WO2001052770A1

WO2001052770A1 - Stent-graft assembly and method of making the same

Info

Publication number: WO2001052770A1
Application number: PCT/GB2001/000177
Authority: WO
Inventors: David Granville Stevenson; Linda Ann O'donnell; Kerry Elizabeth Flynn; Karl James Healy
Original assignee: Sulzer Vascutek Limited
Priority date: 2000-01-19
Filing date: 2001-01-18
Publication date: 2001-07-26
Also published as: AU2001228628A1; GB0001102D0

Abstract

A method of manufacture of a stent-graft assembly having at least two extremities, said method comprising the steps of a) providing a covering in tubular form; and b) affixing at least one substantially straight wire-like member to said covering in a pre-determined pattern in order to form a tubular stent structure. The invention also relates to a stent-graft assembly which comprises at least one flexible covering having a tubular form and having at least two extremities. The covering is held in tension by a stent structure which comprises at least one wire-like member provided according a stent pattern, said wire-like member being attached to said covering through attachment points which creates a tension in the covering which forces the covering to form pleats or crimps in an ordered fashion, according to the stent pattern.

Description

Sten -Graft Assembly and method of making the same

The present application concerns an endoluminal graft, more particularly a stent-graft assembly for placement into a stenotic or diseased lumen, especially a vascular lumen. A method of manufacturing the stent-graft assembly is also described.

Stents can be defined as expandable endoprosthesis devices designed for placement into a lumen (such as a blood vessel, bile duct or the like) of a patient's body. The stent reinforces the lumen and maintains its patency. Stents are thus generally used to treat clinical problems such as occluded lumens or weakened lumen walls.

For ease of insertion the stents are expandable devices, being inserted in unexpanded form usually by means of a catheter. Once the stent has been correctly located by the surgeon the stent will be deployed and will adopt its expanded form. The stent may be mechanically expanded (for example by use of a balloon catheter which is inflated from within the lumen of the stent) or alternatively expansion may be achieved through use of a shape memory material, such as nitinol.

Numerous designs of stents have been reported, each aiming to achieve the desired balance of flexibility (to accommodate the natural curvature of the target vessels) with the rigidity required to ensure that the luminal area is maintained. Examples of commercially available stents include the Wallstent (see Sigivant et al, N. Engl . J. Med. , 1987, 316:701-706; and Serruys et al . , N. Engl. J. Med., 1991, 334:13-7), the Palmaz-Schatz stent (see Serruys et al . , N. Engl. J. Med., 1994, 331:489-95; and Fischman et al . , N. Engl. J. Med., 1994, 331:496-501); the Gianturco-Roubin stent (see US-A- 4,580,568 and Roubin et al . , Circulation, 1992, 85:916-27); the Wiktor stent (See Serruys et al . , Cathet. Cardiovascular Diagnosis, 1991, 24:237-45; and DeJaegere et al . , /Am. J. Cardiol., 1993, 72: 165-70); the Multilink (or ACS) stent (see Sigwart et al., Circulation, 1993, 88:1-646 (abstract)), the AVE Micro stent (see Ozaki et al . , Am. J. Cardiol., 1995, 76:112-116) and the NIR stent (see Al ago et al., J. Am. Coll, Cardiol., 1996, 27 (Suppl) : 110A (Abstract) ) .

"Stent-graft" is the term used in the art to refer to metal stents at least partially covered with a lining or sleeve. Stent-grafts were first used clinically in 1991 to treat abdominal aortic aneurysms (see Parodi et al . , Am. Vase Surg., 1991, 5:419-499). The lining or sleeve was introduced to reduce thrombosis and restrict tissue ingrowth that may be caused by scarring the internal walls of the lumen. Suitable materials for the sleeve or lining include Dacron (TM) , nylon, polyester, polytetrafluoroethylene, polyurethene and silicone.

Stent-graft assemblies are described in, for example, US-A-5, 123 , 917 to Lee; US-A-5 , 507 , 771 to Gianturco; 5,628,788 to Pinchuk; US-A-5 , 637 , 113 to Tartaglia; and EP-A-0 , 938 , 879 to Medtronic. In each case, the stent members are formed and are then sewn or glued onto or otherwise affixed to a covering, such as a lining and/or sleeve. Whilst this approach ensures that the stent shape and size is pre-selected exactly as required it is however difficult to achieve a correctly tensioned fit of the covering across the stent scaffold.

Statement of the invention

We have now found that sewing or otherwise affixing a wire-like member onto covering material in tubular form, with the wire following the selected stent pattern, has the benefit of simplicity of manufacture whilst improving the radial tension in the covering at the stent attachment points which forces the covering to form pleats or crimps in an ordered fashion, according to the stent pattern. The ordered crimps or pleats impart considerable flexibility to the covering allowing it to easily accommodate the natural curvature of the target vessels in the body.

An additional benefit is that where the wire is a shape-memory material (such as nitinol) there is no need to heat set the wire to the required stent pattern prior to assembly of the stent-graft assembly.

Thus in one aspect, the present invention provides a stent-graft assembly comprising a flexible covering in tubular form held in tension by a wire-like member attached thereto. As explained above, the wire-like member need not be heat-set.

Thus, instead of providing a pre-shaped (and pre- heat set) wire of the pattern required, locating the pre-shaped wire onto the covering, and then adjoining the covering and pre-shaped wire together to form a stent-graft assembly, the wire can instead be shaped into stent form in situ during its application to the covering.

Thus, the present invention provides a method of manufacture of a stent-graft assembly, said method comprising the steps of:

a) providing a flexible covering in tubular form;

b) shaping at least one wire-like member into a pre-determined pattern whilst affixing the wire-like member to the covering in order to form a tubular stent structure. Preferably the shaping and affixing of the wire-like member creates a radial tension in the covering along the path of the wire-like member forcing the covering to form pleats or crimps in an ordered fashion, according to said pre-determined pattern.

According to another aspect, the invention provides a stent-graft assembly comprising at least one flexible covering having a tubular form, said covering being held in tension by a stent skeleton which comprises at least one wire-like member provided according to a stent pattern, contact between the wire-like member and said covering creating a tension in the covering forcing said covering to form pleats or crimps in an ordered fashion, according to the stent pattern.

Generally, the substantially straight wire-like member will be a metal wire. Suitably the metal wire may be of shape-memory material (for example may be nitinol) and in this case the ability to use non-heat set wire offers a considerable advantage in efficiency of production. Other materials (for example stainless steel) may be used where suitable. Alternatively, the wire-like member may be formed from one or more plastics materials. The stent- graft assembly may comprise only a single wire-like member or may comprise several separate wire-like members (for example up to 10 wire-like members or more, usually 2, 3, 4, 5 or 6 wire-like members) and multiple wire-like members may be required by the stent pattern. The stent-graft assembly may have a plurality of wire-like members running in parallel or formed as a wire braid. This arrangement will allow the resilience of the wire to be maintained while increasing the strength and thus the tensioning force on the fabric covering.

The wire-like member is preferably substantially straight prior to shaping and affixing to the covering. The term "straight" as used herein means that the wire-like member at the time of use will have no kinks or bends along its length that would adversely affect its ability to follow the pre- selected stent pattern. For example, for ease of handling and storage, the wire-like member may be wound around a drum or spool, but any curvature due to that winding will be of a temporary nature and/or will have a radius of curvature which would not prevent the wire being formed into the pattern required during production of the stent-graft assembly.

The term "tubular" used in the description includes multi-tubular conduits, for example "Y" shaped bifurcated conduits used especially to repair specific kind of aneurisms.

For convenience of manufacture the wire-like member will usually be of circular or rounded cross- section, but this is not exclusive and, where appropriate, members of other cross-sectional shapes may be selected. In a preferred embodiment the wire-like member will be a non-preheat set nitinol wire of rounded cross- section and having a diameter of from 0.05mm to 0.5mm, preferably of from 0.12mm to 0.14mm. The covering may be formed from any biocompatible material and mention may be made of polyester, nylon, polytetrafluoroethylene (including expanded PTFE) , polyurethane, silicone and the like. Polyester is preferred.

The covering may be formed from planar material sewn or otherwise formed (for example using glue or the like) into a tube. Alternatively the covering may be woven or knitted in a seamless tubular form. Advantageously the covering will include a longitudinal marker so that any twisting of it during manufacture, on the mandrel or through incorrect attachment of the wire-like member is made readily apparent and can be avoided. The covering may be of any suitable length. Conveniently long lengths of the covering may be formed and then divided into multiple pieces of appropriate length. The diameter of the covering lumen will determine the diameter of the stent-graft assembly. Accordingly, the diameter of the covering lumen will be chosen carefully to accord with the body lumen to be treated. Exemplary sizes include diameters of 5 to 40mm, preferably 8 to 34mm. Whilst the covering may be of uniform diameter, it may alternatively be desirable to include a taper at one or both ends of the covering or along the length of the covering. Preferably the covering is used as a lining, that is to say the wire-like member is attached to the external surface of the covering. In this embodiment the stent skeleton formed by the wire- like member is located on the external surface of the stent-graft assembly. However it is also possible for the covering to be a sleeve with the wire-like member being attached to the internal surface of the covering so that the sleeve forms the external surface of the stent-graft assembly.

In one convenient method of manufacture of the stent-graft assembly herein described, the tubular covering is stretched onto a mandrel . A template depicting the selected stent pattern may then be mounted over the covering. Generally the template will be a stencil and the stent pattern will normally be marked onto the covering using an erasable marker so that the stencil can be removed from the stent-graft assembly. However the template may alternatively be a guiding means which is held in place during attachment of the wire-like member. Alternatively the stent pattern may be programmed into a suitable computer controlled device for positioning the wire. The currently preferred method of attachment of the wire-like member in the pre-selected pattern is by sewing, and for accuracy this will usually be done by hand. Alternatively, the wire-like member may be attached to the covering by adhesive, for example silicone, polyurethane, fluorinated ethylene propylene and the like. It may be desirable to coat the wire-like member prior to attachment to the covering, for example with an anti-coagulant agent, antibiotic or the like. One of the advantages of the present invention is that coating the wire-like member immediately prior to formation of the stent-graft assembly is simple to conduct. Alternatively the whole stent-graft assembly may be coated, if required, for example by dipping or spraying.

For some stent-graft assemblies a second sleeve may be desirable, so that the stent skeleton formed by the wire-like member is completely enclosed. The second sleeve may be stitched to or otherwise attached to the stent and/or the covering as appropriate.

In a further embodiment, it may be desirable to include strengthening rings (for example formed from multiple turns of wire) at each end of the stent- graft assembly.

Brief Description of the drawings

The present invention will now be further described by reference to the Figures in which:

Fig. 1A represents a side-view of a bifurcated stent-graft assembly of the invention, depicting the pattern followed by the wire-like member. Fig. IB depicts the stencil for the stent scaffold pattern for the stent-graft assembly of Fig. 1A.

Fig. 2 represents a side-view of a peripheral stent-graft assembly of the invention, again showing the pattern of the wire-like member .

Fig. 3 shows a stent-graft assembly according to the invention and illustrates the regular crimps achieved in the covering material .

Fig. 4 illustrates the flexibility of the stent- graft assembly of Fig. 3.

Detailed description of preferred embodiments of the invention

In Figures 1A, IB and 2 there is shown a stent-graft assembly 1 where one selected stent pattern 2 is depicted on the covering 3 for the correct positioning of the wire-like member 4. Other stent patterns may alternatively be used. It may be desirable (for ease of manufacture) for the pattern to involve only a single continuous length of wire, but for certain stent patterns, several separate lengths of wire may be required.

Suitable exemplary specifications for a stent-graft assembly according to Fig. 1 are as follows:

A 500mm length of nitinol wire 4 was used to form the stent scaffold in each case. Following attachment of the wire 4 to the covering 3 by handstitching, the bifurcate stitching 5 which extends part way up the length of the stent-graft assembly 1 was inserted.

Suitable exemplary specifications for a peripheral stent-graft assembly 1 according to Fig. 2 are as follows :

In each case the stent wire 4 was hand-sewn onto the covering 3 with 1.0 wax suture and was sewn twice to achieve the required number of stitches per mm.

In both Figs. 1A and 2 the crimping of the material achieved by the tension in the covering at the wire- attachment points is not shown, for clarity. The stent-graft assembly 1 illustrated in Figs. 3 and 4 clearly shows the crimps 6 in covering 3. The crimps 6 occur in an ordered fashion and, as is shown best in Fig. 3, the ordered pattern of the crimps is determined by the selected stent pattern 4 since the increased tension in the covering at the wire attachment points creates the crimps . An important benefit of the stent-graft assembly 1 of the present invention is the creation of the ordered crimps 6 in the covering 3 through the radial tension in the covering 3 along the path of the wire and at the wire attachment points. As shown in Fig. 4 the multiple ordered crimps 6 allow the covering 3 (and thus stent-graft assembly 1) to flex in a controlled manner to accommodate the curvature of the target body lumen.

Modifications and improvements may be made to the foregoing without departing from the scope of the invention.

Claims

Claims :

1. A method of manufacture of a stent-graft assembly, said method comprising the steps of:

a) providing a covering in tubular form; and

b) shaping at least one wire-like member into a pre-determined pattern whilst affixing the wire-like member to the covering in order to form a tubular stent structure.

2. The method of Claim 1, wherein the affixing of the wire-like member creates a radial tension in the covering along the path of the wire-like member forcing the covering to form crimps in an ordered fashion, according to said pre- determined pattern.

3. The method of Claim 1 or 2 , wherein the wire- like member is substantially straight prior to fixing to the covering.

4. The method of any one of Claims 1 to 3 , wherein said wire-like member is a metal wire.

5. The method of any one of Claims 1 to 4 , wherein said metal wire is made of shape-memory material.

6. The method of Claim 5, wherein said shape- memory material is nitinol.

7. The method of any one of Claims 1 to 6 , wherein a plurality of wire-like members are used.

8. The method of Claim 7, wherein the plurality of wire-like members are positioned onto said covering in a parallel relationship.

9. The method of Claim 7, wherein the plurality of wire-like members are positioned onto said covering to form a wire braid.

10. The method of any one of Claim 1 to 9 , wherein said wire-like member is a non-preheat set nitinol wire of rounded cross-section and having a diameter of from 0.05mm to 0.5mm.

11. The method of Claim 10, wherein said diameter ranges from 0.12mm to 0.14mm.

12. The method of any one of Claims 1 to 11, wherein said covering is formed from material selected from polyester, nylon, polytetrafluoroethylene, polyurethane and silicone.

13. The method of any one of Claims 1 to 12, wherein said covering is woven in a seamless tubular form.

14. The method of any one of Claims 1 to 13, wherein said covering has said pre-deter ined pattern marked on it.

15. The method of any one of Claims 1 to 14, wherein said covering is used as a lining and said straight wire-like member is attached to the external surface of said covering.

16. The method of any one of Claims 1 to 15, further including the following steps of:

a) stretching said tubular covering onto a mandrel; and b) mounting a template depicting the selected stent pattern over the covering.

17. The method of any one of Claims 1 to 16, wherein said wire- like member is affixed to said covering according to said pre-selected pattern by sewing.

18. The method of any one of Claims 1 to 17, wherein said wire- like member is coated prior to attachment to the covering.

19. The method of any one of Claims 1 to 18, wherein a second tubular covering is provided on the stent structure created in step b) to enclose said stent structure between said two coverings.

20. The method of any one of Claims 1 to 19, wherein strengthening rings are provided at each extremity of the stent-graft assembly.

21. A stent-graft manufactured according to the method according to any one of Claims 1 to 20.

22. A stent-graft assembly comprising at least one flexible covering having a tubular form, said covering being held in tension by a stent skeleton which comprises at least one wire-like member provided according to a stent pattern, contact between said wire-like member and said covering creating a tension in the covering along the line of contact forcing said covering to form pleats or crimps in an ordered fashion, according to the stent pattern.