U.S. patent application number 10/643527 was filed with the patent office on 2004-03-18 for composite vascular graft.
This patent application is currently assigned to Scimed Life Systems, Inc.. Invention is credited to Brodeur, Christopher Brian, Smith, Scott.
Application Number | 20040054397 10/643527 |
Document ID | / |
Family ID | 23362798 |
Filed Date | 2004-03-18 |
United States Patent
Application |
20040054397 |
Kind Code |
A1 |
Smith, Scott ; et
al. |
March 18, 2004 |
Composite vascular graft
Abstract
A composite stent/graft tubular prosthesis includes an inner
PTFE tubular structure, an outer PTFE tubular structure assembled
about the inner PTFE tubular structure, and a circumferentially
distensible stent interposed between the inner and outer PTFE
tubular structures. The outer tubular body is a non-continuous body
formed of polytetrafluoroethylene components, providing axial and
circumferential compliance to said prosthesis. The outer tubular
body completely overlies the distensible stent.
Inventors: |
Smith, Scott; (Chaska,
MN) ; Brodeur, Christopher Brian; (Blaine,
MN) |
Correspondence
Address: |
HOFFMANN & BARON, LLP
6900 JERICHO TURNPIKE
SYOSSET
NY
11791
US
|
Assignee: |
Scimed Life Systems, Inc.
|
Family ID: |
23362798 |
Appl. No.: |
10/643527 |
Filed: |
August 19, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10643527 |
Aug 19, 2003 |
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09347218 |
Jul 2, 1999 |
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6652570 |
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Current U.S.
Class: |
623/1.13 ;
623/1.53 |
Current CPC
Class: |
A61F 2/89 20130101; A61F
2/90 20130101; A61F 2/07 20130101; A61F 2002/075 20130101; A61F
2220/0058 20130101; A61F 2220/0075 20130101 |
Class at
Publication: |
623/001.13 ;
623/001.53 |
International
Class: |
A61F 002/06 |
Claims
What is claimed is:
1. An implantable composite intraluminal prosthesis comprising: a
substantially continuous polytetrafluoroethylene tubular inner
body; a longitudinally non-continuous outer tubular body; and a
circumferentially distensible support structure interposed between
the inner and outer tubular bodies, said outer tubular body being
formed of polytetrafluoroethylene components, having a longitudinal
length and a width, said longitudinal length being greater than
said width, said components completely overlying the dispensable
support structure, whereby axial and circumferential compliance is
provided to said prosthesis.
2. A composite intraluminal prosthesis according to claim 1 wherein
the outer polytetrafluoroethylene body comprises a
polytetrafluoroethylene tape spirally wrapped with a plurality of
helical turns in a circumferential direction around the inner
tubular body and distensible support structure, wherein each
helical turn of said spiral wrap defines one of said
polytetrafluoroethylene components.
3. A composite intraluminal prosthesis according to claim 1 wherein
the outer polytetrafluoroethylene body comprises segments of
polytetrafluoroethylene tape, each wrapped circumferentially around
the inner tubular body and distensible support structure wherein
each turn of said segments defines one of said
polytetrafluoroethylene components.
4. A composite intraluminal prosthesis according to claim 1 wherein
the outer polytetrafluoroethylene body comprises first and second
polytetrafluoroethylene tapes interweaved through each other around
the inner tubular body, said first and second tapes defining said
components.
5. A composite intraluminal prosthesis according to claim 1 wherein
the outer tubular body comprises three or more
polytetrafluoroethylene tapes arranged in a braided tubular
configuration, said three or more tapes defining said
components.
6. A composite intraluminal prosthesis according to claim 4 or 5
wherein a sealant is interspersed between said tapes.
7. A composite intraluminal prosthesis according to claim 1 wherein
said continuous polytetrafluoroethylene tubular inner body is
comprised of a sheet of expanded polytetrafluoroethylene formed
into a tubular shape by wrapping said sheet about a longitudinal
axis.
8. A method of providing axial and circumferential compliance to an
intraluminal prosthesis stent/graft composite comprising: combining
a non-continuous polytetrafluoroethylene tubular outer body over a
substantially continuous polytetrafluoroethylene tubular inner
body, wherein said outer body and inner body support a distensible
support structure therebetween, said outer body completely covering
the distensible support structure, said outer body is formed by
tubularly-assembled polytetrafluoroethylene components.
9. A method according to claim 8 wherein the non-continuous outer
tubular body is formed by spirally wrapping a
polytetrafluoroethylene tape with a plurality of helical turns in a
circumferential direction around the inner tubular body and
distensible support structure to form an outer tubular body,
wherein each helical turn of said spiral wrap defines one of said
polytetrafluoroethylene components.
10. A method according to claim 8 wherein the non-continuous outer
tubular body is formed by circumferentially wrapping segments of a
polytetrafluoroethylene tape around the inner tubular body and
distensible support structure to form an outer tubular body wherein
each circumferential turn of said segments defines one of said
polytetrafluoroethylene components.
11. A method according to claim 8 wherein the outer tubular body is
formed by interweaving first and second polytetrafluoroethylene
tapes through each other and about the continuous
polytetrafluoroethylene inner tubular body and distensible support
structure wherein said first and second tapes define said
components.
12. A method according to claim 8 wherein the outer tubular body is
formed by arranging three or more polytetrafluoroethylene tapes in
a braided configuration, wherein said three or more tapes define
said components.
13. A method according to claim 11 or 12 wherein a sealant is
interspersed between said tapes.
14. A method according to claim 8 wherein the substantially
continuous polytetrafluoroethylene tubular inner body is formed by
wrapping a sheet of polytetrafluoroethylene around a mandrel into a
tubular structure.
15. A method of providing axial and circumferential compliance to
an intraluminal prosthesis stent/graft composite, comprising:
combining a polytetrafluoroethylene strip and a distensible support
structure to form an assembly strip; and combining said assembly
strip with a substantially continuous inner tubular body support by
wrapping said assembly strip about said inner tubular body support
in a non-overlapping pattern, such that the assembly strip
completely covers the distensible support structure forming a
non-continuous outer tubular body of polytetrafluoroethylene
components.
16. The method of claim 15 wherein segments of said assembly strip
are wrapped circumferentially about said inner tubular body
support, to form a non-continuous outer tubular body of
polytetrafluoroethylene components.
17. The method of claim 15 wherein the polytetrafluoroethylene
strip is a tape.
18. The method of claim 17, wherein the assembly strip is wrapped
with a plurality of helical turns around the inner tubular body,
each helical turn defining one of said polytetrafluoroethylene
components.
19. A method of making an implantable intraluminal stent/graft
composite prosthesis comprising: a) providing a continuous ePTFE
tubular inner body; b) wrapping a stent about said continuous ePTFE
tubular inner body, in a non-overlapping relationship; and c)
wrapping an ePTFE strip about the tubular inner body and stent, to
completely overly the stent.
20. A method of making an implantable intraluminal stent/graft
prosthesis, comprising: a) providing an ePTFE strip, having a
length greater than its width; b) providing an unwrapped stent; c)
assembling the stent with the strip to make an assembly strip with
a stent side and an ePTFE strip side; d) providing a continuous
tubular inner body; and e) wrapping the assembly strip around the
inner body in non-overlapping relationship, such that the stent is
completely covered.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to a tubular
implantable prosthesis formed of porous expanded
polytetrafluoroethylene. More particularly, the present invention
relates to a composite, multi-layered endoprosthesis having
increased axial and radial compliance.
BACKGROUND OF THE INVENTION
[0002] An intraluminal prosthesis is a medical device commonly
known to be used in the treatment of diseased blood vessels. An
intraluminal prosthesis is typically used to repair, replace, or
otherwise correct a damaged blood vessel. An artery or vein may be
diseased in a variety of different ways. The prosthesis may
therefore be used to prevent or treat a wide variety of defects
such as stenosis of the vessel, thrombosis, occlusion, or an
aneurysm.
[0003] One type of endoluminal prosthesis used in the repair of
diseases in various body vessels is a stent. A stent is a generally
longitudinal tubular device formed of biocompatible material which
is useful to open and support various lumens in the body. For
example, stents may used in the vascular system, urogenital tract
and bile duct, as well as in a variety of other applications in the
body. Endovascular stents have become widely used for the treatment
of stenosis, strictures, and aneurysms in various blood vessels.
These devices are implanted within the vessel to open and/or
reinforce collapsing or partially occluded sections of the
vessel.
[0004] Stents are generally open ended and are radially expandable
between a generally unexpended insertion diameter and an expanded
implantation diameter which is greater than the unexpended
insertion diameter. Stents are often flexible in configuration,
which allows them to be inserted through and conform to tortuous
pathways in the blood vessel. The stent is generally inserted in a
radially compressed state and expanded either through a
self-expanding mechanism, or through the use of balloon
catheters.
[0005] A graft is another type of commonly known type of
intraluminal prosthesis which is used to repair and replace various
body vessels. A graft provides an artificial lumen through which
blood may flow. Grafts are tubular devices which may be formed of a
variety of material, including textiles, and non-textile materials.
One type of non-textile material particularly useful as an
implantable intraluminal prosthesis is polytetrafluoroethylene
(PTFE). PTFE exhibits superior biocompatability and low
thrombogenicity, which makes it particularly useful as vascular
graft material in the repair or replacement of blood vessels. In
vascular applications, the grafts are manufactured from expanded
polytetrafluoroethylene (ePTFE) tubes. These tubes have a
microporous structure which allows natural tissue ingrowth and cell
endothelization once implanted in the vascular system. This
contributes to long term healing and patency of the graft. These
tubes may be formed from extruded tubes or may be formed from a
sheet of films formed into tubes.
[0006] Grafts formed of ePTFE have a fibrous state which is defined
by interspaced nodes interconnected by elongated fibrils. The
spaces between the node surfaces that is spanned by the fibrils is
defined as the intemodal distance (IND). Porosity of a graft is
measured generally by IND. In order of proper tissue ingrowth and
cell endothelization, grafts must have sufficient porosity obtained
through expansion. When the term expanded is used to describe PTFE,
it is intended to describe PTFE which has been stretched, in
accordance with techniques which increase IND and concomitantly
porosity. The stretching may be in uni-axially, bi-axially, or
multi-axially. The nodes are spaced apart by the stretched fibrils
in the direction of the expansion. Properties such as tensile
strength, tear strength and radial (hoop) strength are all
dependent on the expansion process. Expanding the film by
stretching it in two directions that are substantially
perpendicular to each other, for example longitudinally and
transversely, creates a biaxially oriented material. Films having
multi-axially-oriented fibrils may also be made by expanding the
film in more than two directions. Porous ePTFE grafts have their
greatest strength in directions parallel to the orientation of
their fibrils. With the increased strength, however, often comes
reduced flexibility.
[0007] While ePTFE has been described above as having desirable
biocompatability qualities, tubes comprised of ePTFE, as well as
films made into tubes, tend to exhibit axial stiffness, and minimal
radial compliance. Longitudinal compliance is of particular
importance to intraluminal prosthesis as the device must be
delivered through tortuous pathways of a blood vessel to the
implantation site where it is expanded. A reduction in axial and
radial flexibility makes intraluminal delivery more difficult.
[0008] Composite intraluminal prosthesis are known in the art. In
particular, it is known to combine a stent and a graft to form a
composite medical device. Such composite medical devices provide
additional support for blood flow through weakened sections of a
blood vessel. In endovascular applications the use of a composite
graft or a stent/graft combination is becoming increasingly
important because the combination not only effectively allows the
passage of blood therethrough, but also ensures patency of the
implant. But, composite prosthesis, especially those consisting of
ePTFE, while exhibiting superior biocompatability qualities, also
exhibit decreased axial and radial compliance. It is therefore
desirable to provide an ePTFE composite intraluminal prosthesis
which exhibits increased axial and radial compliance.
SUMMARY OF THE INVENTION
[0009] The present invention comprises a composite ePTFE vascular
prosthesis. The composite has three layers; an inner tubular ePTFE
layer, a discontinuous outer layer, and a radially deformable stent
atop the inner tubular layer and entirely beneath the outer
layer.
[0010] One advantage of the present invention is that it provides
an improved composite ePTFE intraluminal prosthesis exhibiting
increased axial and circumferential compliance and flexibility and
greater tissue ingrowth.
[0011] Another advantage of the present invention is that it
provides an improved stent/graft combination, exhibiting increased
axial and circumferential compliance and flexibility.
[0012] Another advantage ofthe present invention is that it
provides an improved composite ePTFE intraluminal prosthesis
exhibiting increased axial and circumferential compliance and
flexibility and greater tissue ingrowth through the use of
multiaxial fibril direction in a non-continuous outer ePTFE tubular
body.
[0013] It is yet another advantage of the present invention to
provide an improved method of forming such composites using
preassembled graft/stent strips.
[0014] The present invention provides a composite intraluminal
prosthesis for implantation which may have a substantially
continuous ePTFE tubular inner body in combination with a
non-continuous outer ePTFE tubular body formed by tubularly
assembled polytetrafluoroethylene strips, or components. A
circumferentially distensible support structure is interposed
between the two PTFE layers. The components or strips comprising
the outer tubular body possess a longitudinal length and a width,
with said longitudinal length being greater than said widths; the
non-continuous, tubular assembled strips providing axial and
circumferential compliance to said prosthesis.
[0015] A method of forming an intraluminal prosthesis stent/graft
with axial and circumferential compliance is provided by combining
a non-continuous PTFE tubular outer body over a substantially
continuous PTFE tubular inner body, said outer body and inner body
supporting a stent thereinbetween. Use of a braided or woven PTFE
in at least the outer layer enhances the axial and circumferential
compliance, and provides puncture sealing properties to prosthesis
of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a perspective showing of a tubular structure which
may be used as the inner tubular structure of the prosthesis of the
present invention.
[0017] FIG. 2 is a perspective view of an assembly strip of the
present invention, including a planar graft strip and an undulating
wire stent, for forming a composite stent/graft prosthesis
according to the present invention.
[0018] FIG. 2A is a perspective showing, partially in section of a
portion, of the composite stent/graft prosthesis of the present
invention.
[0019] FIG. 2B is a perspective showing of another stent/graft
composite prosthesis of the present invention.
[0020] FIG. 3 is a perspective view of an assembly strip of the
present invention, including a planar graft strip and a
substantially linear wire stent, for forming the composite stent
graft prosthesis according to the present invention.
[0021] FIG. 3A is a perspective showing of a portion of a composite
stent/graft prosthesis of the present invention.
[0022] FIG. 4 shows a partial perspective of the stent and exterior
surface of the outer PTFE tubular body of another embodiment of the
present invention.
[0023] FIG. 5 shows an enlarged perspective view of the exterior
surface of another embodiment of the outer PTFE tubular body.
[0024] FIG. 6 shows an enlarged perspective of the exterior surface
of another embodiment of the outer PTFE tubular body.
DETAILED DESCRIPTION OF THE INVENTION
[0025] The prosthesis of the preferred embodiment of the present
invention is a composite implantable intraluminal prosthesis which
is particularly suited for use as a vascular graft. The composite
prosthesis of the present invention includes a multi-layer graft
structure with radially deformable stent interposed between layers.
The present description is meant to describe the preferred
embodiments, and is not meant to limit the invention in any
way.
[0026] Shown in FIG. 1 is a continuous tubular inner PTFE body 2
which may form one of the layers of the multilayer graft. The
braided tubular body is formed by wrapping a PTFE sheet 4 around a
mandrel (not shown), to form a tubular body with a seam 6
longitudinally therealong. The seam in the tube may be bonded
thermally, adhesively, or with the use of a polymeric solution. It
may be fully or partially bonded. Furthermore, the tube may consist
of one single layer of the wrap as shown in FIG. 1, or it may
consist of multiple windings of the PTFE sheet around the
longitudinal axial to create a multi-layer inner tube.
[0027] While in the preferred embodiment, tubular body 2 is formed
from a wrapped PTFE sheet, tubes of extruded PTFE may be used to
form the continuous inner tubular body of the present
invention.
[0028] Continuous, as used herein, refers to a tubular structure
whose surface extends substantially uninterrupted throughout the
longitudinal length thereof. In the case of an extruded tube, the
tubular structure is completely uninterrupted. In the case of a
sheet formed tube there are no transverse interruptions. As is
known in the art, a substantially uninterrupted tubular structure
exhibits enhanced strength and sealing properties when used as a
vascular graft.
[0029] FIG. 2 depicts an assembly strip 8 for forming a composite
stent/graft prosthesis 11 according to the present invention. The
assembly strip 8 comprises a planar graft strip 10 and a radially
deformable support structure such as planar stent 12 in this
embodiment, an undulating wire stent 14. Distensible, as used
herein, refers to a stent which may be expanded and contracted
radially. The stent 12 may be temporarily fastened to the strip, or
simply assembled therewith. The composite prosthesis 11 is made by
wrapping the assembly strip about a tubular inner PTFE body 2, and
securing the graft strip directly to the tubular graft body. As
shown in FIG. 2A, preferably the strip is wound helically around
the tubular inner body 2. One preferred construction for assembly
strip 8 is shown and described in commonly assigned U.S. patent
Application, entitled "Helically Formed Stent/Graft Assembly" and
filed at even date herewith. This application is incorporated by
reference herein. In an alternate construction depicted in FIG. 2B,
individual assembly strips, 8', are joined at seams 6' in an
annular fashion to form a plurality of spaced apart stent/graft
covers over tubular body 2.
[0030] Various stent types and stent constructions may be employed
in the invention. Among the various stents useful include, without
limitation, self-expanding stents and balloon expandable extents.
The stents may be capable of radially contracting, as well, and in
this sense can best be described as radially distensible or
deformable. Self-expanding stents include those that have a
spring-like action which causes the stent to radially expand, or
stents which expand due to the memory properties of the stent
material for a particular configuration at a certain temperature.
Nitinol is one material which has the ability to perform well while
both in spring-like mode, as well as in a memory mode based on
temperature. Other materials are of course contemplated, such as
stainless steel, platinum, gold, titanium and other bicompatible
metals, as well as polymeric stents.
[0031] The configuration of the stent may also be chosen from a
host of geometries. For example, wire stents can be fastened into a
continuous helical pattern, with or without a wave-like or zig-zag
in the wire, to form a radially deformable stent. Individual rings
or circular members can be linked together such as by struts,
sutures, welding or interlacing or locking of the rings to form a
tubular stent. Tubular stents useful in the present invention also
include those formed by etching or cutting a pattern from a tube.
Such stents are often referred to as slotted stents. Furthermore,
stents may be formed by etching a pattern into a material or mold
and depositing stent material in the pattern, such as by chemical
vapor deposition or the like.
[0032] In constructing the composite intraluminal prosthesis 11 of
FIG. 2A, it is not necessary to preassemble strips 8. In one method
of construction, the inner tubular body 2 is circumferentially
enclosed by stent 12. The stent 12 may be formed from an elongate
wire 14 which is helically wound with a plurality of longitudinally
spaced turns into an open tubular configuration. The stent may be
of the type described in U.S. Pat. No. 5,575,816 to Rudnick, et al.
Stent 12 is an expandable tubular member which may be either of the
balloon-expanded or self-expanded type. Stents of this type are
typically introduced intraluminally into the body, and expanded at
the implantation site.
[0033] The composite endoluminal prosthesis 11 is completed by
wrapping strip(s) of ePTFE over the stent, to make a non-continuous
outer PTFE tubular body 16 which circumferentially surrounds the
inner tube 2 and the stent 12. Non-continuous, as used herein,
refers to a tubular structure which is not substantially
uninterrupted along its length as it contains at least two spaced
apart edges 18 and 18a transverse to the longitudinal surface of
the tubular body. The non-continuous outer PTFE tubular body 16 is
comprised of a flat PTFE tape helically wound around the inner tube
2 and stent 12 so as to completely overly the stent.
[0034] The outer body 16 possesses edges 18 which define the
separate PTFE components, and edges 18a define open spaced in the
outer PTFE tubular body 16. The PTFE components shown in outer tube
16 consist of the successively spaced helical turns 16a of an
axially wrapped PTFE tape 10. Prior to winding, the PTFE tape 10
has a substantially flat cross-section, and a longitudinal length
substantially longer than the width of the tape.
[0035] Referring now to FIG. 2B, the composite endoluminal
prosthesis may be alternatively constructed by winding individual
stent sections 12' axially about tube 2, and overlying the stent
sections with strips 10', or cutting preassembled strip sections 8'
and seaming them at 6'. The embodiment of FIG. 2B is also
non-continuous defining spaced apart edges 18 identifying open
spaces therebetween.
[0036] FIG. 3 shows an alternate assembly strip construction 19
comprising a planar graft strip 20 assembly with a stent 21, which
in this embodiment is a substantially straight wire. In assembling
a composite endoluminal prosthesis from assembly strip 19, the
strip may be helically wound in a non-overlapping configuration
about inner tubular member 2 in a manner similar to that described
with respect to FIG. 2A. Tape 20 may be secured to inner tubular
body 2, sealing the stent within the composite. Alternatively, the
stent may be wound about the inner tubular member, and graft strip
20 laid atop the stent. It should also be noted that assembly strip
19 may be cut into segments, each of which may be wound
circumferentially about the tube body 2, and seamed in a manner
similar to that described with respect to FIG. 2B.
[0037] FIG. 4 depicts a further embodiment of the present invention
which also provides a non-continuous outer tube. This embodiment
employs an inner tube 2 and a stent 12 as described above in
relation to FIGS. 2 and 2A. In this preferred embodiment, the
composite prosthesis 22 possesses an outer tubular body 24
including a weave, or a braid of individual PTFE tapes. The woven
or braided configuration may be two dimensional or may be three
dimensional, as shown in FIGS. 5 and 6.
[0038] FIG. 5 shows two PTFE tapes combined in a two dimensional
matrix, wherein the two tapes comprise the separate components of
the non-continuous tubular body 24.
[0039] FIG. 6 shows an enlarged view of a three dimensional braid
comprised of three PTFE tapes braided together in three directions.
Such braided, knitted or woven construction provides axial and
radial compliance to the prosthesis 22 by defining spaces within
the braided, knitted or woven extruded structure.
[0040] In certain applications where enhanced sealing properties
are required, a sealant 28, as shown in FIG. 6, may be interspersed
within the woven or braided matrix to create a non-porous outer
tubular body. Sealants which may be used in the prosthesis include
FEP, polyurethane, and silicone. Additional sealants include
biological materials such as collagen, and hydrogels,
polymethylmethacrylate, polyamide, and polycarbonate. Elastomers as
sealants will have less impact on flexibility. A suitable sealant
provides a substantially sealed outer tube without significantly
reducing longitudinal and axial compliance.
[0041] As shown herein the outer tubular body shown in the
above-referenced figures form non-continuous bodies comprised of
PTFE components tubularly assembled. The non-continuous structure
of the outer tubular body provides the composite prosthesis with
enhanced radial and longitudinal, or axial compliance. The radial
and axial compliance can, in fact, be varied with the different
outer PTFE bodies which may be used, as may be suitable for the use
of the intraluminal prosthesis. The non-continuous outer layer 16
is formed by wrapping one, two, or three or more PTFE tapes in an
axial wrap, weave, braid or other non-continuous tubular body
consisting of the component PTFE parts defined above.
[0042] In preferred embodiments the PTFE tape forming the PTFE
components is expanded PTFE (ePTFE). The term expanded refers to
PTFE which has been stretched uniaxially, biaxially, or
multiaxially in a particular direction. The PTFE tape of the
prosthesis of the present invention is typically stretched in the
longitudinal direction of the tape. When two or more tapes are
combined to form the outer tubular body, the resultant tubular body
possesses a biaxial, or multiaxial resultant orientation in the
aggregate. Because ePTFE exhibits increased strength in the
direction of its stretching, the ePTFE tubularly assembled body
exhibits the advantage of the increased strength of a biaxial or
multiaxial stretched film, but exhibits the advantages of
compliance because of its non-continuous surface.
[0043] The inner PTFE tubular layer may be bonded to the outer PTFE
tubular layer through spaces in the open wall of the stent. The
bonding may be effectuated with the use of an adhesive, or by
adhering the layers together without an adhesive. Bonding of the
PTFE layers without an adhesive may take place by such methods as
laminating, or sintering of the prosthesis. Furthermore, the stent
may be adhered to the inner PTFE tubular layer, the outer PTFE
tubular layer, or both. Similarly, such adherence may take place
with or without the use of an adhesive.
[0044] Although illustrative embodiments of the present invention
have been described herein with reference to the accompanying
drawings, it is to be understood that the invention is not limited
to those precise embodiments, and that various other changes and
modifications may be effected therein by one skilled in the art
without departing from the scope or spirit of the invention.
* * * * *