U.S. patent application number 09/961935 was filed with the patent office on 2002-01-24 for multilayered metal stent.
Invention is credited to Richter, Jacob.
Application Number | 20020010505 09/961935 |
Document ID | / |
Family ID | 25515691 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020010505 |
Kind Code |
A1 |
Richter, Jacob |
January 24, 2002 |
Multilayered metal stent
Abstract
Coated stents for increased radiopacity. In one embodiment, the
present invention includes a stent in the form of a tubular member
comprising struts of a first material, and a first coating on the
tubular member. The first coating substantially covers the tubular
member and is substantially uniform in thickness. The first coating
comprises a second material that is more radiopaque than the first
material. In another embodiment, the stent further comprises a
second coating between the tubular member and the first coating,
wherein the second coating covers only a portion of the tubular
member. In yet another embodiment, the stent is a coated bifurcated
stent for positioning in a bifurcated body lumen.
Inventors: |
Richter, Jacob; (Ramat
Hasharon, IL) |
Correspondence
Address: |
KENYON & KENYON
ONE BROADWAY
NEW YORK
NY
10004
US
|
Family ID: |
25515691 |
Appl. No.: |
09/961935 |
Filed: |
September 24, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09961935 |
Sep 24, 2001 |
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09335599 |
Jun 18, 1999 |
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6315794 |
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09335599 |
Jun 18, 1999 |
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08969576 |
Nov 13, 1997 |
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Current U.S.
Class: |
623/1.15 ;
623/1.34; 623/1.46 |
Current CPC
Class: |
A61F 2002/067 20130101;
A61F 2002/065 20130101; A61F 2250/0098 20130101; A61F 2002/91558
20130101; A61F 2/915 20130101; A61F 2002/91541 20130101; A61F
2230/001 20130101; A61F 2230/0054 20130101; A61F 2/91 20130101 |
Class at
Publication: |
623/1.15 ;
623/1.34; 623/1.46 |
International
Class: |
A61F 002/06 |
Claims
What is claimed is:
1. A stent for deploying within a body lumen, said stent
comprising: a tubular member comprising struts which comprise a
first material, said tubular member having a proximal end and a
distal end and a longitudinal bore therethrough; and a first
coating on said tubular member, said first coating substantially
covering said tubular member and being substantially uniform in
thickness, said first coating comprising a second material; wherein
said second material is more radiopaque than said first
material.
2. The stent of claim 1, wherein the thickness of said first
coating is approximately 1-20 percent of the thickness of an
underlying strut.
3. The stent of claim 2, wherein the thickness of the first coating
is approximately 5-15 percent of the thickness of an underlying
strut.
4. The stent of claim 1, wherein said first coating is
approximately 0.5-20 microns in thickness.
5. The stent of claim 1, wherein said first material is selected
from the group consisting of stainless steel and nitinol.
6. The stent of claim 1, wherein said second material is selected
from the group consisting of gold, platinum, silver and
tantalum.
7. The stent of claim 1, further comprising a second coating
disposed between said tubular member and said first coating, said
second coating covering only a portion of said tubular member.
8. The stent of claim 7, wherein said second coating is located at
said proximal or said distal end of said tubular member.
9. The stent of claim 7, wherein when the stent is observed with
fluoroscopy, said stent appears darker at the portion where said
second coating exists than where said second coating does not
exist.
10. The stent of claim 7, wherein the thickness of said second
coating is approximately 1-20 percent of the thickness of an
underlying strut.
11. The stent of claim 10, wherein the thickness of the second
coating is approximately 5-15 percent of the thickness of an
underlying strut.
12. The stent of claim 7, wherein said second coating is
approximately 0.5-20 microns in thickness.
13. The stent of claim 12, wherein said second coating is
approximately 5-15 microns in thickness.
14. The stent of claim 12, wherein said first coating is
approximately 1 micron in thickness.
15. The stent of claim 7, wherein said second coating comprises a
material selected from the group consisting of gold, platinum,
silver and tantalum.
16. The stent of claim 1, wherein said tubular member is bifurcated
into a trunk leg and a branch leg for positioning in respective
trunk and branch lumens of a bifurcated lumen.
17. The stent of claim 16, further comprising a second coating
between said tubular member and said first coating, said second
coating covering only said branch leg.
18. The stent of claim 16, wherein: said tubular member includes a
branch aperture; said branch leg may be selectively disposed within
said tubular member; and a region of said tubular member adjacent
to said branch aperture includes a second coating between said
tubular member and said first coating.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to stents for deploying within
body lumens, and more particularly, to optimizing the radiopacity
of such stents.
BACKGROUND
[0002] Stents are tubular structures that are implanted inside
bodily conduits, blood vessels or other body lumens to widen and/or
to help keep such lumens open. Typically, stents are delivered into
the body while in a compressed configuration, and are thereafter
expanded to a final diameter once positioned at a target location
within the lumen. Stents are often used following or substituting
for balloon angioplasty to repair stenosis and to prevent future
restenosis and, more generally, may be used in repairing any of a
number of tubular body conduits such as those in the vascular,
biliary, genitourinary, gastrointestinal, respiratory and other
systems. Exemplary patents in the field of stents formed of wire,
for example, include U.S. Pat. Nos. 5,019,090 to Pichuk; 5,161,547
to Tower; 4,950,227 to Savin et al.; 5,314,472 to Fontaine;
4,886,062 and 4,969,458 to Wiktor; and 4,856,516 to Hillstead; each
of which is incorporated herein by reference. Stents formed of cut
stock metal, for example, are described in U.S. Pat. Nos. 4,733,665
to Palmaz; 4,762,128 to Rosenbluth; 5,102,417 to Palmaz and Schatz;
5,195,984 to Schatz; WO 91 FR013820 to Meadox; and WO 96 03092 to
Medinol, each of which is incorporated herein by reference.
Bifurcating stents are described in U.S. Pat. No. 4,994,071 to
MacGregor, and commonly-assigned U.S. Pat. application Ser. No.
08/642,297, filed May 3, 1996, each of which is incorporated herein
by reference.
[0003] For stents to be effective, it is essential that they be
accurately positioned at a target location within a desired body
lumen. This is especially true where, for example, multiple
stenting is required with overlapping stents to cover excessively
long regions or bifurcating vessels. In these and other cases, it
is often necessary to visually observe the stent both during
placement in the body and after expansion of the stent. Various
approaches have been attempted to achieve such visualization. For
example, stents have been made from radiopaque (i.e., not allowing
the passage of x-rays, gamma rays, or other forms of radiant
energy) metals, such as tantalum and platinum, to facilitate
fluoroscopic techniques. One of the potential problems with such
stents, however, is that a useful balance of radiopacity and stent
strength is difficult, if not impossible, to achieve. For example,
in order to form such a stent of adequate strength, it is often
necessary to increase stent dimensions such that the stent becomes
overly radiopaque. Consequently, fluoroscopy of such a stent after
deployment can hide the angiographic details of the vessel in which
it is implanted, thus making it difficult to assess problems such
as tissue prolapse and hyperplasia.
[0004] Another technique that has been used to achieve the
visualization of stents is the joining of radiopaque markers to
stents at predetermined locations. The joining of the stent and
marker materials (e.g., stainless steel and gold, respectively),
however, can create a junction potential or turbulence in blood and
thus promote thrombotic events, such as clotting. Consequently, the
size of the markers is minimized to avoid this problem, with the
adverse effect of greatly decreasing fluoroscopic visibility and
rendering such visibility orientation-sensitive.
[0005] Yet another technique that has been used to achieve the
visualization of stents is to simply increase the thickness of such
stents to thereby increase radiopacity. Overly thick stent struts,
however, effectively create an obstruction to blood flow. In
addition, design limitations for stents having thick struts often
result in large gaps between these struts, thus decreasing the
support of a surrounding lumen. Furthermore, overly thick stent
struts could adversely affect stent flexibility.
[0006] There is thus a need for the increased radiopacity of stents
without sacrificing stent mechanical properties or performance. The
coating of stents with radiopaque materials is described in U.S.
Pat. No. 5,607,442 to Fishell et al. According to this patent, the
disclosed radiopaque coating is much thicker on longitudinal stent
members when compared with radial stent members such that only the
longitudinal stent members are visible during fluoroscopy.
SUMMARY OF THE INVENTION
[0007] The present invention provides stents of optimized
radiopacity and mechanical properties.
[0008] In one embodiment, the present invention includes a stent
comprising a tubular member which comprises struts of a first
material, and a first coating on the tubular member. The first
coating substantially covers the tubular member and is
substantially uniform in thickness. The first coating comprises a
second material that is more radiopaque than the first material
comprising the struts.
[0009] In another embodiment of the present invention, the stent
further comprises a second coating disposed between the tubular
member and the first coating, wherein the second coating covers
only a portion of the tubular member. When the stent is observed
with fluoroscopy, the portion where the second coating exists
appears darker than where only the first coating exists.
[0010] In yet another embodiment of the present invention, the
stent is a coated bifurcated stent for positioning in a body lumen
that is bifurcated into a trunk lumen and a branch lumen. The stent
has trunk and branch legs for positioning in trunk and branch
lumens, respectively. In this embodiment, the stent is coated with
multiple layers of radiopaque materials such when the stent is
observed with fluoroscopy, the branch leg appears darker than the
trunk leg.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1A illustrates a coated patterned stent, in accordance
with an embodiment of the present invention.
[0012] FIG. 1B is a cross-sectional view of a typical strut from
the stent of FIG. 1A.
[0013] FIG. 2A illustrates a preferred stent configuration in an
embodiment of the present invention.
[0014] FIG. 2B illustrates a most preferred configuration for a
single stent cell, in accordance with an embodiment of the present
invention.
[0015] FIG. 3A illustrates a patterned stent having multiple
coatings thereon, in accordance with an embodiment of the present
invention.
[0016] FIG. 3B is a cross-sectional view of a typical strut from
the stent of FIG. 3A, at a location where two coatings have been
applied to the stent.
[0017] FIG. 3C is a cross-sectional view of a typical strut from
the stent of FIG. 3A, at a location where only one coating has been
applied to the stent.
[0018] FIG. 4A illustrates a first coated bifurcated stent, in
accordance with an embodiment of the present invention.
[0019] FIGS. 4B-4C illustrate a second coated bifurcated stent, in
accordance with an embodiment of the present invention.
DETAILED DESCRIPTION
[0020] The present invention provides optimal radiopacity of stents
without sacrificing mechanical properties or performance. A stent
according to the present invention is made from a base material
having desired mechanical properties (e.g., strength) and coated
with a material to provide optimal, radiopacity to the stent. The
radiopacity of the stents of the present invention is optimized in
the sense that, during fluoroscopic procedures, the stents are
entirely visible but are not so radiopaque that angiographic
details are masked. The present invention thus provides for stents
that have both the desired mechanical properties of the base
material and the desired radiopacity of the coating material. The
stents of the present invention have the additional benefit of
being manufactured according to simple and reproducible
techniques.
[0021] In one embodiment of the present invention, stent 100 is a
tubular member 101 comprising struts 110 as shown in FIG. 1A-1B.
The term "strut", as used herein, is intended to mean any
structural member of a stent, such as any radial, longitudinal, or
other members made from wire, cut stock, or other materials. Struts
110 comprise a first material that is selected for its mechanical
properties such as, for example, the ability to be delivered into
the body while in a compressed configuration, the ability to expand
or be expanded once positioned to a target location, the ability to
resist recoil, and the ability to hold open a body lumen during the
stent lifetime. Typical exemplary materials for struts 110 include
stainless steel and nitinol. Stent 100 further comprises a first
coating 102 of a second material that is selected for its
radiopacity. Coating 102 covers the entire tubular member 101 with
the result that intersections of the first and second materials are
not exposed to the exterior of the stent. By not exposing
intersections of the first and second materials to the exterior of
the stent, the risks of creating a junction potential in the blood
and causing the electrolytic corrosion of the stent are precluded.
FIG. 1B shows a cross-sectional view of coating 102 on a typical
strut 110 of stent 100. Although FIG. 1B shows both the strut 110
and coating 102 to be substantially square in cross-sectional
shape, the actual cross-sectional shape of either or both of these
elements is any desired or suitable shape, such as circular,
oval-shaped, rectangular, or any of a number of irregular
shapes.
[0022] Coating 102 is applied to tubular member 101 according to
any suitable technique such as, for example, electroplating,
electroless plating, ion beam aided deposition, physical vapor
deposition, chemical vapor deposition, electron beam evaporation,
hot-dipping or any other suitable sputtering or evaporation
process. Coating 102 comprises any suitable radiopaque material
such as, for example, gold, platinum, silver and tantalum.
[0023] The thickness of coating 102 is an important aspect of the
present invention. A coating that is too thick will result in a
stent that is overly radiopaque, and angiographic details will
consequently be masked during subsequent fluoroscopy. In addition,
stent rigidity often increases with coating thickness, thus making
it difficult to expand the stent for placement in a body lumen if
the coating is too thick. On the other hand, a radiopaque coating
that is too thin will not be adequately visible during fluoroscopy.
Depending on the material and configuration of the tubular member
101; and the material of the coating 102, the thickness of coating
102 is optimized to provide the optimum balance between radiopacity
and strength. In general, however, it is preferred that coating 102
be approximately 1-20%, and more preferably approximately 5-15%, of
the underlying strut thickness. In all embodiments of the present
invention, coating 102 is applied to the entire stent such that it
is wholly visible during fluoroscopy. Accordingly, any suboptimal
expansion at any position along the stent is visible and any
deviations from perfect circular expansion can be noticed.
[0024] The stents of the present invention are of any suitable
configuration, although the patterned configurations as described
in WO 96 03092 and commonly-assigned, allowed U.S. Pat. application
Ser. No. 08/457,354, filed May 31, 1995 and incorporated herein by
reference, are preferred for all embodiments of the present
invention. As an example of such a configuration (a closeup of
which is shown in FIGS. 2A and 2B), stent 100 is a tube having
sides that are formed into a plurality of two orthogonal meander
patterns intertwined with each other. The term "meander pattern" is
used herein to describe a periodic pattern about a center line and
"orthogonal meander patterns" are patterns having center lines that
are orthogonal to each other.
[0025] As shown in FIG. 2A, stent 100 optionally includes two
meander patterns 11 and 12. Meander pattern 11 is a vertical
sinusoid having a vertical center line 9. Meander pattern 11 has
two loops 14 and 16 per period wherein loops 14 open to the right
while loops 16 open to the left. Loops 14 and 16 share common
members 15 and 17, where member 15 connects from one loop 14 to its
following loop 16 and member 17 connects from one loop 16 to its
following loop 14. Meander pattern 12 is a horizontal pattern
having a horizontal center line 13. Meander pattern 12 also has
loops, labeled 18 and 20, which may be oriented in the same or
opposite directions. The stent configuration shown in FIG. 2A, with
orthogonal meander patterns 11 and 12, provides for a high degree
of stent flexibility to facilitate expansion, yet results in a high
degree of rigidity once the stent is expanded. FIG. 2B illustrates
a detailed view of a single cell of the most preferred stent
configuration of the present invention.
[0026] In another embodiment of the invention as shown in FIGS.
3A-3C, stent 200 includes a second coating 202 applied between the
struts 110 of stent 200 and first coating 102. In distinction to
first coating 102, however, second coating 202 covers only a
portion or multiple portions of stent 200 so that isolated regions
of stent 200 are most visible during fluoroscopy. For example,
second coating 202 is applied to one or both of the proximate 111
and distal 112 ends of stent 100, as shown in FIG. 3A. As in the
embodiment shown in FIGS. 1A-1B, however, first coating 102 covers
the entire stent 200 shown in FIGS. 3A-3C. FIGS. 3B and 3C show
cross-sectional views of struts 110 of stent 100 where second
coating 202 has and has not been applied, respectively. Such
isolated marking is useful for the accurate positioning of the ends
of stents, such as, for example, in the case of multiple stenting
wherein the overlapping length is important, or, for example, in
the case of ostial stenting wherein the position of the stent end
relative to the ostium is important.
[0027] Second coating 202 comprises a suitable radiopaque material
such as gold, platinum, silver and tantalum, and may be the same or
different material as first coating 102. Second coating 202 is
applied to stent 200 by any suitable technique, such as those
described for the application of first coating 102. Second coating
202 is applied only to a portion or multiple portions of tubular
member 101, for example, by masking during the application of
second coating 202 or by isolated etching after second coating 202
is applied. It is to be appreciated that although coating 202 is
herein described to be a "second" coating, it is applied to stent
200 before the application of first coating 102.
[0028] When used, second coating 202 has a thickness that will
result in increased radiopacity at the portion(s) where second
coating 202 exists when compared with the portion(s) where second
coating 202 does not exist. Because second coating 202 is applied
to only a portion or multiple portions of stent 200, it can be
thickly applied without significantly affecting the resistance of
stent 200 to expand or affecting the visibility of arterial details
during fluoroscopy. Like first coating 102, the thickness of second
coating 202 is optimized to provide a desired balance between stent
radiopacity and other properties. In general, however, second
coating 202 is typically as thick or thicker than first coating
102. When both first and second coatings 102, 202 are applied, it
is generally preferred that the thickness of first and second
coatings 102, 202 are about 1-5% and 5-15%, respectively, of the
underlying stent strut thickness. Furthermore, the combined
thickness of first and second coatings 102, 202 typically does not
exceed 25% of the underlying stent strut thickness. As an
illustrative example, second coating 202 is applied to a thickness
of about 10 microns onto a stent having 100 micron diameter struts.
First coating 102 is then applied to a thickness of about 1
micron.
[0029] In another embodiment of the present invention, stent 300 is
a bifurcated stent as shown in FIG. 4A. Stent 300 comprises a
tubular member 301 that is bifurcated into tubular trunk and branch
legs 310, 311 for positioning in trunk and branch lumens of a
bifurcated lumen, respectively. In this embodiment, the entire
stent is coated with first coating 102 as described for the
embodiments shown in FIGS. 1 and 3. Branch leg 311, however,
includes second coating 202 disposed between tubular member 301 and
first coating 102 such that when stent 300 is observed with
fluoroscopy, branch leg 311 appears darker than the trunk leg 310.
The cross-sectional views of the struts of stent 300 thus appear as
shown in FIGS. 3B and 3C for branch and trunk legs 311, 310,
respectively. Such a configuration is useful for aligning and
inserting branch leg 311 into a branch lumen.
[0030] Alternatively, branch leg 311 may be selectively inserted
into branch aperture 312 of tubular member 301 so that tubular
member 301 and trunk leg 310 are separately delivered into a
bifurcated lumen. In this case, tubular member 301 is provided with
a branch aperture 312 as shown in FIG. 4B. When tubular member 301
is delivered to a bifurcated lumen, branch aperture 312 is aligned
with the corresponding branch lumen. Tubular member portion 301 of
stent 300 is thereafter expanded to secure its position in the
lumen to be treated, and branch leg 311 is delivered through branch
aperture 312 so that part of branch leg 311 is positioned into the
branch lumen. Branch leg 311 is thereafter expanded as shown in
FIG. 4C in an amount sufficient for its external surface to engage
the portion of the tubular member 301 defining the branch aperture
312 and secure the branch leg 311 in the branch lumen and tubular
member portion 301. In this embodiment of the invention, a region
313 surrounding branch aperture 312 includes both first and second
coatings 102, 202 such that region 313 is most visible during
fluoroscopy. In other words, the cross-sectional view of the struts
110 of stent 300 appear as shown in FIG. 3B for region 313, and as
shown in FIG. 3C elsewhere. Such a configuration is useful for
aligning branch aperture 312 with a branch lumen so that branch leg
310 is thereafter easily inserted into the branch lumen.
[0031] The present invention provides stents having optimal
radiopacity without sacrificing stent properties or performance.
Those with skill in the art may recognize various modifications to
the embodiments of the invention described and illustrated herein.
Such modifications are meant to be covered by the spirit and scope
of the appended claims.
* * * * *