U.S. patent application number 10/263000 was filed with the patent office on 2003-02-06 for stent-graft assembly with thin-walled graft component and method of manufacture.
Invention is credited to Birdsall, Matthew J., Lashinski, Robert D., Nolting, John E., Shull, Samuel L., Williams, Michael S..
Application Number | 20030028240 10/263000 |
Document ID | / |
Family ID | 21982225 |
Filed Date | 2003-02-06 |
United States Patent
Application |
20030028240 |
Kind Code |
A1 |
Nolting, John E. ; et
al. |
February 6, 2003 |
Stent-graft assembly with thin-walled graft component and method of
manufacture
Abstract
A stent-graft assembly having a thin-walled membrane and method
of preparing the same are disclosed. In a first embodiment, the
assembly comprises a stent, a coating and a porous membrane,
wherein the membrane is less than 0.040 inch thick or less.
Portions of the coating extend into the pores of the thin membrane
to sealingly engage the membrane to achieve secure adhesion. In a
second embodiment the coating and thin membrane bond to form a
homogenous structure. In an alternative embodiment, the assembly
comprises an inner and outer thin membrane bound to one another
through the interstices of the support member and a coating at the
proximal and distal regions. In any of the foregoing embodiments,
the proximal and distal regions of the stent-graft assembly may
comprise an additional coating, whereby layers of material are
sealed, thereby minimizing thrombogenic potential of free ends of
the assembly.
Inventors: |
Nolting, John E.; (Santa
Rosa, CA) ; Williams, Michael S.; (Santa Rosa,
CA) ; Birdsall, Matthew J.; (Santa Rosa, CA) ;
Lashinski, Robert D.; (Sebastopol, CA) ; Shull,
Samuel L.; (Santa Rosa, CA) |
Correspondence
Address: |
MEDTRONIC AVE, INC.
3576 UNOCAL PLACE
SANTA ROSA
CA
95403
US
|
Family ID: |
21982225 |
Appl. No.: |
10/263000 |
Filed: |
October 1, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10263000 |
Oct 1, 2002 |
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09053145 |
Mar 31, 1998 |
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6488701 |
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Current U.S.
Class: |
623/1.13 ;
427/2.25; 623/901 |
Current CPC
Class: |
A61F 2250/0023 20130101;
B29C 53/60 20130101; A61F 2/07 20130101; B29C 53/38 20130101; A61F
2/91 20130101; B29L 2023/007 20130101; A61F 2/90 20130101; A61F
2250/0039 20130101; A61F 2002/072 20130101 |
Class at
Publication: |
623/1.13 ;
623/901; 427/2.25 |
International
Class: |
A61F 002/06 |
Claims
We claim:
1. A stent-graft assembly comprising: a generally cylindrical stent
comprising at least one support member, an exterior and an
interior, a medial region, a proximal region and a distal region,
said at least one support member defining a passageway through the
stent; at least one membrane, said at least one membrane affixed to
at least a portion of at least one of said interior and exterior,
wherein the at least one membrane defines at least one of a luminal
surface and a vascular surface, said at least one membrane being
less than 0.040 inch thick.
2. The stent-graft assembly according to claim 1 wherein the
membrane is less than 0.0016 inch thick.
3. The stent-graft assembly according to claim 1 wherein the at
least one membrane is of generally uniform thickness.
4. The stent-graft assembly according to claim 1 wherein the stent
further comprises: a first polymeric coating substantially
encapsulating at least a portion of the at least one support
member; and the at least one membrane is affixed to the
coating.
5. The stent-graft assembly according to claim 4 wherein the at
least one membrane is porous and the coating extends into the pores
of the membrane.
6. A stent-graft assembly according to claim 4 wherein the at least
one membrane and the coating are homogeneously bound to one
another.
7. The stent-graft assembly according to claim 1 wherein the stent
comprises at least one interstice, and the at least one membrane
comprises a first inner membrane defining a luminal surface and a
second outer membrane defining a vascular surface, wherein the
first and second membranes are bound together through the at least
one interstice.
8. The stent-graft assembly according to claim 7 wherein the at
first one membrane is sintered to the second membrane.
9. The stent-graft assembly according to claim 1 wherein the
assembly also comprises a coating at the proximal and distal
regions of the assembly.
10. The stent-graft assembly according to claim 9 wherein the
coating substantially encapsulates the exterior and the interior of
the at least one membrane at the proximal and distal regions of the
assembly.
11. The stent-graft assembly of claim 4 wherein the assembly also
comprises a second coating at the proximal and distal regions of
the assembly.
12. The stent-graft assembly of claim 11 wherein the second coating
substantially encapsulates the exterior and the interior or the at
least one membrane at the proximal and distal regions of the
assembly.
13. The stent-graft assembly of claim 1 wherein said at least one
membrane is a polymer selected from the group consisting of
polyurethane, polytetrafluoroethylene, dimethyl terephthalate,
polyester, polyethylene terephthalate and silicone.
14. The stent-graft assembly of claim 4 wherein the coating is a
polymer selected from the group consisting of polyurethane,
flourinated ethylene propylene and silicone.
15. The stent graft assembly of claim 1 wherein the at least one
support member comprises: at least one stent element formed of a
plurality of substantially straight segments and configured to
provide a plurality of upper and lower peaks; and the at least one
stent element being capable of retaining a compressed configuration
while mounted onto an outer surface of a catheter for delivery to
an affected area of a vessel until application of an outward radial
force to form an expanded configuration.
16. The stent-graft assembly of claim 1 wherein the membrane
comprises a primary diameter and wherein the membrane is
distensible over a range of between 7 and 100% beyond the primary
diameter.
17. A method of forming a stent-graft assembly, the method
comprising the steps of: preparing at least one tube by first
providing a polymeric tape of less than 0.010 inch thickness;
winding the polymeric tape helically around at least a portion of
the length of the mandrel; placing the wrapped mandrel in an oven
at a sufficient temperature and for a sufficient time to achieve
sintering of the tape; providing a generally cylindrical stent
having an interior and an exterior, first and second ends and at
least one support member; coating at least a portion of the at
least one support member with a coating to substantially
encapsulate at least a portion of the at least one support member;
placing the at least one tube contiguous with at least a portion of
the interior or the exterior of the stent to define at least one of
a luminal surface or a vascular surface; and introducing a solvent
in order to bond the at least one tube to the coating.
18. The method of claim 17 wherein the step of coating the stent
comprises: mounting an end of the stent on a rotating mandrel;
heating the stent; spraying the rotating stent with polymer in
solution; curing the stent; alternating the end of the stent that
is mounted on the mandrel; repeating the foregoing steps.
19. The method of claim 17 wherein the step of coating the stent
comprises a vapor deposition process.
20. The method of claim 17 wherein the step of coating the stent
comprises dipping the stent into a polymeric solution.
21. The method of claim 17 wherein the coating is a polymer
selected from the group consisting of polyurethane, silicone and
flourinated ethylene propylene.
22. The method of claim 17 wherein the tape comprises a polymer
selected from the group consisting of ePTFE, polyurethane, dimethyl
terephthalate, polyester, polyethylene terephthalate and
silicone.
23. The method of claim 17 wherein the stent-graft assembly also
comprises a proximal region and a distal region, with the
additional step of coating the proximal and distal regions of the
stent-graft assembly.
24. The method according to claim 17 wherein the tape comprises a
width and a plurality of edges, wherein the tape is wound around
the mandrel such that adjacent edges of tape overlap 10-60 per cent
of the width of the tape.
25. The method according to claim 17 wherein the tape is wound
about the mandrel at an angle to the longitudinal axis of the
mandrel, wherein the angle is between 30 and 60 degrees.
26. The method according to claim 17 wherein the wrapped mandrel is
heated in an oven for between 30 and 45 minutes.
27. The method according to claim 17 wherein the step of
introducing a solvent comprises placing the assembly within a
super-saturated atmosphere of solvent.
28. A method for preparing a stent-graft assembly, the method
comprising the steps of: providing a polymeric tape of less than
0.010 inch thickness; helically winding the tape about a mandrel;
heating the wrapped mandrel at sufficient temperature for
sufficient time to achieve sintering of the tape to prepare a first
thin-walled polymeric tube; removing the tube from the mandrel;
repeating the foregoing steps to prepare a second thin-walled
polymeric tube; providing a generally cylindrical stent having an
interior and an exterior, a proximal region and a distal region, at
least one interstice and at least one support member; lining at
least a portion of the interior of the stent with the first tube to
define a luminal surface; placing the second tube over at least a
portion of the exterior of the stent to define a vascular surface;
and bonding the first and second tubes to one another through the
at least one interstice of the stent.
29. The method according to claim 28 with the added step of dipping
the proximal and distal regions of the assembly into a polymeric
solution.
30. The method according to claim 28 wherein the step of bonding
the first tube to the second tube comprises heating the assembly
for sufficient time at sufficient temperature to achieve sintering
of the tubes to one another through the at least one
interstice.
31. A method for preparing a thin-walled graft tube, the method
comprising the steps of: providing a polymeric tape of less than
0.010 inch thickness; helically winding the tape about a mandrel;
applying pressure to the wrapped mandrel; and heating the wrapped
mandrel under pressure at a sufficient temperature for a sufficient
time to achieve sintering of the tape.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to endoluminal
grafts for stenotic or diseased lumens and methods of making such
grafts. More particularly, the invention includes a stent-graft
assembly comprising a thin-walled graft component and methods of
making the assembly.
BACKGROUND OF THE INVENTION
[0002] A wide range of medical treatments have been previously
developed using "endoluminal prostheses," which terms are herein
intended to mean medical devices which are adapted for temporary or
permanent implantation within a body lumen, including both
naturally occurring or artificially made lumens. Examples of lumens
in which endoluminal prostheses may be implanted include, without
limitation: arteries, such as those located within the coronary,
mesentery, peripheral, or cerebral vasculature; veins;
gastrointestinal tract; biliary tract; urethra; trachea; hepatic
shunts; and fallopian tubes. Various types of endoluminal
prostheses have also been developed, each providing a uniquely
beneficial structure to modify the mechanics of the targeted
luminal wall.
[0003] For example, various grafts, stents, and combination
stent-graft prostheses have been previously disclosed for
implantation within body lumens. More specifically regarding
stents, various designs of these prostheses have been previously
disclosed for providing artificial radial support to the wall
tissue which forms the various lumens within the body, and often
more specifically within the blood vessels of the body. An example
of such a stent displaying optimal radial strength includes, but is
not limited to, the stent disclosed in U.S. Pat. No. 5,292,331 to
Boneau, the disclosure of which is herein incorporated by
reference. Stents of other designs are known in the art, and may
also be suitable for use in the stent-graft assembly. Other example
of stents include but are not limited to those disclosed in U.S.
Pat. No. 4,733,665 issued to Palmaz, U.S. Pat. No. 5,195,984 issued
to Schatz, or U.S. Pat. No. 5,514,154 issued to Lau. Stents are
used alone or in conjunction with grafts.
[0004] The use of an angioplasty balloon catheter is common in the
art as a minimally invasive treatment to enlarge a stenotic or
diseased blood vessel. This treatment is known as percutaneous
transluminal angioplasty, or PTA. To provide radial support to the
treated vessel in order to prolong the positive effects of PTA, a
stent may be implanted in conjunction with the procedure. Under
this procedure, the stent may be collapsed to an insertion diameter
and inserted into a body lumen at a site remote from the diseased
vessel. The stent may then be delivered to the desired site of
treatment within the affected lumen and deployed to its desired
diameter for treatment. Although the stents listed above are
balloon expandable, stents which rely on other modes of deployment
such as self-expansion, may be used to make a device according to
the present invention. Because the procedure requires insertion of
the stent at a site remote from the site of treatment, the device
must be guided through the potentially tortuous conduit of the body
lumen to the treatment site. Therefore, the stent must be capable
of being reduced to a small insertion diameter and must be
flexible.
[0005] During an angioplasty procedure, atheromatous plaques
undergo fissuring, thereby creating a thrombogenic environment in
the lumen. Excessive scarring may also occur following the
procedure, potentially resulting in reocclusion of the treated
lumen. Attempts to address these problems include providing a
suitable surface within the lumen for more controlled healing to
occur in addition to the support provided by a stent. These
attempts include providing a lining or covering in conjunction with
an implanted stent. A stent with such a lining or covering is known
in the art as a stent-graft.
[0006] The graft component, or membrane, of a stent-graft may
prevent excessive tissue prolapse or protrusion of tissue growth
through the interstices of the stent while allowing limited tissue
in-growth to occur to enhance the implantation. The surface of the
graft material at the same time may minimize thrombosis, prevent
scarring from occluding the lumen, prevent embolic events and
minimize the contact between the fissured plaque and the
hematological elements in the bloodstream.
[0007] A combination stent-graft may serve other objectives, such
as delivering therapeutic agents via the assembly, excluding
aneurysms or other malformations, occluding a side branch of a
lumen without sacrificing perforator branches, conferring
radiopacity on the device, and others. Various designs to achieve
these objectives include stents partially or completely coated or
covered with materials, some of which are impregnated with
therapeutic agents, radiopaque elements, or other features designed
to achieve the particular objectives of the device.
[0008] A graft component may be combined with a stent in order to
achieve some or all of the foregoing objectives. However, adding a
graft layer to the stent increases the challenges of delivering a
stent via a catheter by increasing the crossing profile, or
diameter, of the device, and by decreasing the flexibility of the
device. Because the angioplasty process requires the insertion of
the device into a body lumen at a site remote from the site of
treatment and the guiding of the device the body lumen to the
treatment site, it is required that the device be both capable of
being collapsed to a relatively small diameter and be quite
flexible. Moreover, flexibility and a desirable insertion diameter
must be achieved without sacrificing the treatment objectives of
the assembly, which include, at a minimum, radial strength.
Therefore, an objective of a combination stent and graft is
achieving the advantages of both a stent and a graft without
significantly increasing the crossing profile of the device or
significantly decreasing the flexibility of the device.
[0009] Various methods of manufacturing graft devices alone have
been disclosed in the art. One such method for manufacturing a
graft is disclosed in U.S. Pat. No. 5,641,373, issued to Shannon et
al. The disclosed method comprises reinforcing an extruded
flouropolymer tube with a second flouropolymer tube. The second
tube is prepared by winding fluoropolymer tape around the exterior
of a mandrel and heating it to form a tube. The graft may then be
mounted on an anchoring mechanism such as a stent or other fixation
device.
[0010] Another example of a graft is disclosed in U.S. Pat. No.
4,731,073, issued to Robinson. The graft disclosed therein
comprises multiple layers of segmented polyether-polyurethane which
form multiple zones having varying porosities.
[0011] U.S. Pat. No. 5,628,786, issued to Banas, discloses a
polytetrafluoroethylene (PTFE) graft which has a reinforcing
structure integrally bound to the graft. The reinforcing structure
may be in the form of a rib which is sintered or otherwise
integrally bound to the graft.
[0012] U.S. Pat. No. 5,207,960, issued to Moret de Rocheprise,
discloses a process for the manufacture of a thin-walled tube of
fluorinated resin tape. The method includes winding the tape around
a mandrel and sintering the tape. While still on the mandrel, the
tube is rolled to elongate the tube, to reduce the thickness of the
tube, and to facilitate removal of the tube from the mandrel. The
patent discloses that the tubes obtained can be used particularly
as sheaths for the lining of metal tubes.
[0013] There are also numerous examples of combination stent-grafts
disclosed in the art. U.S. Pat. No. 5,653,747 issued to Dereume
discloses a stent to which a graft is attached. The graft component
is produced by extruding polymer in solution into fibers from a
spinnerette onto a rotating mandrel. A stent may be placed over the
fibers while on the mandrel and then an additional layer of fibers
spun onto the stent. The layer or layers of fibers may be bonded to
the stent and/or one another by heat or by adhesives.
[0014] PCT Application WO 95/05132 discloses a stent around which a
thin film of PTFE has been wrapped circumferentially one time and
overlapped upon itself to form a seam. The stent may be
alternatively or additionally placed to cover the interior of the
stent. Fluorinated ethylene propylene is used as an adhesive to
affix the graft to the stent.
[0015] A specific example of a coated stent is disclosed by Pinchuk
in European Patent Application EP 0 797 963 A2. The objectives of
Pinchuk's invention include both increasing the hoop strength and
decreasing the thrombogenic potential of a criss-crossed wire stent
or a zig-zag stent. Pinchuk's application also discloses covering
the coated stent in the manner disclosed in U.S. patent application
No. 5,653,747 issued to Dereume, discussed above.
[0016] An example of a stent and tubular graft is disclosed in U.S.
Pat. No. 5,522,882 issued to Gaterud, et al. Gaterud discloses an
expandable stent mounted on a balloon and a graft mounted over the
stent.
[0017] U.S. Pat. No. 5,123,917 issued to Lee discusses a flexible
and expandable inner tube upon which separate ring scaffold members
are mounted, and a flexible and expandable outer tube enclosing the
inner tube and scaffold members. The rings may be secured to the
inner liner with an adhesive layer. Alternatively, the liners may
be adhered to each other with the rings trapped between the layers.
Lee discloses that the luminal surface of the device may be coated
with various pharmacological agents.
[0018] Similarly, U.S. Pat. Nos. 5,282,823 and 5,443,496, both
issued to Schwartz, et al. disclose a stent with a polymeric film
extending between the stent elements, and strain relief means in
the form of cuts in the film to allow the stent to fully expand and
conform to the interior of the lumen. The thin polymeric film is
applied to the stent while in solution and dried. Once dried, cuts
are made in the film to provide strain relief means.
[0019] Another assembly includes a stent embedded in a plastic
sleeve or stitched or glued to a nylon sleeve, as in U.S. Pat. No.
5,507,771, issued to Gianturco. Other prior art devices requiring
stitching of the graft to the stent are disclosed in European
Patent Application EP 0 686 379 A2, which teaches a perforate
tubular frame having a fabric liner stitched to the frame, and
World Intellectual Property Organization Application Number WO
96/21404 which indicates that the graft be stitched to the stent,
and possibly to loops or eyelets which are part of the stent
structure.
[0020] U.S. Pat. No. 5,637,113 issued to Tartaglia teaches a stent
with a sheet of polymeric film wrapped around the exterior.
Tartaglia teaches that the film is attached to the stent at one end
by an adhesive, by a hook and notch arrangement, or by dry heat
sealing. The polymer can also be attached to the stent by wrapping
the film circumferentially around the stent and attaching the
polymer film to itself to form a sleeve around the stent by heating
and melting the film to itself, adhesive bonding, solvent bonding,
or by mechanical fastening, such as by a clip. The film may be
loaded or coated with a therapeutic agent.
[0021] U.S. Pat. No. 5,628,788, issued to Pinchuk, discloses a
process of melt-attaching a graft to a stent by disposing a layer
of material between the stent and graft which has a lower melting
point than the graft, and heating the assembly to the melting point
of the low-melting point material. Pinchuk also teaches adhering a
textile graft to a stent by coating a stent with vulcanizing
silicone rubber adhesive and curing the adhesive. Pinchuk discloses
a similar stent-graft assembly in European Patent Application EP 0
689 805 A2 and teaches that the graft member can be bonded to the
stent member thermally or by the use of adhesive agents.
[0022] Similarly, World Intellectual Property Organization
Application No. WO 95/05132 discloses a stent with and inner and/or
an outer liner wrapped around the stent to form a seam, with the
liner(s) affixed using an adhesive or melt-attached using a layer
of a material with a lower melting point.
[0023] U.S. Pat. No. 5,645,559, issued to Hachtman, et al.,
discloses a multiple layer stent-graft assembly comprising a first
layer defining a hollow tubular construction, a second layer having
a self-expanding braided mesh construction and a layer of polymeric
material disposed between the first and second layers. The
polymeric material may be adhered by two-sided adhesive tape. The
self-expanding braided mesh, the tubular material, or both may be
larger in diameter in the distal regions than in the medial
region.
[0024] U.S. Pat. No. 5,534,287, issued to Lukic, discloses methods
which result in a covered stent, the covering adhered via a lifting
medium.
[0025] U.S. Pat. No. 5,674,241, issued to Bley, et al. teaches that
a hydrophilic polymer layer may be laminated, embedded, coated,
extruded, incorporated, or molded around an expandable mesh stent
while the stent is in its collapsed condition, and the stent and
graft permitted to expand upon hydration.
[0026] European Patent Application No. EP 0 775 472 A2 discloses a
PTFE-covered stent. The stent can be covered by diagonally winding
an expanded PTFE tape under tension around an at least partially
expanded stent.
[0027] Challenges arising in the art which none of the prior art
adequately addresses include achieving a stent-graft assembly of
sufficiently small crossing profile and which is sufficiently
flexible. Other challenges include minimizing, if not eliminating,
migration of the stent, graft or stent-graft; minimizing, if not
eliminating, delamination of the stent and graft material; and
minimizing thrombogenic potential, vessel reocclusion and tissue
prolapse following deployment. Shortcomings associated with the
prior art include: assemblies with undesirably large crossing
profiles; assemblies with insufficient flexibility; inadequate
adhering of coatings and coverings to stents; inadequate adhering
of coatings to coverings; failure to shield the injured vascular
surface; failure to prevent tissue ingrowth from occluding the
lumen; failure to minimize the embolization of particles loosely
adherent to the vessel wall (especially during device placement and
deployment); and increased thrombogenic potential arising from
delamination of the stent and graft material.
SUMMARY OF THE INVENTION
[0028] The present invention and its varied embodiments address
several problems associated with the prior art. It is a first
objective of this invention to provide an improved stent-graft
assembly for the repair and support of a body lumen. It is a second
objective of this invention to provide an improved stent-graft
assembly with ample radial strength and minimal thrombogenic
potential without appreciably increasing the profile of the device
over that of the stent alone. Further, the decreased profile
following deployment may reduce the thrombogenic potential of the
device. It is a further objective of this invention to provide a
thin-walled stent-graft with both ample radial strength and ample
flexibility.
[0029] It is a further objective of this invention to solve the
problem in the prior art of inadequate adhesion between the stent
and graft material.
[0030] An additional objective of this invention is to balance the
need for some tissue in-growth against the need to minimize
thrombogenic potential and excessive cell growth through the
interstices of the stent. This objective is achieved by providing a
non-thrombogenic, thin-walled stent-graft assembly which is a
smoother device, especially in regions where the prior art
stent-graft has a tendency to fray, delaminate, or exhibit a
scissoring effect. This objective is also achieved by providing a
thin-walled stent-graft assembly which shields the injured vascular
surface, controls excessive tissue in-growth through the stent, and
minimizes the embolization of particles loosely adherent to the
vessel wall especially during placement and deployment of the
device. The device can also be used to control the luminal
protrusion of dissection planes created during PTA or spontaneous
fissuring.
[0031] A stent-graft assembly according to the present invention
first comprises a generally cylindrical stent which comprises at
least one support member. Some or all of the support member or
members comprise a coating which substantially encapsulates the
coated support member or members. Further, the stent-graft includes
an ultra-thin membrane or covering which is attached to the
coating.
[0032] In one embodiment, the proximal and distal regions of the
stent-graft have an additional coating over the first coating and
the membrane. In an alternative embodiment, the proximal and distal
regions of the stent may be left completely uncoated and uncovered
if needed for the particular medical application of the device.
[0033] The thin membrane may be either on the inner or the outer
surface of the stent or both. The material used for the membrane
comprises an ultra-thin polymer. In use, the membrane may have
varying degrees of distensibility depending upon the desired
application of the device. The membrane is bound to the coating
either as a result of defining a homogeneous material with the
coating or as a result of extensions of the coating into the pores
of the membrane and the resulting interlocking engagement between
the coating extensions and the pores of the membrane to form a
composite. An alternative embodiment of the invention comprises a
stent with either a continuous membrane or more than one membrane
on the interior and on the exterior of the stent, the membranes
bound to one another through the interstices of the stent. The
membrane(s) may be sintered or otherwise bound to itself or to one
another. The invention also contemplates the use of a coating at
the proximal and distal regions of the stent, which substantially
encapsulates the assembly at the proximal and distal regions.
[0034] The method according to a first embodiment of the present
invention comprises helically wrapping ultra-thin polymeric tape
around a mandrel, adjusting the angle of orientation of the tape to
the mandrel depending upon the desired distensibility of the
membrane and allowing adjacent edges of the helical wrapping to
overlap somewhat; sintering the tape to itself over the mandrel to
produce a thin tube; removing the thin tube from the mandrel;
coating a stent with a polymer; covering and/or lining the coated
stent with the thin tube; introducing a solvent to attach the
coating to the membrane; curing the assembly to drive off remaining
solvent.
[0035] The method according to an alternative embodiment comprises
winding the polymeric tape around the mandrel to form two layers,
in each layer reversing the angle of orientation of the tape to the
longitudinal axis of the mandrel to form a bias ply, and then
following the remaining steps of the method described above. In any
given embodiment, the angle of orientation of the tape to the
longitudinal axis of the mandrel, dependent on the width of tape
and diameter of the mandrel, can be varied depending upon the
desired distensibility of the graft component of the device. The
sintering parameters can also be varied to affect the
distensibility of the device. Further, pressure may be utilized in
conjunction with sintering to improve the adherence of the tape.
And finally, the amount of overlap between adjacent edges of tape
can be varied depending upon the particular indication for the
device.
[0036] In yet a further embodiment of a method according to the
invention, a thin-walled stent-graft assembly, having inner and
outer membranes, can be fabricated utilizing pressure and heat.
[0037] In any of the methods according to the particular
embodiment, the extent that the coating and membrane cover the
stent can be varied. And the manner in which the membrane is
wrapped about the mandrel, specifically, helically or otherwise.
Also according to the particular embodiment, the proximal and
distal regions of the stent-graft assembly may be coated a second
or multiple times to seal the resulting layers of stent, coating
and membrane, and to substantially increase bond strength due to
the increased surface area of the encapsulation of the stent
strut.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 illustrates a perspective view of a suitable stent
for use in the present invention.
[0039] FIG. 2 illustrates a perspective view with a progressive
partial cut-away of an embodiment of the stent-graft assembly
according to the present invention.
[0040] FIGS. 3A-3C illustrate a portion of the method of
preparation of the membrane component of an embodiment of the
stent-graft assembly according to the present invention.
[0041] FIGS. 4A and 4B illustrate a cross-sectional view of an
embodiment of the invention taken along line A-A of FIG. 2.
[0042] FIGS. 5A-5D respectively illustrate the sequential results
of the steps of a method according to one embodiment of the present
invention.
[0043] FIGS. 6A and 6B show a cross-sectional view of the device
taken along line A-A of FIG. 2 of an alternate embodiment of the
present invention.
[0044] FIGS. 7A-7D respectively illustrate the sequential results
of the steps of a method according to one embodiment of the present
invention.
[0045] FIG. 8 illustrates a perspective view of a partial
progressive cut-away of an alternative embodiment of the
invention.
[0046] FIG. 9 illustrates a perspective view of a partial
progressive cut-away of yet another embodiment of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0047] The thin-walled stent-graft assembly according to the
present invention is shown in FIG. 2. One recommended stent for use
as the stent member according to the present invention is shown at
stent (9) in FIG. 1. Other stents, such as those disclosed in U.S.
Pat. No. 4,733,665 issued to Palmaz, U.S. Pat. No. 5,195,984 issued
to Schatz, or U.S. Pat. No. 5,514,154 issued to Lau may also be
suitable for use in the stent graft assembly.
[0048] Stent (9) is shown in FIG. 1 to include a series of
connected, individual sinusoidal-shaped stent elements (10). Each
individual element is similar in design and construction to the
endovascular support device disclosed in U.S. Pat. No. 5,292,331
issued to Boneau, the disclosure of which is herein incorporated by
reference thereto. For the purpose of further illustration,
however, the series of adjacent rings or circumferential wires form
support members, such as is shown for the purpose of illustration
at support member (11). Each ring is formed to include a serpentine
shape which includes a plurality of peaks and struts extending
longitudinally between adjacent peaks, such as is shown for example
at strut (12) which extends between peaks (13,14). Each ring is
further connected to an adjacent ring in at least one location
where the peaks of their serpentine shape meet, resulting in an
interconnected series of stent elements which forms generally
cylindrical body (15). Cylindrical body (15) further forms a
prosthesis passageway (16) extending through the plurality of
adjacent, serpentine-shaped rings along longitudinal axis L and
between proximal prosthesis port (17) and distal prosthesis port
(18).
[0049] Further to the interconnected series of stent elements and
their respective wire-like support members which form cylindrical
body (15) as shown in FIG. 1, spaces remain along cylindrical body
(15) between adjacent peaks of each shaped ring and also between
adjacent rings, particularly where the individual peaks of adjacent
rings extend away from each other relative to longitudinal axis
L.
[0050] Turning now to FIG. 2, a stent-graft assembly according to
one embodiment of the present invention comprises a stent (9)
having a coating (20) on some or all of the support members (11).
The stent-graft assembly further comprises a thin membrane (21)
which in this embodiment defines a vascular surface (22), but which
in alternate embodiments may form a luminal surface or both a
vascular and luminal surface. The membrane is less than 0.040 inch
in thickness, and preferably is 0.00016 inch thick or less, and is
distensible over a range of between 7 and 100 per cent over its
primary unstretched diameter. Suitable material for the membrane
may be synthetic and is preferably expanded polytetrafluoroethylene
(ePTFE), but may include but is not limited to polyesters,
polyurethane and silicone.
[0051] The proximal and distal regions may comprise a second
coating (34), as illustrated on the distal region only in FIG. 2.
Suitable material for the coating includes but is not limited to
polyurethane, fluorinated ethylene propylene, and silicone. A
therapeutic agent or radiopaque marker may be incorporated into the
second coating or the membrane using a number of different
techniques known in the art, including loading, coating or
laminating.
[0052] A portion of the method of preparation of the thin-walled
graft component is illustrated in FIGS. 3A and 3B. Successive
helical windings (70) of the thin polymeric tape (0.010 inches in
thickness or less)(72) overlap to a desired extent. The amount of
overlap can be varied depending upon the width of the tape,
diameter of mandrel and the angle of the tape to the longitudinal
axis of the mandrel. The invention contemplates that the adjacent
edges of the tape overlap between 5 and 90 per cent of the width of
the tape, with 10 to 60 per cent preferred. The finished graft
component is distensible over a varying range depending upon the
angle .alpha. of the tape to the longitudinal axis of the mandrel
L. The lesser the angle .alpha., the greater the radial
distensibility. The degree of distensibility is also affected by
the sintering process, and the parameters followed to achieve
sintering of the tape may be varied depending upon the desired
radial distensibility. The tape can be wound at any desired angle
.alpha. to the longitudinal axis of the mandrel, more specifically,
.alpha..ltoreq.90.degree.. But in this embodiment the angle is
preferably between 30 and 60 degrees. The tape is wound beginning
from one end of the mandrel progressively to the other end of the
mandrel. It can then be wound a second time in the reverse
direction if an additional layer of polymeric tape is desired, such
as shown in FIG. 3C.
[0053] The wrapped mandrel is then subject to a sufficient
temperature for a sufficient time to sinter the overlap layers
together. For example, a PTFE wrapped mandrel is subject to a
temperature of approximately 370 degrees C. for between 30 and 45
minutes to sinter the overlapping portions together. Pressure may
be utilized in conjunction with sintering to improve the adherence
of the tape windings to one another.
[0054] An alternative sintering method for forming the thin-walled
tube utilizes a radial compression process such as, hot isostatic
compression. A preferred embodiment of which comprises placing the
wrapped mandrel into a vial which is packed in a media such as,
silica or other microbeads. A plunger is placed and held within the
vial under pressure. The vial containing the wrapped mandrel under
pressure is then heated at sufficient time and temperature to
achieve sintering. As illustrated in FIG. 3B, after sintering, the
ends (74) of the newly formed tube are trimmed. Moreover, with
respect to the use of non-PTFE tape, rather than sintering, the
tape could be solvent bonded, UV bonded or the overlapping portions
could be bonded together through the use of a pressure-sensitive
adhesive.
[0055] The thin tube is then removed from the mandrel. If, because
the tube constricts to some degree during sintering, difficulty is
encountered in removing the tube from the mandrel, several methods
to facilitate removing the tube may be used. Compressed air may be
discharged at one end of the tube between the tube and the mandrel,
or a flat tool may be used to loosen any temporary adhesion between
the mandrel and the tube. Alternatively, a collapsible mandrel or a
bar of reducible diameter may be used. Also, a lubricant such as
silicone, can be introduced to facilitate removal of the tube from
the mandrel.
[0056] The entire stent-graft assembly can also be fabricated in
accordance with method for producing the thin-walled tube utilizing
pressure and heat as discussed above. Specifically, a first tape is
wrapped about the mandrel. Next, the stent is loaded onto the
mandrel over the first tape. A second tape is then wrapped over the
stent. The entire assembly is then placed into a vial which is
packed with microbeads. The assembly is then subjected to pressure
and heat for a sufficient time and at a sufficient temperature to
achieve sintering. Additionally, rather than placing the assembly
in a microbead-filled vial, the membranes of the assembly may be
sintered together by placing the assembly in an oven at
approximately 370.degree. C.
[0057] In the embodiment of the invention shown in FIGS. 4A and 4B,
the materials comprising both the coating (20) and the thin-walled
membrane (21) are typically of chemically similar materials,
preferably polyurethanes, such that when the assembly is subjected
to a solvent, the coating and thin-walled membrane partially
dissolve. The solvent can be introduced via a vapor deposition
process. The assembly can be placed in an enclosed chamber with a
super-saturated atmosphere of solvent. At the plurality of points
at which they are in contact, the coating and thin-walled membrane
dissolve together to form bonding regions in which the coating and
thin-walled membrane become a homogeneous material. In other words,
the coating and thin-walled membrane unite to define a unitary
structure (24). Although a non-porous thin-walled membrane is
depicted in FIGS. 4A through 5d, the thin-walled membrane may be
porous. Suitable solvents include any solvent which will degrade,
dissolve or decrease the viscosity of the coating. Particularly
suitable solvents include but are not limited to dimethyl
acetamide, xylene, and isopropanol.
[0058] In a preferred embodiment of the invention shown in FIGS. 6A
through 7D, the thin-walled membrane comprises a plurality of pores
(32). When the assembly is subjected to an appropriate solvent, the
coating becomes decreasingly viscous. Subject to the ratio of the
solvent to the coating and the relative porosity of the thin-walled
membrane, the coating in this embodiment infiltrates the pores of
the thin-walled membrane to a varying extent. A plurality of
bonding regions (26) at and beyond the surface of the thin-walled
membrane are formed where the coating fills the pores of the
thin-walled membrane and, after the assembly is cured to drive off
the solvent, sealingly engages the thin-walled membrane to the
coating.
[0059] The stent is coated via either a dipping process or a
spraying process. In one embodiment, the spraying process is
performed utilizing a 5.0% solids solution polyurethane in dimethyl
acetamide. The newly coated stent is then cured to remove solvent.
The sequential results of the steps for attaching the coating to a
non-porous graft according to a first method of forming the
thin-walled stent-graft is shown illustratively in FIGS. 5A-5D. A
cross-section of the resulting structure is illustrated in FIG. 4B.
FIGS. 6A and 6B, and FIGS. 7A-7D illustrate the results of the
method when utilizing a porous material for the thin-walled
membrane.
[0060] Further illustrating the method when utilizing a porous
thin-walled membrane, following curing, the coated stent is
expanded to an intermediate diameter, such as by loading it onto an
expansion mandrel, and the thin polymeric tube (21) is mounted over
the exterior of the coated stent, a cross-sectional representation
of which is shown in FIGS. 7B and 7C. The method could have either
the alternative step or the added step of placing a tube within the
stent prior to applying the solvent, such that the resulting
assembly has a thin-walled membrane on the interior of the stent or
on both the interior and the exterior of the stent.
[0061] The assembly is then subjected to a solvent, such as
dimethyl acetamide, which will decrease the viscosity of the
coating and cause it to migrate into the pores of the thin-walled
membrane. The assembly is then cured in a forced air oven to remove
any remaining solvent. The resulting bond is characterized in FIGS.
6A, 6B and 7D, showing a cross-section of a support member (11)
encapsulated in coating, and the coating (20) extending into the
pores of the graft member or thin-walled membrane (21) such that
the coating and thin-walled membrane are in interlocking engagement
with one another. Following the removal of solvent, the device is
configured to its insertion diameter.
[0062] FIG. 8 represents a partial progressive cut-away of another
embodiment of the invention. In the embodiment illustrated in FIG.
8, the assembly comprises a stent (60), a first thin membrane (62)
defining a lumenal surface, a second thin membrane (64) defining a
vascular surface and a coating (65). Because FIG. 8 is a
progressive cut-away illustration, the coating is illustrated as
substantially encapsulating the distal region (68) of the assembly
only, but in actuality encapsulates both the proximal and the
distal regions. The thin-walled membranes may be sintered or
otherwise bonded to one another through the interstices of the
stent. The coating is bonded to the thin-walled membranes in the
same manner as in the previous embodiments.
[0063] FIG. 9 illustrates yet another embodiment of the invention,
as a perspective view of a progressive partial cut-away of this
additional embodiment. In the embodiment depicted in FIG. 9, the
stent (9) comprises a coating (20) substantially covering all of
the support member or members (11). The device further comprises a
thin membrane (21) which in this embodiment defines a vascular
surface (22). The thin membrane (21) is sized such that it covers
the coated stent up to the last stent element (10) on each end of
the stent (9), as shown in FIG. 9. Although, the membrane may
alternatively extend up to and cover at least a portion of the last
stent element. The device further comprises a second coating (34)
which covers the last stent element (10) and at least a portion of
the second to last stent element at both the proximal and distal
regions of the assembly, although illustrated only at the distal
region in FIG. 9.
EXAMPLE 1
[0064] For the purpose of further illustration, an exemplary method
for preparing a thin-walled stent-graft assembly is described as
follows. A thin tape of ePTFE, approximately 0.0004 inch in
thickness, was wound around a 3.25 mm mandrel under slight tension
at approximately a 60 degree angle to the longitudinal axis of the
mandrel. Adjacent edges of the tape overlapped approximately 67 per
cent of the tape's width. The wrapped mandrel was sintered at 370
degrees Celsius for 45 minutes.
[0065] A GFX stent, which is manufactured by Arterial Vascular
Engineering, Inc., in Santa Rosa, Calif., was provided in a 18 mm
length. The end of the stent was mounted on a 0.109 inch diameter
mandrel. The stent was pre-heated at 80 degrees Celsius. The stent
was then sprayed at a rate of 6.3 microliters per second for 10
seconds with a 5.0% solids solution of polyurethane in dimethyl
acetamide. The coated stent was then cured for 90 seconds at 100
degrees Celsius. The procedure was repeated with the opposite end
of the stent mounted on the mandrel.
[0066] Polyurethanes which may be used in accordance with the
present invention include segmented polycarbonate polyurethane such
as that sold under the trademark CHRONOFLEX type AR, which is
available from Cardiotech, Inc., located in Woburn, Mass.
[0067] The thin ePTFE tube was removed from the mandrel and placed
over the coated stent. The stent was then expanded to a 3.5 mm
diameter over an expansion mandrel while inside the thin tube
previously prepared, such that the stent was well opposed to the
graft wall. The stent and graft combination were then placed in a
super-saturated atmosphere of dimethyl acetamide within an enclosed
chamber. The device was then cured in a forced air oven at 80
degrees C. for fifteen minutes. Following curing, the ends of the
stent-graft were trimmed to remove graft material from between the
peaks of the support members. The stent was then configured to its
insertion diameter. Utilizing a fine-tipped syringe dispenser, a
small drop of 5% polyurethane solution was placed on each stent
peak to fully encapsulate the stent member at the peak. The
assembly was again cured for thirty minutes at 80 degrees
Celsius.
EXAMPLE 2
[0068] Utilizing a thin, expanded polytetrafluoroethylene tape of
approximately 0.0004 inch in thickness, the tape was wound
helically around a mandrel from one end of the mandrel and
progressing to the other end under slight tension at an angle of
approximately 50 degrees to the longitudinal axis of the mandrel.
The tape was wound a second time in the opposite direction to form
a second layer, again at an angle of approximately 50 degrees to
the longitudinal axis of the mandrel. Throughout each step of
wrapping the tape, adjacent edges of the tape overlapped
approximately 30 per cent. The wrapped mandrel was then sintered at
a temperature of 370 degrees Celsius for forty-five minutes.
[0069] A GFX coronary bypass stent, which is manufactured by
Arterial Vascular Engineering, Inc., was spray coated with five
microliters per second for five seconds with segmented
polycarbonate polyurethane. The process was performed with the end
of the stent mounted on a mandrel, repeated an additional five
times, each time alternating the end of the stent which was exposed
to the spray. Between each coat, the stent was cured for five
minutes in a forced air oven at 80 degrees C. The coated stent was
then cured in a forced air oven at 80 degrees Celsius for one hour,
and allowed to cool.
[0070] The thin ePTFE tube was removed from the mandrel and placed
over the coated stent. The coated stent was then expanded within
the prepared thin ePTFE tube on an expansion mandrel to 4.5 mm. The
coated stent with graft were then exposed to dimethyl acetamide
solvent via an atomizing spray for one second at a rate 100
microliters per second at 10 second intervals within an enclosed
chamber at ambient temperature for 30 minutes.
[0071] The assembly was then cured at 80 degrees Celsius in a
forced air oven for 30 minutes. Following curing, the ends of the
stent-graft were trimmed to remove graft material from between the
peaks of the support members. The stent was then configured to its
insertion diameter.
[0072] A stent-graft assembly having a thin-walled membrane and
method of manufacturing the same have been disclosed. Although the
present invention has been described in accordance with the
embodiments shown, one of ordinary skill in the art will readily
recognize that there could be variations to the embodiments and
those variations would be within the spirit and scope of the
present invention.
[0073] A wide variety of suitable materials used for stents and
grafts may be interchanged without diverging from the methods or
structures of the invention claimed. For example, the type of stent
utilized could be varied greatly. The embodiments disclosed herein
focus on a stent comprising independent support members, but a
stent which is comprised of a slotted tube or of a rolled film
configuration may also be used. Further, suitable stents include
stents made of nitinol or other shape memory alloy. In order to
confer radiopacity on an alternative stent, various methods may be
utilized. For example, a radiopaque metal marker such as Gold,
Tantalum, Platinum, Iridium or any alloy thereof may be embedded or
encapsulated into the coating of the device.
[0074] A further example of yet another manner of fabricating the
stent-graft assembly involves wrapping a first tape about the
mandrel. Loading the stent onto the mandrel over the first tape.
Wrapping a second tape over the stent. And then applying a hot shoe
proximate the interstices between the stent support members to
sinter the two layers of tape together.
[0075] Suitable membrane material also may include autographs,
which are vessels transplanted within the patient or host;
allografts, which refer to vessels transplanted from a donor which
is a member of the same species as the patient or host; or
xenografts, which are transplanted from a donor which is not a
member of the same species as the patient or host.
[0076] Further, the instant invention can also be used for
indications other than repairing and/or providing radial support to
a body lumen. Other examples include aneurysm isolation and vessel
occlusion. The foregoing embodiments and examples are illustrative
and are in no way intended to limit the scope of the claims set
forth herein.
* * * * *