CA2536169A1

CA2536169A1 - Stent with improved resistance to migration

Info

Publication number: CA2536169A1
Application number: CA002536169A
Authority: CA
Inventors: Ilya Yampolsky; John Spiridigliozzi
Original assignee: Individual
Current assignee: Boston Scientific Ltd Bermuda
Priority date: 2003-08-19
Filing date: 2004-08-06
Publication date: 2005-03-03
Also published as: JP2007533347A; US7628806B2; JP4750031B2; WO2005018499A8; US20100049291A1; WO2005018499A1; EP1656082A1; US20050043784A1

Abstract

A bifurcated stent comprises a trunk region (22) and at least one branch (24). The trunk region has a balloon expandable section (30) and a self-expandable section (28). The balloon expandable section is less compressible than the self-expandable section. The branch is self-expandable and extends from the self-expandable section of the trunk region. The balloon expandable section is less compressible than the branch.

Description

TITLE
Stent with Improved Resistance to Migration CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates to a stmt for use in body lumens. More io specifically, the present invention relates to a stmt that is sufficiently flexible to facilitate its deployment and conformance to a tortuous lumen, and sufficiently rigid to resist migration, once the stent is deployed.
Description of the Related Art is Stents, grafts, stmt-grafts, vena cava filters and similar implantable medical devices, collectively referred to hereinafter as stems, are radially expandable endoprostheses which are typically intravascular implants capable of being implanted transluminally and enlarged radially after being introduced percutaneously.
Stems may be implanted in a variety of body lumens or vessels such as within the vascular ao system, urinary tracts, bile ducts, etc. Stems may be used to reinforce body vessels and to prevent restenosis following angioplasty in the vascular system. They may be self expanding, mechanically expandable or hybrid expandable.
Stems are generally tubular devices for insertion into body lumens.
However, it should be noted that stems may be provided in a wide variety of sizes and is shapes. Balloon expandable stems require mounting over a balloon, positioning, and inflation of the balloon to expand the stmt radially outward. Self expanding stems expand into place when unconstrained, without requiring assistance from a balloon. A
self expanding stmt is biased so as to expand upon release from the delivery catheter.
Some stems may be characterized as hybrid stems which have some characteristics of 3o both self expandable and balloon expandable stems.

Stems may be constructed from a variety of materials such as stainless steel, Elgiloy, nickel, titanium, nitinol, shape memory polymers, etc. Stems may also be formed in a variety of manners as well. For example a stmt may be formed by etching or cutting the stmt pattern from a tube or section of stem material; a sheet of stmt material may be cut or etched according to a desired stmt pattern whereupon the sheet may be rolled or otherwise formed into the desired substantially tubular, bifurcated or other shape of the stmt; one or more wires or ribbons of stmt material may be woven, braided or otherwise formed into a desired shape and pattern.
Some examples of stems or stmt components that may be braided are io described in U.S. 5061275, U.S. 4655771, U.S. 6146403, U.S. 5836966, U.S.
642308, as well as in U.S. App. No. 10/063315 to Eder et al., filed April 10, 2002.
Typically, a stmt is implanted in a blood vessel or other body lumen at the site of a stenosis or aneurysm by so-called "minimally invasive techniques" in which the stmt is compressed radially inwards and is delivered by a catheter to the is site where it is required through the patient's skin or by a "cut down"
technique in which the blood vessel concerned is exposed by minor surgical means. When the stmt is positioned at the correct location, the catheter is withdrawn and the stmt is caused or allowed to expand to a predetermined diameter in the vessel.
Some stems have been developed specifically to address the problems zo that arise in the treatment of stenoses at or near the site of a bifurcation of a body lumen are known in the art. Further, single bifurcated stems and grafts have been developed in order to treat such conditions at the site of a branch of a body lumen. A
bifurcated stmt and/or graft typically is configured in a "pant" design which comprises a tubular body or trunk and two tubular legs, however other configurations as are also lcnomn wherein the stmt includes a plurality of separate and/or inter-connectable portions which may be delivered to various positions at or around the bifurcation using a single or multiple catheters.
Some examples of bifurcated stents are shown in US 5,723,004; US
4,994,071 and US 5,755,735.
3o In some stems, the compressible and flexible properties that assist in stmt delivery may also result in a stmt that has a tendency to migrate from its originally deployed position. It is thus desirable to provide a stmt configuration that resists migration following deployment, particularly where the site of the desired deployment is within or adjacent to a vessel bifurcation.
All US patents, applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
Without limiting the scope of the invention a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.
io A brief abstract of the technical disclosure in the specification is provided as well only for the purposes of complying with 37 C.F.R. 1.72. The abstract is not intended to be used for interpreting the scope of the claims.
SUMMARY OF THE INVENTION
is The present invention is embodied in a variety of forms. For example in at least one embodiment of the invention a stmt is provided that is adapted both to resist migration within a body lumen and to conform to a tortuous installation path or installed location. The stent includes a first section, typically self expandable, of predetermined compressibility adapted to permit the section to conform to the shape ao of the body lumen through which it is transmitted or surrounding the section when deployed. The stmt also includes a second section which is balloon-expandable and which is less compressible than the first section. The second section is adapted to firmly engage that part of the body lumen surrounding the second section when it is deployed, or to engage the inner surface of another stmt with which it is mated or as assembled upon deployment.
In some embodiments the stmt is a bifurcated stmt. The stmt comprises a trunk region and at least one leg region or branch extending therefrom. In at least one embodiment the trunk defines an opening which defines a first flow path therethrough and one or more branches adjacent thereto, wherein each branch defines 3o additional flow paths.
Where the stmt is bifurcated, the trunk region of the stmt includes a proximal section and a distal section, wherein the branches) extend from the distal section. This distal section of the trunk region, as well as at least a portion of each branch, is constructed from braided strands of material. In some embodiments this braided portion of the stmt is self expandable. The proximal section of the trunk region comprises a solid, tubular geometry with cellular openings to provide a rigid construction within a section of the trunk region of the stmt to assist in resisting migration of the stmt-graft. In some embodiments the proximal section of the trunk region is balloon expandable.
In at least one embodiment, a modular mating stmt is provided that is adapted to resist migration within a receiving stmt. The modular mating stmt includes a substantially self expandable first section of predetermined compressibility io adapted to permit the section to conform to the shape of a body lmnen surrounding the section. The modular mating stent further includes a balloon-expandable second section less compressible than the first section adapted to firmly engage that paxt, i.e.
the inner surface, of the receiving stmt surrounding the second section when the two are assembled in a male-female relationship.
is These and other embodiments which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof.
However, for a better understanding of the invention, its advantages and objectives obtained by its use, reference should be made to the drawings which form a further part hereof and the accompanying descriptive matter, in which there is illustrated and ao described embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
A detailed description of the invention is hereafter described with specific reference being made to the drawings.
as Fig. 1 is a perspective view of an embodiment of the invention comprising a bifurcated stmt.
Fig. 2 is a perspective view of an embodiment of the invention comprising a crimping member that engages the two sections of differential compressibility in the trunk region of the stent of Fig. 1.
3o Fig. 3 is a perspective view of an embodiment of the invention comprising a modular mating stmt adapted to be received within and assembled with a receiving stmt in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION
While this invention may be embodied in many different forms, there are described in detail herein specific preferred embodiments of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated.
For the purposes of this disclosure, like reference numerals in the figures shall refer to like features unless otherwise indicated.
In at least one embodiment of the invention, such as for example the embodiment depicted in Fig. 1, there is shown a bifurcated stmt 20 adapted to resist io migration within a body lumen. Stent 20 includes a trunk region 22 at least one leg region or branches, such as branches 26 and 24, extending therefrom.
The trunk region 22 of stmt 20 includes a first or proximal section 30 and a second or distal section 28. The branches 24 and 26 define separate flow paths which branch from the single flow path defined by the trunk region 22.
is At least a portion of each branch 24 and 26, as well as the distal section 28 of the trunk region 22, share a cormnon predetermined compressibility (or flexibility) adapted to permit the branches 24 and 26 and section 28 to conform to the shape of the body lumens surrounding them at their deployment site and to easily advanced through the tortuous confines of body lumen(s). In at least one embodiment ao the branches 24 and 26 as well as the section 28 are substantially self expandable.
The proximal section 30 of the trunk region 22 is adapted to firmly engage that part of the body lumen surrounding the section 30 at its deployment site adjacent to the bifurcation of a vessel. The section 30 is deployed by mechanical or balloon expansion and is firmly seated within the vessel to resist stmt migration. The as section 30 likewise has a predetermined compressibility, but which is less compressible than that of the distal section 28 or the branches 24 and 26. In some embodiments section 30 is constructed from material having a substantially solid, tubular geometry with cellular openings, which may be obtained from a laser cut tube or sheet which formed into a tube.
3o In some embodiments, the distal section 28 and the branches 24 and 26 are integrally formed of one or more strands 31 of material that are interwoven or braided to form the respective portions of the stmt 20.

The sections 28 and 30 may be bonded, welded, or otherwise engaged together to form the trunk region 22. In at least one embodiment, one or more distal members 33 of the proximal section 30 and one or more proximal members 35 of the distal section 28 are engaged together by at least one crimping members 32 (better seen in Fig. 2). A crimping member 32 comprises a tubular member or band 37 that is disposed about an overlapping portion of one or more distal members 33 and one or more proximal members 35. Once properly disposed, the crimping member is crimped or otherwise compressed in order to fractionally engage and retain the respective portions of members 33 and 35 contained therein.
io In at least one embodiment, during delivery of the stmt 20, when stmt 20 is positioned at the correct location, distal section 28 of the trunk 22 and branches 24 and 26 are caused or allowed to self expand to a predetermined diameter within the vessel(s). Even after the branches 24 and 26 and/or the section 28 are fully expanded, the location of stmt 20 may be adjusted before final placement and fixation.
Once is properly positioned, the proximal section 30 of the trunk 22 is expanded to a predetermined diameter in the vessel via a balloon or other mechanical expansion mechanism such as are known.
Because of the greater rigidity of the proximal section 30, one the proximal section of the trunk 22 is fully expanded the stmt 20 will remain fixed in its ao final position.
As indicated above, when the proximal section 30 is expanded, it is less compressible than the distal section 28 and delivers a substantial radial resistance to force, preventing stmt 20 from working its way away from its originally deployed position.
zs In the embodiment shown in Fig. 1 the distal section 28 and branches 24 and 26 are formed of a conventional material to provide the section 28 and branches 24 and 26 with self expanding characteristics. Suitable materials include, but are not limited to one or more shape-memory metals such as nitinol, one or more shape memory polymers, etc. The proximal section 30 is typically formed of any of a so variety of materials that provide or can be made to provide greater rigidity or compression resistance than that of the distal section 28. Such materials may include but are not limited to stainless steel, nitinol, etc.

During balloon expansion of the proximal section 30, the material or materials of which the section 30 is constructed undergoes plastic deformation to better set the shape induced by the balloon expansion. The tendency of the more rigid section 30, to resist migration may be further enhanced by the inclusion of one or more vessel engagement members 39, a vessel engagement member may be comprised of one or more hooks, barbs, T-fasteners, and/or other external surface features to assist in firmly engaging the surrounding body lumen.
As stated above, the stmt 20 may be a stmt-graft, wherein the stmt 20 is provided with a graft lining or covering to provide fluid pathways from the io unbifurcated end to the bifurcated end.
As mentioned above, an alternative to the balloon-expandable stainless steel proximal section 30 is a balloon-expandable, and thus more rigid, proximal section 30 constructed of nitinol but annealed (i.e., heat treated above the temperature necessary to effect shape-memory retention). Annealing the nitinol transforms its is material properties from a shape memory alloy capable of re-expansion to a more rigid structure, conducive to fixation through alternative means such as balloon expansion.
Fig. 2 is a detail view of crimping member 32 represented in Fig. 1 that secures the two sections of differential compressibility (i.e. section 28 and section 30) together. The exemplary configuration illustrates two braided members 35 of distal ao section 28 secured to one or more members 33 of the proximal section 30 via crimping member 32. In some embodiments crimping member 32 and/or other portions of the stent may be at least partially constructed of one or more radiopaque materials.
As indicated above, stmt 20 is not limited to the use of crimping as members 32 as a securing mechanism between the first and second sections 30 and 38 of the trunk region 22. For example, first section 30 and second section 28 may be secured together via welds, chemical or adhesive bonds, direct mechanical engagement (i.e. hooks, etc.) of the members 33 and 35, and any combinations thereof. Furthermore, the proximal section 30 and distal section 28 may not be 3o connected at all if their relative positions are maintained in some other way, such as by securing section 28 and section 30 each to the inside of a graft, sleeve or other device via sutures or other securement mechanisms such as sutures.

In at least on embodiment, the invention is also directed to a system comprising a modular mating stmt 40 and receiving stmt 42, an example of which is shown in FIG. 3.
The modular mating stmt 40 includes a first section 44 of predetermined compressibility adapted to permit section 44 to conform to the shape of a body lumen surrounding section 44. The modular mating stmt 40 further includes a second section 46 less compressible than first section 44 and adapted to firmly engage that part of receiving stmt 42 surrounding second section 46, i.e. the imier surface of stmt 42 in the area where stmt 40 is received during in vivo deployment and io assembly. A graft 4~ covers modular mating stmt 40 and receiving stmt 42, at least in part, defining a fluid passageway.
The configuration and deployment of this embodiment of the present invention are essentially the same as those of the balloon-expandable embodiment of stmt 20 described previously with reference to Fig. 1. First section 44 is constructed is from braided strands of a shape memory alloy capable of re-expansion, while second section 46 is constructed from a non-shape memory alloy in a tubular geometry with cellular openings. Therefore, placement and fixation are achieved through alternative means such as balloon expansion. A notable difference from stmt 20, however, is that mating stmt 40 is deployed at least partially within receiving stmt 42 as opposed ao to a body lumen, as represented in Fig. 3. The previously described principles of section 30 of stmt 20 firmly engaging the surrounding body lumen apply to second section 46 of modular mating stmt 40 firmly engaging the surrounding receiving stmt 42 to resist migration and leakage.
The above disclosure is intended to be illustrative and not exhaustive.
zs This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the claims where the term "comprising" means "including, but not limited to". Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed 3o by the claims.
Further, the particular features presented in the dependent claims can be combined with each other in other manners within the scope of the invention such that the invention should be recognized as also specifically directed to other embodiments having any other possible combination of the features of the dependent claims. For instance, for purposes of claim publication, any dependent claim which follows should be taken as alternatively written in a multiple dependent form from all prior claims which possess all antecedents referenced in such dependent claim if such multiple dependent format is an accepted format within the jurisdiction (e.g.
each claim depending directly from claim 1 should be alternatively taken as depending from all previous claims). In jurisdictions where multiple dependent claim formats are restricted, the following dependent claims should each be also taken as alternatively written in each singly dependent claim format which creates a o dependency from a prior antecedent-possessing claim other than the specific claim listed in such dependent claim below.

Claims

Claims:

1. A bifurcated stent being expandable from an unexpanded state to an expanded state, the stent comprising:
a trunk region, the trunk region having a balloon expandable section and a self expandable section, in the expanded state the balloon expandable section is less compressible than the self-expandable section; and at least one self-expandable branch extending from the self-expandable section of the trunk region, in the expanded state the balloon expandable section is less compressible than the at least one self-expandable branch.

2. The stent of claim 1 wherein the balloon expandable section of the trunk region comprises a cut tube of stent material comprising a plurality of interconnected members defining a plurality of cell spaces.

3. The stent of claim 1 wherein the balloon expandable section of the trunk region comprises a cut sheet of stent material formed into a tubular shape, the tubular shape comprised of a plurality of interconnected members defining a plurality of cell spaces.

4. The stent of claim 1 wherein the self expandable section of the trunk region and at least a portion of the at least one self-expandable branch is at least partially constructed from at least one strand of braided stent material.

5. The stent of claim 1 wherein the balloon expandable section of the trunk region comprises at least one distally extending member and the self-expandable section of the trunk region comprises at least one proximally extending member, the at least one proximally extending member and the at least one distally extending member being engaged to each other.

6. The stent of claim 5 further comprising at least one crimping member, the at least one crimping member disposed about the at least one proximally extending member and the at least one distally extending member.

7. The stent of claim 6 wherein the at least one crimping member is at least partially constructed of a radiopaque material.

8. The stent of claim 1 wherein the balloon expandable section of the trunk region is at least partially constructed of stainless steel.

9. The stent of claim 1 wherein at least one of the self-expandable section of the trunk region and the at least one self-expandable branch is at least partially constructed of a shape memory material

10. The stent of claim 10 wherein the shape memory material is nitinol.

11. The stent of claim 1 further comprising at least one vessel engagement member, the at least one vessel engagement member extending from at least a portion of the balloon expandable section, the at least one vessel engagement member selected from the group consisting of hooks, barbs, T-fasteners, bumps, ridges, and any combination thereof.

12. The stent of claim 1 further comprising at least one layer of graft material, the at least one layer of graft material positioned on at least one of an inside surface and outside surface of at least a portion of at least one of the trunk region and the at least one self-expandable branch to define a fluid passageway therethrough.

13. A modular mating stent adapted to resist migration within a receiving stent, comprising:
a substantially self-expandable first section of predetermined compressibility adapted to permit said section to conform to the shape of a body lumen surrounding said section; and a balloon-expandable second section less compressible than said first section adapted to firmly engage a surface of the receiving stent surrounding the second section.

14. The modular mating stent of claim 13 wherein the second section is comprised of a tubular member, the tubular member defining a plurality of openings.

15. The modular mating stent of claim 14 wherein the first section is at least partially constructed from nitinol and the second section is at least partially constructed from stainless steel.

16. The modular mating stent of claim 14 wherein the second section comprises at least one vessel engagement member, the at least one vessel engagement member selected from the group consisting of hooks, barbs, or T-fasteners.

17. The modular mating stent of claim 14 further comprising a graft cover, the graft cover at least partially disposed about an/or within the modular mating stent to define a fluid passageway therethrough.