WO2005107394A2

WO2005107394A2 - Method of fenestrating endovascular stent support elements

Info

Publication number: WO2005107394A2
Application number: PCT/US2005/014938
Authority: WO
Inventors: James H. Layer; Jose Fernandez
Original assignee: Gmp/Cardiac Care, Inc.
Priority date: 2004-04-30
Filing date: 2005-04-29
Publication date: 2005-11-17
Also published as: WO2005107394A3

Abstract

A method of fenestrating the support structures (4) of an endovascular stent (100) at desired locations and in a desired pattern within the stent is disclosed, with increased efficiency, economy, and reliability over conventional manufacturing techniques. Such fenestrations (9) may be used to allow placement of longitudinal rails (7) throughout some or all of the length of the stent to improve stent flexibility and strength while retaining or improving upon other desirable qualities of existing endovascular stents.

Description

METHOD OF FENESTRATING ENDOVASCULAR STENT SUPPORT ELEMENTS

TECHNICAL FIELD

[001] The present invention relates generally to the field of endovascular medical devices, and relates more specifically to a method for fabricating a stent for use in supporting vascular tissue, and particularly, to a method for drilling holes through the support elements of such a stent.

BACKGROUND ART

[002] It is generally known to insert a resiliently expandable stent into a blood vessel to provide radial vascular support (hoop support) within the vessel in the treatment of atherosclerotic stenosis. For example, it is generally known to open a blocked cardiac blood vessel by known methods (e.g., balloon angioplasty or laser ablation) and to keep that blood vessel open using such a stent. These stents are generally formed of a biocompatible material, such as stainless steel, and have slots or holes cut therein or have an expansile mesh design, so that an operator may expand the stent after it has been deployed into a blood vessel.

[003] Stents with increased longitudinally flexibility over conventional designs are disclosed, for example, in U.S. Patent Application Publication Nos. 2002/0138131 and 2004/0106975 both of which are incorporated herein by reference. The stents discussed in these references generally include a plurality of independent circumferential vascular "support elements'¹, sometimes referred to as "hoops" or "rings", mounted on one or more flexible "longitudinal rail" elements that extend along the length of the stent. In some embodiments of longitudinally flexible stents, the support elements are all part of a continuous helically wound element and are also freely mounted on one or more flexible rail elements that extend along the length of the stent. In other embodiments, the stent includes a plurality of circumferential or helical support elements each connected to at least one adjacent support element through a connecting "bridge" structure and also freely mounted on rail elements.

[004] In the above examples, the support elements are free to move along the rail element and thus alter the spacing between the support elements to conform to any curvature in the blood vessel in which they are placed. In this manner, the stent can more easily conform to the bend in the blood vessel and reduce the tendency of the stent to straighten the blood vessel, something that is generally undesirable.

[005] The use of a longitudinal rail in which the support elements can freely move requires placement of the rail through a fenestration placed through at least two of such support elements, but often multiple support elements throughout the length of the stent. In order to preserve the shape of the stent, the support element fenestrations must be precisely placed so that they occur at the same radial location on every support element. In other words, when viewing the stent from one of its ends, the fenestrations for each of the rails must line up so that there is a continuous straight path through the stent from one end to the other. ^"[006] Conventionally, placement on the support elements of such high- precision fenestrations requires the manufacture of the stent in multiple segments. This limitation is caused by the need to utilize conventional mechanical drilling or electrical discharge machining (EDM) to create the high-precision fenestrations. Due to limitations in the respective technologies, neither of the above-mentioned conventional methods of creating the fenestrations is capable of placing fenestrations with precision on more than a few contiguously located support elements. As a consequence, conventionally, stents that require such fenestrations in their support elements must be manufactured in a multiple-step process involving first the manufacture of relatively short stent segments with few support elements, next the fenestration by EDM or mechanical drilling of the

^■ support elements and finally the assembly of the multiple short stent segments into a stent of the required size for a particular application.

[007] Manufacture of stents by segments is costly, requiring separate fabrication and assembly stages. Moreover, segmental assembly of stents may result in reduced structural strength, as the potential exists for areas of weakness at the sites where segments are welded or otherwise joined. Finally, conventional machining and EDM are limited in their ability to manufacture stents with very small holes through the stent walls.

[008] Thus, the need exists for improved manufacturing techniques that will provide a more efficient, reliable, and economical means of placing fenestrations through the support elements of an endovascular stent, so that a rail may be placed therethrough for increased longitudinal flexibility over existing stents.

DISCLOSURE OF INVENTION [009] It is an object of the present invention to overcome, or at least alleviate, one or more of the difficulties or deficiencies associated with prior art manufacturing methods for endovascular stents with longitudinal rails. In that regard, the present invention provides various methods to fenestrate a stent in a desired manner longitudinally throughout all or some of its length.

[010] Such longitudinal fenestrations can then be used to receive longitudinal rails which may impart increased flexibility and strength to the resulting stent.

[011] In that regard, the present invention fulfills in part the need to fabricate an endovascular stent in whole or in part with aligned fenestrations of desired size, location, and shape in a manner that is not limited by the length of the sent, all while producing a stent with radial strength equal to or greater than existing endovascular stents.

[012] These and other features, aspects, and other advantages of the present invention will become better understood with regard to the following drawings, description, and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[013] FIG. 1 provides a perspective view of an endovascular stent in its expanded condition including circumferential support elements, bridge structures, longitudinal and aligned fenestrations according to the present invention. [014] FIG. 2 provides an isolated perspective view of a circumferential support element of a stent with fenestrations according to the present invention in its unexpanded condition.

[015] FIG. 3 provides a side view of an application of a method of manufacture of a vascular stent according to the present invention, in which a stent is partially expanded over a pre-formed mandrel to expose desired target support elements to a computer-controlled laser or other drilling or cutting device.

[016] FIG. 4 provides a side view of an application of a method of manufacture of a vascular stent according to the present invention using multiple lasers.

[017] FIG. 5 provides a side view of an alternate application of a method of manufacture of a vascular stent according to the present invention, in which a stent is bent in a pre- determined manner to expose desired target support elements to a computer-controlled laser or other drilling or cutting device.

MODES FOR CARRYING OUT THE INVENTION

[018] The present invention may be understood more readily by reference to the following detailed description of the preferred embodiments of the invention and the Examples included herein. However, before the preferred embodiments of the devices and methods according to the present invention are disclosed and described, it is to be understood that this invention is not limited to the exemplary embodiments described within this disclosure, and the numerous modifications and variations therein that will be apparent to those skilled in the art remain within the scope of the invention disclosed herein. It is also to be understood that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to be limiting.

[019] Unless otherwise noted, the terms used herein are to be understood according to conventional usage by those of ordinary skill in the relevant art. In addition to the definitions of terms provided below, it is to be understood that as used in the specification and in the claims, "a" or "an" can mean one or more, depending upon the context in which it is used.

[020] In an exemplary embodiment according to the present invention, a method is provided to fenestrate an endovascular stent comprised of circumferential or helically wound support elements, in a manner predetermined and designed to aid in the insertion of a rail or other longitudinal element through said fenestration, where said method comprises the steps of: (a.) aligning an unfinished endovascular stent over a mandrel of desired size and shape, such that at least a portion of said mandrel causes at least part of said stent to be at least partially expanded in the radial and/or longitudinal dimensions of said stent to expose at least the portion of the support element to be fenestrated; (b) fenestrating said exposed portion of said support element using a laser of appropriate wavelength and power to drill, cut, or otherwise fenestrate the support element in a manner and according to a predetermined pattern and controlled by a microprocessor and software; and (c) advancing the stent segmentally across the mandrel and repeating the fenestration process on successive support elements until all desired fenestrations have been accomplished.

[021] An endovascular stent suitable for fenestration according to the process of the present invention may be an elongated structure with a radial axis and a longitudinal axis, further defined by circumferential or helically wound support elements, and a stent lumen defined by and at least partially enclosed by said support elements. A stent suitable for fenestration according to the present invention may also have bridge elements joining adjacent support elements.

[022] Referring now to the drawings, in which like numerals indicate like elements throughout the several views, one embodiment of an exemplary endovascular stent amenable to manufacture using fenestration methods according to the method of the present invention is shown in its expanded condition in FIG. 1. As shown in FIG. 1, an exemplary endovascular stent 100 is an elongated tubular structure with support elements 4 which define and at least partially enclose a stent lumen 6 (not visible in FIG. 1), said stent having both a longitudinal axis 5 and a radial axis 10 (not visible in FIG. 1), fenestrations 9 (not visible in FIG. 1), longitudinal rails 7, and bridge elements 8 joining said support elements 4. Such an endovascular stent according to the present invention may be fabricated of biocompatible metals, metal alloys, or biocompatible polymers, which may be either be non-absorbable or absorbable.

[023] Shown in FIG. 2 is an isolated support element 4 of the stent shown in FIG. 1 in its unexpanded condition which more clearly show the stent lumen 6, radial axis 10, fenestrations 9, and bridge element 8. For purposes of clarity, the longitudinal rails 7 are not shown in FIG. 2.

[024] An embodiment of a method of fenestrating an endovascular stent according to the present invention is shown in FIG. 3, wherein an endovascular stent 100 as described and shown in FIG. 1 and FIG. 2 is advanced along its longitudinal axis 5 on a mandrel 15, said mandrel 15 ^"being shapecTtό at least partially expand said stent in its radial axis 10 as said stent 100 is advanced over said mandrel 15. As the stent 100 advances over the mandrel 15 and is expanded, target focus 30 on an individual support element 4, is exposed and aligned with a laser emitter 22 on a laser source 20 of suitable wavelength and power to fenestrate the support element 4. Upon alignment, the laser source 20 emits a laser beam 25 through the emitter 22 and fenestrates the support element 4. In this embodiment of the present invention, the laser source 20, may be under the control of a microprocessor-based control unit 30.

[025] According to the process of the present invention, the exemplary stent 100 is advanced over said mandrel 15 in sequential segments, or in a plurality of sequential segments, allowing cumulative fenestration of the entire desired area of said stent 100. Moreover, in an exemplary process according to the present invention, fenestration of multiple sides of said stent 100 may also be achieved, through rotation of the stent 100 on the mandrel 15, rotation of the mandrel 15 containing the stent 100, and/or rotation of the laser emitter 22 about the longitudinal axis 5..

[026] In another embodiment of the present invention, shown in FIG. 4, multiple (in this example 2) fenestrations 9 on the same support element can be created without rotating the stent 100 or emitter 22, through the use of multiple laser emitters 22 and beams 25. In this embodiment the fenestrations 9 can be created either through simultaneous or sequential emission of the laser beams 25.

[027] An alternate embodiment of a method of fenestrating an endovascular stent according to the present invention is shown in FIG. 5, wherein an endovascular stent 100 as described in FIG. 1 and FIG. 2 is introduced into a supporting rod mandrel 16 tlexed or bent at a predetermined location and angle, sufficient to expose a desired target focus 30 on a support element 4 to fenestration by a laser beam 25 emanating from an emitter 22 on laser source 20 of suitable wavelength and power to fenestrate the support element 4. In this embodiment of the present invention, the laser source 20, may be under the control of a microprocessor-based control unit 30.

[028] According to the process of the present invention, the exemplary stent 100 is advanced over said support rod 16 in sequential segments, or in a plurality of sequential segments, allowing cumulative fenestration of the entire desired area of said stent 100. Moreover, in an exemplary process according to the present invention, fenestration of multiple sides of said stent 100 may also be achieved, through rotation of the stent 100 on the mandrel 15, rotation of the mandrel 15 containing the stent 100, and/or rotation of the laser emitter 22 about the longitudinal axis 5.

[029] The flexing or bending of the stent is selected to direct and achieve the fenestration at a chosen angle and location. In such an embodiment according to the present invention, a stent may be bent, flexed, twisted, coiled, or otherwise manipulated during fabrication to provide an expanded area for laser or mechanical fenestration as previously described without requiring partial or complete expansion of the stent

[030] In an embodiment according to the present invention, fenestrations are achieved along an endovascular stent is appropriate locations to allow said fenestrations to receive a longitudinal rail therewithin throughout at least some of the length of said stent. In various embodiments of a process according to the present invention, the stent may receive fenestrations to allow placement of one or more longitudinal rails or wires therewithin. [031] An exemplary embodiment according to the method of the present invention, such as that shown in FIGS. 3 - 5, the desired fenestration may be achieved by a variety of methods including but not limited to machining, EDM, mechanical drilling, microassembly and laser cutting techniques. It should also be observed that using the embodiments shown in FIGS. 3 - 5, a stent of virtually unlimited length can be fenestrated without any loss of precision in the placement of fenestrations. Moreover, although the embodiments shown in FIGS. 3 - 5 illustrate the fenestration methods of the present invention on a stent comprised of circumferential support elements, the same methods can be applied to stents having helically wound support elements without significant departure from the spirit of the invention as broadly disclosed.

[032] It is contemplated that the various elements and methods according to the present invention can be combined with each other to provide the desired flexibility. For example, support element designs can be altered and various support element designs combined into a single stent with/without any one of the above-discussed wall elements. Similarly, the number, shape, composition and spacing of the stent wall elements can be altered to provide the stent with different properties. Additionally, the device can have varying numbers and placement of the bridge elements. The properties of any individual stent would be a function of the design, composition and spacing of the hoops, wall elements and bridges.

[033] The methods according to the present invention may be combined with other known and novel techniques to wholly manufacture an endovascular stent, starting with a tube of the metal or other material, and employing the techniques described above according to the present Invention to cut the desired pattern of stent elements in the support elements, obviating or reducing the need for subsequent assembly of individual stent elements.

[034] In addition, the methods according to the present invention may be used with a stent fabricated as disclosed herein, or by conventional manufacturing methods to further fenestrate the stent wall elements in a desired manner, and with precise fenestra location and sizing.

[035] The support elements, rails, bridges and other elements in a stent fenestrated according to the present invention may be fabricated from a variety of biocompatible materials, including, but not limited to, metals, alloys, and metallic compounds (e.g., metal oxides), polymers (e.g., resins), amorphous materials (e.g., ceramics, silica, and glassine), carbons (e.g., pyrolytic carbon, such as the coating Carbofilm™, amorphous carbon, activated carbon, and fullerenes as described, e.g., in WO 01/68158) and others. In general, suitable materials will exhibit biocompatibility, sufficient flexibility to navigate lumens during insertion, and the ability to contact and be secured relative to the vascular lumen wall. Any of the biocompatible materials may be used as the primary material to form the rails or other portions of the stents, or may be used to form a film, coating, or layer to cover a base material (e.g., a metal) that may or may not be biocompatible. Coating techniques are known in the art and are described, e.g., in U.S. Patent No. 6,153,252. If the stent material covers a base material that is itself biocompatible, complete coating of all exposed surfaces of the base material may not be necessary.

[036] Additional biocompatible metals and alloys include those disclosed, e.g., in U.S. Patent Nos. 4,733,665; 4,800,882; 4,886,062; and 6,478,815. Such metals an alloys include, but are not limited to, silver, tantalum, stainless steel, annealed steel, gold, copper alloys, cobalt alloys (e.g., cobalt-chromium-nickel alloys), titanium, tungsten, zirconium, niobium, iridium, and platinum. Shaped-memory metal alloys (e.g., Nitinol, a super elastic titanium alloy) may also be used to form the rails and/or stent wall elements discussed herein.

[037] Biocompatible polymers that are used with the rails and/or stent wall elements of the stents may be nonbioabsorbable, bioabsorbable in part, or substantially completely bioabsorbable.

[038] Finally, while there have been shown and described and pointed out fundamental novel features of the present invention as applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, and in the method illustrated and described, may be made by those skilled in the art without departing from the spirit of the invention as broadly disclosed herein. All of the above-discussed patents and publications are hereby expressly incorporated by reference as if they were written directly herein.

Claims

CLAIMSWE CLAIM:

1. A method for fenestrating the support elements of a tubular endovascular stent, comprising the steps of: a. introducing said stent having a longitudinal axis and a radial axis over a mandrel of desired shape and size; b. advancing said stent over said mandrel on a path parallel to said longitudinal axis to expand along said radial axis at least one of said support elements of said stent to expose a focus area on said support element; c. directing a fenestrating implement to engage said expanded support element at said focus area; d. fenestrating said expanded support element at said focus area using said fenestrating implement; and e. repeating steps (b), (c) and (d) until fenestrations have been created along at least a portion and extent of said stent.

2. The method of claim 1 wherein said fenestrating implement is a laser beam.

3. The method of claim 1 wherein said fenestrating implement is an electrical discharge machining tool.

4. The method of claim 1 wherein said fenestrating implement is a mechanical drilling tool.

5. The ^'method^"' of ^"claim 1 wherein said fenestrating implement is a microassembly tool.

6. The method of claim 1 wherein said support elements comprise circumferential hoops.

7. The method of claim 1 wherein said support elements comprise a continuous helically wound element.

8. A method for fenestrating the support elements of a tubular endovascular stent, comprising the steps of: a. introducing said stent having a longitudinal axis and a radial axis over a mandrel of desired shape and size; b. advancing said stent over said mandrel on a path parallel to said longitudinal axis to expand along said radial axis at least one of said support elements of said stent to expose a first focus area on said^'support element; c. directing a fenestrating implement to engage said expanded support element at said first focus area; d. fenestrating said expanded support element at said focus area using said fenestrating implement; e. rotating said stent about said longitudinal axis until a second focus area on said support element is exposed; f. directing a fenestrating implement to engage said expanded support element at said second focus area; g. fenestrating said expanded support element at said second focus area using said fenestrating implement; h. repeating steps (b), (c), (d), (e), (f) and (g) until fenestrations have been created along at least a portion and extent of said stent.

9. The method of claim 8 further comprising after step (g) the step of repeating steps (e), (f) and (g) to fenestrate said support element at additional focus areas.

10. The method of claim 9 wherein said fenestrating implement is a laser beam.

11. The method of claim 9 wherein said fenestrating implement is an electrical discharge machining tool.

12. The method of claim 9 wherein said fenestrating implement is a mechanical drilling tool.

13. The method of claim 9 wherein said fenestrating implement is a microassembly tool.

14. The method of claim 9 wherein said support elements comprise circumferential hoops.

15. The method of claim 9 wherein said support elements comprise a continuous helically wound element.

16. A method for fenestrating the support elements of a tubular endovascular stent, comprising the steps of: a. introducing said stent having a longitudinal axis and a radial axis over a mandrel of desired shape and size; T^T v anting^" said stent over said mandrel on a path parallel to said longitudinal axis to expand along said radial axis at least one of said support elements of said stent to expose a plurality of focus areas on said support element; c. directing a plurality of fenestrating implement to engage said expanded support element at said plurality of focus areas; d. fenestrating said expanded support element at said plurality of focus areas using said plurality of fenestrating implements; and e. repeating steps (b), (c) and (d) until fenestrations have been created along at least a portion and extent of said stent.

17. The method of claim 16 wherein said fenestrating implements are selected from the group of fenestrating implements comprised of: laser beams, electrical discharge machining tools, mechanical drilling tool, microassembly tools and combinations thereof.

18. The method of claim 16 wherein said fenestrating implement is a microassembly tool.

19. The method of claim 16 wherein said support elements comprise circumferential hoops.

20. The method of claim 16 wherein said support elements comprise a continuous helically wound element.

21. A method for fenestrating the support elements of a tubular endovascular stent, comprising the steps of: a! Introducing ^"a portion of said stent having a longitudinal axis and a radial axis over a support rod of desired shape and size; b. bending the un-introduced portion of said stent to expose a focus area on one of said support elements; c. directing a fenestrating implement to engage said exposed support element at said focus area; d. fenestrating said expanded support element at said focus area using said fenestrating implement; e. advancing said stent over said mandrel on a path parallel to said longitudinal axis to bend an additional one of said support elements; and f. repeating steps (c), (d) and (e) until fenestrations have been created along at least a portion and extent of said stent.

22. The method of claim 21 wherein said fenestrating implement is a laser beam.

23. The method of claim 21 wherein said fenestrating implement is an electrical discharge machining tool.

24. The method of claim 21 wherein said fenestrating implement is a mechanical drilling tool.

25. The method of claim 21 wherein said fenestrating implement is a microassembly tool.

26. The method of claim 21 wherein said support elements comprise circumferential hoops.

27.'Tne ^"method^" o^'t ^"claim 21 wherein said support elements comprise a continuous helically wound element.

28. A method for fenestrating the support elements of a tubular endovascular stent, comprising the steps of: a. Introducing a portion of said stent having a longitudinal axis and a radial axis over a support rod of desired shape and size; b. bending the un-introduced portion of said stent to expose a focus area on one of said support elements; c. directing a fenestrating implement to engage said exposed support element at said focus area; d. fenestrating said expanded support element at said focus area using said fenestrating implement; e. rotating said stent about said longitudinal axis until a second focus area on said support element is exposed; f. directing a fenestrating implement to engage said expanded support element at said second focus area; g. fenestrating said expanded support element at said second focus area using said fenestrating implement; h. advancing said stent over said mandrel on a path parallel to said longitudinal axis to bend an additional one of said support elements; and i. repeating steps (c), (d), (e), (f), (g) and (h) until fenestrations have been created along at least a portion and extent of said stent.

29. The method of claim 28 further comprising after step (g) the step of repeating steps (e), (f) and (g) to fenestrate said support element at additional focus areas.

30. ^'rTe ^"method^"' ol claim 29 wherein said fenestrating implement is a laser beam.

31. The method of claim 29 wherein said fenestrating implement is an electrical discharge machining tool.

32. The method of claim 29 wherein said fenestrating implement is a mechanical drilling tool.

33. The method of claim 29 wherein said fenestrating implement is a microassembly tool.

34. The method of claim 29 wherein said support elements comprise circumferential hoops.

35. The method of claim 29 wherein said support elements comprise a continuous helically wound element.