.sub.2 of 0.0047, has been found to shorten
about 10% during expansion from the compressed orientation to the
deployed orientation. Further, a stent with a 5 millimeter cell
length L.sub.c (labeled on FIG. 11), a first width W.sub.1 of 0.008
inches, a second width W.sub.2 of 0.0052 inches and an angle B of
two degrees has been found to experience no lengthening and no
shortening when expanded from the compressed orientation and the
deployed orientation.
[0056] While a preferred use for the inventive features disclosed
in FIGS. 10-12 is in a self-expanding stent, the features also have
benefits when used with non-self-expanding stents (e.g., balloon
expandable stents made of a material such as stainless steel).
Also, while FIGS. 10-12 illustrate a preferred geometry for
practicing the present invention, the technique for controlling
length variations by varying the widths of selected portions of a
stent is also applicable to stents having other geometries, shapes,
or strut patterns. Further, the various aspects of the present
invention can also be used to cause a desired shortening or
lengthening of a stent during deployment.
[0057] From the foregoing, the present invention has been shown in
a preferred embodiment. Modifications and equivalents are intended
to be included within the scope of the appended claims.
* * * * *