CA2216522A1

CA2216522A1 - Expandable surgical stent

Info

Publication number: CA2216522A1
Application number: CA 2216522
Authority: CA
Inventors: Anthony James Grass; Mohan Adiseshiah
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-03-21
Filing date: 1996-03-21
Publication date: 1996-09-26
Also published as: AU5116896A; GB9505721D0; EP0817599A1; WO1996029028A1; AU722946B2

Abstract

An expandable stent for a tubular (e.g. vascular) graft or prosthesis or for expanding or supporting a body passageway comprises a thin walled tubular member (102) having slots (104) defining a plurality of interconnected elongate members (108) arranged such that the application of a distributed radially-outward force within the tubular member expands it radially by deformation thereof, so as to open-out the slots, characterised by means (106, 107) defining relatively weak portions (118) of locally-reduced cross section which upon expansion of the stent act as plastic hinges and in which said deformation is concentrated.

Description

~VO 96129028 ~ JV~ O(~676 EXPANDABLE SURGICAL STENT

This invention relates to e~cpandable surgical stents for use ~ith vascular grafts or protheses or for the expansion and/or support of a blood vessel or other bodv passageway.
The surgical process of e~pandable imraluminal vascular grafting in~olves the insertion of a vascular graft into a blood vessel. The graft is in the form of a fabric tube eg. of TEFLON''D or DACRON~ having attached thereto an e~pandable stent enabling it to be attached to a healthy portion of blood vessel. The graft is manoeuvred using a balloon catheter to the desired position in the vesseL where the stent is expanded outwardly by infl~ting the balloon to abut the inner surface of the vessel, thereby holding the graft in place.
This procedure is common for example in the tre~tm~, t of blocked arteries, where, after opening the artery, the walls of the artery require internal support to prevent collapse; for the treatment of ~ortic and other aneurysms; and for the supportive reinforcement of constricted portions of the oesophagus. intestine and ureter, or other hollow viscera.
Such stents may take a variety of different forms~ such as helicallv wound coils. and e~cpandable structures of wires or bars. A known surgical stent is disclosed in EP-A-0 ~21 570, and is shown in Figure I hereof. The stent 70 comprises a thin-walled tube 71 in which a pluralit,v of slots 82 are formed. The slots 82 are of uniform length and are arranged both parallel to the longitudinal a~is of the tubular member 71 and circumferentiall-, thereb,v forming elongate members 75 in the wall 7~ of the tubular member 71. Each slot has ends bounded by members 77~ which connect adjacent elongate members 7~.
The Iube 71 has a first diameter d that permits the stent 70 to be inserted into the blood vessel or body passage. When in positiom the stent 70 mav be e~p~ntle~ by appl-ing CA 02216~22 1997-09-2~
WO 96ngo28 PCI~/GB96/00676 a radially outward force to the walls of the stent. This is achieved by infl~ting a balloon portion of a catheter situated along the longitudinal axis of the stent. The stent e:cpands to a diameter d' so that the walls of the stent come into contact with the inner walls of the blood vessel. The increase in the diameter of the stent is ~leterminecl by controlling the volumetric expansion of the balloon portion of the catheter. Following the required inflation of the balloon, the balloon is deflated and the catheter removed. leaving the expanded stent in position.
A problem that has been encountered in using the above stents occurs when there is any variation in the cross-section of the elongate members 75 or connecting members 77.
Should a portion of one of such members have a enlarged cross-section, for example, it will be more resistant to bending (i.e. it will be stiffer), and so will undergo a smaller radial expansion than the rem~in~ler of the wall of the stent for a particular balloon pressure. Small m~nl-f~-tllring irregularities in the initial unexp~n(led geometry of the stent can therefore produce significant irregularities in the final exr~ncled form. compromising its effectiveness for purpose. Because the bending resict~n~e is proportional to the square of the member width, the effect of small imperfections is m~gnified. The stent can therefore dilate under internal balloon pressure in a haphazard and inconsistent manner. Such behaviour is surgically highly undesirable. It is therefore critical that the fabrication process for the prior art stents is such that the lattice of members 75. 77 are of very closely uniform cross-section.
This is both difficult and expensive.
It is an object of at least the preferred embo(liment~ of the present invention to provide an exl?~nfl~ble stent that offers consistent expansion characteristics. Ieading to greater control over the final e~p~nr~ef~ shape of the stent. and repeatability in production.

WO 96/29028 r~,l/~br 't00676 Accordingly, in one aspect the present invention provides an exp~n-i~ble stent for a tubular (eg. vascular) graft or prosthesis or for e~rr~n~ling or supporting a body passageway.
said stent comprising~ a thin walled tubular member having slots defining a plurality of interconnected elongate rnembers arranged such that the application of a distributed radially-outward force within the tubular member expands it radially by deforrnation thereof, so as to open-out the slots~ characterised by means defining relatively weak portions of locally-reduced cross section which upon expansion of the stent act as plaslic hinges and in which said deformation is concentra~ed.
Preferably, the relatively weak portions are at the ends of the elongate members.
The relatively weak portions are defined by relativelv enlarged regions of adjacen~
slots.
In another aspect the invention provides an eYp~ntl~kle stent for a tubular (eg.
vascular) graft or prosthesis or for e~cr~ntling or supporting a body passagewa-, said s~ent comprising a thin walled tubular member having therein a plurali~ of slots distributed circu;nferentially and longitudinally of said tube, characlerised in that at least some of the slots have at least one locally-enlarged region, said regions defining an array of relati~ely weak portions in said tubular member whereby, on expanding said stent. said portions act as plastic hinges.
Preferablv, at least some of the slots have a pair of separate locallv-enlarged regions~
each one of the pair being situated equidistant from the centre of the slot, for exarnple at the ends of the slots.
Advantageously, at least some of the slots have a further pair of locally enlarged regions, each locally enlarged region of said further pair being situated equidistant from the centre of the slot. Each of one pair of locally enlarged regions situated in one slot is wo g6ngo28 CA 02216~22 1997 - 09 - 2~ /~r~00676 preferably aligned axially of the stent with one of the further pair of locally enlarged regions ~itl~t~-l in a circumferentially adjacent slot.
A locally enlarged region may be formed by a round hole of diarneter greater than the width of the slot.
Preferably. the material between unenlarged regions of circumferentially adjacent slots remains substantially undeformed during expansion of the tubular member.
In both of the above aspects of the present invention~ the slots may be equally circumferentially spaced around the tube, and preferably in a sta~gered relationship. The slots may be formed by mechanical cutting or by electro-discharge machining.
Preferably, the plurality of slots each have a first and a second end and the first ends of alternate circumferentially spaced slots are contained within the same radial plane perpendicular to the lon~ in~1 axis of the tube.
In another aspect the invention provides a tubular graft or prosthesis comprising at least one stent as set forth above.
The invention will now be described with reference to the accompanying drawings in which:-Figure lA is a perspective view of an e~cp~n-l~hle intraluminal stent according to the prior art.
Figure I B is a perspective view of the stent according to Figure 1 A in expanded form.
Figure ~ is a plan view of the expandable intraluminal stent according to the present invention which. for greater clarity, does not show all of the slots formed in the wall of the tube. Such slots as are shown are in a plane development so that their relative positions can be seen.

WO 96ngo28 1~ /00676 Figure 3 is a cross-section perpendicular to the longitudinal axis of the stent according to the present invention.
Referring to Figure 2, stent 100 comprises a seamless tubular member 102. The member is preferably of uniforrn thickness, for example ~50 ~Lm thick, and may be forrned from medical grade stainless steel. for example 316L. When for use in repair of an aortic aneurysm the stent has a length of typically 40 to 50mm, and a diarneter of 5mm.
A plurality of slots 104 are provided within the member 102~ thereby forming a plurality of elongate members 108 in the tubular member 102 that are joined by interconnections 110. The slots may be formed by a variety of different conventional methods, such as mechanical or laser cutting, electro-discharge machining or electro-chemical m~rltining exposed edges being rounded or otherwise deburred and blunted to avoid pl~P ~ g a sharp edge which may injure or irritate body tissue during insertion or subsequent use. For example, for a stent 40mm long and 5mm in diameter, the length of each slot is preferably 9mm, and the width of the slot is preferably less than 700~Lm. The slots 104 are distributed both longitudinally and circumferentially of the tubular member. In this example.
the longitudinal spacing between the slots is 250 ~m. and the circumferential spacing between c~nt slots is such that there is an angular pitch of 15~ berween the centres of the slots~ as shown in Figure 3. Circumferentially spaced ~-1jacent slots may also be arranged in a staggered relationship, as shown in Figure 2 where, in this example, the ends of ~ltPrrl~t~o circurnferentially spaced slots are contained within the sarne radial plane perpendicular to the longit~l~lin~l axis of the tubular member.
First 106 and second 107 pairs of locally-enlarged regions are forrned in each of the slots 104, thereby forming portions of locally reduced cross-section 118 in the elongate members 108. This is the preferred arrangement, but the invention is not limited to this WO 96n9028 CA 0 2 2 16 ~ 2 2 19 9 7 - O 9 - 2 5 p~,-l /~.,3~:100676 particular number of locally-enlarged regions 106, 107. The locally-enlarged regions 106, 107 preferably take the form of round holes of diameter greater than the width of the slot and preferably at least twice as wide. For example, for a slot width of '~00 um or less. the diameter of the hole may be 400 !lm. In the preferred embodiment shown in Figure ~, each slot 104 contains two pairs of holes 106 and 107. The holes of each pair are situated equidistant from centre 116 of the slot. One pair, 107, is situated at the ends of the slots, whereas each of the other pair 106 is situated so as to be aligned axially of the stent with one of the pair of holes 107 in the circumferentially ~ cent slot. With this configuration, the cross-section of the portions 118 are subst~nti~lly reduced in comparison with the cross-section of material between unenlarged regions of the slots 104 of the stent. In this example, the width b of portion 118 is '~53~1m + 10~m, compared to a width of approximately 0.45mm for the major portion of the elongate memhers 108. For the stent to have consistent expansion characteristics, it is important that the dimension b is accurately controlled. Thus the positions and diameter of the holes 106,107 is subject to a close tolerance, but the width of the major part of the elongate members may be subject to a wider tolerance. In this example the holes are nominally 40011m ~ mettor, spaced lon~inl-iin~lly at 4.15mm centres and at 15~ intervals circumferentially .
In operation, the stent 100 is expanded by infl~ting a balloon portion of a catheter placed within the stent substantiallv along the longitudinal axis of the stent 100. When the balloon comes into contact with the inner walls of the stent, the balloon exerts a radially-outward force on the walls of the stent, causing the stent to radially expand by deformation so as to open-out the slots 104. Portions of the stent 118 having a reduced cross-section are relatively weak col~lpaled to the material between the unenlarged regions of the slots of the stent, and so are ~refe~e.-Lially deformed by the balloon. Due to the concentration of the WO 96r29028 1 ~1/~D~6/OU676 deformation in the portions 118, the material of the members 108 between unenlarged regions of the slots remains substantially undeformed by the force acting on them by the exF-~n-linf~
balloon. The portions 118 act as plastic hinges, permitting pivotal movement of the members 108 between the hinges as the diameter of the stent expands.
The relatively weal~ portions in the walls of the stent thus deterrnine the expansion characteristics of the stent and its final shape. The final shape of the stent of the invention is therefore much more controlled than the final shape of known stents not provided with defined points of w~kn~cc, thereby providing a significant improvement in the safety of vascular grafting or prostheses operations with the final shape of the stent. and its expansion behaviour, being much more concictPnt and reliable. The size and location of the holes 106, 107 may be reliably controlled and repeatable in production of the stents, to the necessary degree of accuracy using known techniques. Because the resulting cross section of the plastic hinges 118 is m~rk~rlly less than that of the members 108, the small tolerance which is required in forming the holes 106, 107 can be subst~nt~ v relaxed when forrning the connecting slots, thus easing ~e~n~n~1c on the m~nnf~cnlring process.
The stents may be made in a variety of sizes of both length and diameter, ~ith different stiffn~sses and ratios of expanded to unexpanded diarneter, depending on the intend~d use in each case. They may be used alone to expand and/or support occluded or weak blood vessels or other body passageways (hollow viscera) or may be used in combination with a tubular prosthesis or graft to anchor the ends of the prosthesis in healthy but spaced-apart portions of a duct (eg. the aorta) enabling an intervening weak or damaged portion of the duct to be bndged by the graft.

WO 96/29028 CA 0 2 2 16 5 2 2 19 9 7 - O 9 - 2 5 PCI~/GB96/00676 Each feature disclosed in this specification (which term includes the claims) andlor shown in the drawings may be incorporated in the invention independently of other disclosed and/or illustrated features. .

SUMM ~RY
An exr~n~ble stent for a tubular (eg. vascular) graft or prosthesis or for e~p~n-ling or supporting a body passageway comprises a thin walled tubular member ( 10 ) having slots (104) defining a plurality of hll~.col~ected elongate members (108) arranged such that the application of a distributed radially-outward force within the tubular member expands it radially by deformation thereof, so as to open-out the slots, characterised by means ( 106,107) rlefining relatively weak portions ( 1 18) of locally-reduced cross section which upon expansion of the stent act as plastic hinges and in which said deformation is concentrated.

Claims

1. An expandable stent for a tubular graft or prosthesis or for expanding or supporting a body passageway, said stent comprising a thin walled tubular member having slots defining a plurality of interconnected elongate members arranged such that the application of a distributed radially-outward force within the tubular member expands it radially by deformation thereof, so as to open-out the slots, characterised by means defining relatively weak portions of locally-reduced cross section which upon expansion of the stent act as plastic hinges and in which said deformation is concentrated.

2. A stent as claimed in claim 1, wherein the relatively weak portions are at the ends of the elongate members.

3. A stent as claimed in claim 1 or claim 2, wherein the relatively weak portions are defined by relatively enlarged regions of adjacent slots.

4. An expandable stent for a tubular graft or prosthesis or for expanding or supporting a body passageway, said stent comprising a thin walled tubular member having therein a plurality of slots distributed circumferentially and longitudinally of said tube, at least some of the slots having at least one locally-enlarged region, characterised in that said regions define an array of relatively weak portions in said tubular member whereby, on expanding said stent, said portions act as plastic hinges.

5. A stent as claimed in any preceding claim, wherein said slots are equally circumferentially spaced around the tube.

6. A stent as claimed in Claim 4 or Claim 5, wherein circumferentially spaced adjacent slots are arranged in a staggered relationship.

7. A stent as claimed in Claim 6, wherein the plurality of slots each have a first end and a second end and where the first ends of alternate circumferentially spaced slots are contained within the same radial plane perpendicular to the longitudinal axis of the tube.

8. A stent as claimed in Claim 4, wherein at least some of said slots have a pair of separate locally-enlarged regions, each one of said pair being situated equidistant from the centre of the slot.

9. A stent as claimed in Claim 8, wherein said pair of locally-enlarged regions are situated at the ends of the slots, 10. A stent as claimed in Claim 8 or Claim 9, wherein at least some of said slots have a further pair of locally-enlarged regions, each locally-enlarged region of said further pair being situated equidistant from the centre of the slot.

11. A stent as claimed in Claim 10, wherein each of one pair of locally-enlarged regions situated in one slot are aligned axially of the stent with one of the further pair of locally-enlarged regions situated in a circumferentially adjacent slot, 17. A stent as claimed in Claim 3 or Claim 4, wherein a said locally-enlarged region is formed by a round hole of diameter greater than the width of the slot.

13. A stent as claimed in any of the preceding claims, wherein said tubular member is of uniform wall thickness.

14. A stent as claimed in any of the preceding claims. wherein the slots are formed by mechanical cutting.

15. A stent as claimed in any one of Claims 1 to 12, wherein the slots are formed by electro-discharge machining.

16. A stent as claimed in Claim 4, wherein the material between unenlarged regions of circumferentially adjacent slots remains substantially undeformed during expansion of the tubular member.

17. A tubular graft or prosthesis including at least one stent as claimed in any preceding claim.