Vascular prosthesis

Abstract: The invention provides a prosthesis comprising a first stent and a second stent and stent joining means for joining two endoluminal stents one to the other to define a continuous lumen through the two stents, said stent joining means comprising: a male engaging portion (42) on said first stent which can be compressed radially inwardly; and a female cooperating portion (15) on said second stent; wherein the male engaging portion (42) can be entered into the female cooperating portion (18) in a radially compressed state and thereafter caused or allowed to expand in the female cooperating portion; the arrangement being such that in service the inter-engagement of the male engaging portion and the female cooperating portion so as to resist relative longitudinal movement of the two stents one from the other.

Description: The present invention relates to a stent assembly comprising stent joining means for joining two endoluminal stents one to the other to define a continuous lumen through the two endoluminal stents. An endoluminal stent is used to provide a prosthetic intraluminal wall e.g. in the case of a stenosis to provide an unobstructed conduit for blood in the area of the stenosis. An endoluminal prosthesis comprising a stent which carries a prosthetic graft layer of fabric is used e.g. to treat an aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of embolism, or of the natural artery wall bursting. Typically, a stent or endoluminal prosthesis is implanted in a blood vessel at the site of a stenosis or aneurysm by so-called "minimally invasive techniques" in which the stent is compressed radially inwards and is delivered by a catheter to the 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 When the stent is positioned at the correct location, the catheter is withdrawn and the stent is caused or allowed to re-expand to a predetermined diameter in the vessel. US-A-4733665 discloses an expandable intraluminal graft which is constituted by a tubular member formed from a plurality of intersecting elongate members which permit radial expansion and compression of the stent. US-A-5064435 discloses a body implantable stent consisting of two or more generally tubular co-axially and slidably connected stent segments. The stent is elastically deformed to a reduced radius when deployed, and when released after positioning, self-expands radially into contact with a tissue wall segment defining a blood vessel or other body cavity As each stent segment expands radially, it contracts in the axial direction. Such contraction is accommodated by a reduction in the length of medial regions where adjacent stent segments overlap; thus maintaining the overall length of the stent. Throughout this specification, the term "proximal" shall mean "nearest to the heart," and the term "distal" shall mean "furthest from the heart." According to the present invention there is provided a stent assembly as claimed in claim 1 below. Typically, the said other stent may include a proximal male engaging portion; and said one stent may include a distal female cooperating portion. The male engaging portion may be flared radially outwardly towards its extremity, and the female cooperating portion may be tapered radially inwardly towards its extremity. In some embodiments, the male engaging portion may comprise a frustoconical wall which flares outwardly towards its longitudinal extremity; the female cooperating portion may comprise a frustoconical wall which tapers radially inwardly towards its longitudinal extremity. Alternatively, said male engaging and female cooperating portions may be substantially untapered; they may be substantially cylindrical. The male engaging portion of the other stent may be resiliently compressible in a radially inwards direction such that in the radially compressed state it is capable of self-reexpansion to engage in the female cooperating portion. Typically, each of said stents may be resiliently compressible. In use therefore the one stent may be delivered in a radially compressed state by using a catheter; when the one stent is located at the site of use, the catheter may be withdrawn thereby allowing the one stent to re-expand to engage the endoluminal surface of the blood vessel. The other stent may then be delivered percutaneously or by a "cut down" technique to a site distal of the one stent such that the male engaging portion of the other stent in the radially compressed state is entered into the expanded female cooperating portion of the one stent; the catheter may then be withdrawn allowing the other stent to re-expand such that the male engaging portion engages in the female cooperating portion of the one stent. Typically, the proximal end of said one stent may be flared radially outwardly towards its extremity to engage the endoluminal surface of the artery thereby to resist longitudinal movement of the one stent in service. Each of the stents may comprise a sinuous wire formed into a tubular configuration. The sinuous and tubular configurations may be imparted to the wire by winding it on a mandrel. Typically, each stent may be made from a shape memory nitinol (nickel-titanium) wire which may be wound on to the mandrel to form the stent in a tubular configuration of slightly greater diameter than the diameter of the blood vessel in which the stent is intended to be used. The stent may be annealed at an elevated temperature and then allowed to cool in air so that the nitinol wire "remembers" the configuration in which it was wound on the mandrel. Said nitinol wire may be type "M" nitinol wire which is martensitic at temperatures below about 13°C and is austenitic at temperatures above about 25°C; it will be appreciated therefore that the type "M" wire will be austenitic at body temperature of 37°C. Typically, the annealing may be conducted at about 500°C or more for at least about 60 minutes; after cooling the wire may be immersed in cold water to facilitate removal of the wire from the mandrel with the wire in its maleable martensitic form. Typically, the cold water may have temperature of less than about 10°C; the wire may be immersed for about 5 minutes or more. An advantage of using nitinol wire to form the stent is that the nitinol wire is "super elastic" in its austenitic state; the radial outward force exerted by the stent on the wall of the blood vessel in use is therefore substantially constant irrespective of the diameter of the vessel and the expanded stent. In some embodiments the wire may have a helical configuration as disclosed in EP-A-0556850. Alternatively, the wire may be of a configuration in which the wire forms a plurality of hoops such that the plane of the circumference of each hoop is substantially perpendicular to the longitudinal axis of the stent. Each hoop may comprise a substantially complete turn of the wire having a sinuous configuration; optionally, as each hoop is completed, the point of winding the wire may be displaced longitudinally with respect to the winding axis to form the next hoop. When the next hoop is complete, the point of winding is moved further longitudinally with respect to the winding axis to form the next succeeding hoop and so on. It will be appreciated that an advantage of this arrangement is that the planes of the hoops are not skewed with respect to the longitudinal axis of the stent; the longitudinal ends of the stent are "square" to said longitudinal axis, so that when the stent is caused or allowed to expand in situ there is substantially no twisting of the stent as it shortens in length. It will be appreciated that this represents a significant advantage, as in areas of stenosis or aneurysm it is desirable to minimize the movement of the stent within the blood vessel so as to reduce the potential trauma to the patient. Typically, the stents whether of the helical or perpendicular variety, also comprise a securing means for securing an apex of the sinuous wire in one hoop to a juxtaposed apex of a neighboring hoop so that each hoop is supported by its neighbors. The securing means may comprise a loop element of a suture material, for example, to tie the juxtaposed apices together; the loop element may also comprise a loop formed of a thermoplastics material such, for example, as polypropylene. Alternatively, the securing means may be a bead formed of a thermoplastic material around juxtaposed apices. Also alternatively, the securing means may be a loop, ring, or staple formed of wire such as nitinol. The male engaging portion and female cooperating portion, of the interengaging stents of this invention, may be formed separately from the remainder of the respective non-engaging portions of these stents and then the engaging and non-engaging portions secured to one another by securing means. At least one of the stents of the stent assembly of the present invention may carry a tubular graft layer formed from a biocompatible fabric in juxtaposition with the stent; the combined stent and graft layer constituting an endoluminal prosthesis. Typically the graft layer may be disposed externally of the stent; it will be appreciated however that in some embodiments the graft layer may be disposed internally of the stent. In some embodiments the graft layer on the one or other stent may be secured to the stent by loop elements such, for example, as loops of polypropylene. The biocompatible fabric may be a polyester fabric or a polytetrafluoroethylene fabric; typically said fabric may be woven or a warp knitted polyester fabric. In some embodiments the woven or a warp knitted fabric may be formed in a seam-free bifurcated configuration as a sleeve for a bifurcated stent. In some embodiments the male engaging portion of the other stent and the female cooperating portion of the one stent may be left uncovered. Alternatively, the fabric graft layer may extend to the proximal extremity on the external surface of the male engaging portion, and may be folded over the distal extremity of the female cooperating portion to form an inner sleeve; in use the external fabric of the male engaging portion may butt against the folded over portion of the fabric internally of the female cooperating portion to form a substantially blood tight seal. It will be appreciated by a person skilled in the art that the prosthesis of the present invention may be introduced to the site of use percutaneously or by "cut down" techniques. Either of the stents of the prosthesis may be provided on its external surface with circumferentially spaced wire barbs or hooks adapted to engage in the endoluminal surface of the host artery to resist longitudinal movement or slippage of the stent in use. Typically the barbs or hooks may be disposed on part of the stent which is provided with a fabric graft layer such that in use the points of the artery which are engaged by the barbs or hooks are covered by the fabric graft. It will be appreciated by a person skilled in the art that the trauma to the artery wall caused by the hooks or barbs may cause emboli; the provision of the fabric graft over the barbs or hooks in use will therefore help to prevent the introduction of such emboli into the blood stream. The male engaging portion for the other stent may be provided with circumferentially spaced hooks or barbs on its external surface to engage the internal surface of said female cooperating portion, thereby to reinforce the connecting means against longitudinal separation of the stents one from the other in the service. The present invention therefore provides a stent assembly comprising connecting means for connecting two stents longitudinally one to the other. It will be appreciated that this represents a significant step forward in the art as it allows the provision of a bifurcated endoluminal prosthesis for use in juxtaposition e.g. with arterial bifurcations without requiring by-pass surgery to connect one of the branched arteries to the other branched artery. In particular, the invention makes it possible to provide a bifurcated endoluminal prosthesis which can be positioned in an artery in juxtaposition with a bifurcation to extend into one of the branched arteries; the bifurcated prosthesis can be connected to another prosthesis which extends into the other branched artery. The prostheses can be delivered percutaneously or by "cut down" methods and connected together in situ thereby to provide effective treatment of an angeological disease such, for example, as an aneurysm or a stenosis which extends across a bifurcation in a blood vessel without the need for by-pass surgery. Following is a description by way of example only with reference to the accompanying drawings of embodiments of the present invention. In the drawings:- Figure 1a is a front view of a bifurcated intraluminal stent constituting part of an endoluminal prosthesis. Figure 1b is a front view of another stent which is adapted to be connected to the bifurcated stent of Figure 1a. Figure 2(a) is a side view of part of the bifurcated stent of Figure 1a opened up to show its construction. Figure 2(b) is a side view of an exemplary mandrel used to form the part of the bifurcated stent shown in Figure 2(a). Figure 3 is a side view of another part of the bifurcated stent of Figure 1a opened up to show its construction. Figure 4(a) is a side view of yet another part of the bifurcated stent of Figure 1a opened up to show its construction. Figures 4(b)-4(f) are partial exploded views of the exemplary stent of Figure 4(a) illustrating alternative means for securing juxtaposed apices according to the present invention. Figure 5 is a schematic perspective view of a bifurcated endoluminal prosthesis. Figure 6 is a schematic view of another bifurcated endoluminal prosthesis. Figure 7 is a schematic view of yet another bifurcated endoluminal prosthesis. A bifurcated stent which is indicated at 10 in Figure la comprises a wire skeleton which is constructed in four separate parts, namely a proximal part 12, a first frustoconical part 14, a first distal part 16 and a second frustoconical part 18 Said bifurcated stent 10 carries a fabric graft layer (Figures 5, 6, and 7) for use as an endoluminal prosthesis e.g. in the infrarenal portion of a mammalian aorta in juxtaposition with the bifurcation of the common iliac arteries. It will be appreciated, however, that bifurcated stents (with or without fabric graft layers) for use in different parts of the angeological system and for different mammals can be constructed by varying the dimensions of the stent accordingly. Examples of diseases that can be treated using the apparatus of the present invention include aneurysm, stenosis, and occlusion. Each of the four parts of the bifurcated stent 10 is made in substantially the same way by winding a shape memory nitinol wire, typically nitinol type M wire, onto a mandrel 46. The construction of the exemplary proximal part 12 of the bifurcated stent 10 is shown in Figures 2(a) and 2(b); nitinol wire type M wire typically having a diameter of 0.46mm (0.018") is wound around mandrel 46 to form a plurality of hoops 20. The winding surface of mandrel 46 is provided with a plurality of upstanding pins 47 disposed in a zig-zag pattern for each of the hoops 20 so that in each hoop 20 the nitinol wire follows a sinuous path to define a plurality of circumferentially spaced apices 22. Each hoop 20 is wound onto mandrel 46 such that the plane of the circumference of each hoop 20 is substantially perpendicular to the longitudinal axis of the mandrel. When one hoop 20 e.g. the hoop indicated at 20a has been formed, the point of winding of the nitinol wire is displaced longitudinally with respect to the axis of mandrel 46 to form the next successive hoop 20b The stent shown in Figure 2(a) is the stent formed on mandrel 46 shown in Figure 2(b) after cutting the stent longitudinally and rotating it 45 degrees to show the construction of the stent. The proximal part of the bifurcated stent of Figure 1a is formed on the mandrel with a diameter of about 24mm and a length in the longitudinal direction of about 55mm. From Figures 1(a), 2(a), and 2(b) it will be noted that the proximal part 12 is constituted by three hoops 20 of unit width at the proximal end 24 of the proximal part 12, two intermediate hoops 25 of twice unit width and, at its distal end 26, by a single hoop 20 of unit width. In the illustrated embodiment, intermediate hoops 25 have a plurality of offsets 25a. Offsets 25a are formed when the wire is passed around pins 47 on mandrel 46. Offsets 25a add stability to the stent. When the nitinol wire has been wound onto mandrel 46, the nitinol wire is annealed at an elevated temperature and then allowed to cool. The wire is annealed at a temperature of about 500°C for 60 minutes and is then allowed to cool in air. The purpose of the annealing is so that the nitinol wire in its austenitic form "remembers" its configuration as wound on mandrel 46; it will be appreciated therefore that other temperatures and durations for the annealing are included within the present invention provided the nitinol wire "remembers" its wound configuration. After annealing and cooling, the wire is immersed in cold water at less than 10°C for about 5 minutes; the wire is then removed from the mandrel, and juxtaposed apices 22 of neighboring hoops 20 are secured together by securing means 99 (see Figure 4(a)), which are, in this example, 0.003" polypropylene filaments. Each apex 22 of each hoop 20 which has a juxtaposed apex of a neighboring hoop 20 is tied to the juxtaposed apex 22. It will be appreciated, however, that alternatively only some of the juxtaposed apices 22 may be secured in this way. In addition to polypropylene filaments, the securing means may comprise a loop element 99a of a suture material, for example, to tie the juxtaposed apices together, as shown in Figure 4(b). The securing means may also comprise bead 99b formed of a thermoplastic material around juxtaposed apices, as shown in Figure 4(c). Also alternatively, the securing means may be a loop 99c, ring 99d, or staple 99e formed of wire such as nitinol, as shown in Figures 4(d), 4(e), and 4(f) respectively. The first and second frustoconical parts 14, 18 of the skeleton shown in the figures are formed in substantially the same way as the proximal part 12 by winding nitinol wire onto a mandrel and then annealing the wire before removing it from the mandrel. As shown in Figure 3, the first and second frustoconical parts 14, 18 are each constituted by three hoops 20 of unit width. The mandrel is tapered such that the proximal end of each of the frustoconical parts 14, 18 is formed with a diameter of about 12mm and the distal end 32 of each is formed with a diameter of about 9mm. The overall length of each of the exemplary frustoconical parts 14, 18 is about 18mm. The wire used for the frustoconical parts 14, 18 is nitinol type M wire having a diameter of 0.28mm (0.011"). Juxtaposed apices 22 of each of the frustoconical parts 14, 18 are tied together using 0.03" polypropylene filaments as described above. The first and second frustoconical parts 14, 18 are secured to the distal end 26 of the proximal part 12 of the stent 10 in transversely spaced relation as shown in Figure la by securing the apices 22 of the hoop 20 forming the wider proximal end 30 of each of the frustoconical parts 14, 18 to juxtaposed apices 22 of the hoop 20 on the distal end 26 of the proximal part 12. The first distal part 16 of the bifurcated stent 10 is formed by winding nitinol type M wire typically having a diameter of 0.28mm (0.011") onto a mandrel to form twelve longitudinally spaced hoops 20 as shown in Figure 4; the first distal part has an overall length of about 66mm and a uniform diameter of about 9mm. The proximal end 34 of the distal part 16 is secured to the narrower distal end 32 of the first frustoconical part 14 by tying each apex 22 on the proximal end 34 of the first distal part 16 to a juxtaposed apex on the distal end 32 of the first frustoconical part 14 using, in this embodiment, 0.003" polypropylene filaments. The proximal part 12, the first and second frustoconical parts 14, 18, and the first distal part 16 are each covered with a tubular graft layer of a biocompatible woven fabric such, for example, as a plain woven fabric made from 30 or 40 denier polyester. The tubular fabric layers may be attached to the proximal and distal parts 12, 16 of the stent 10 by stitching with, for example, 0.003" polypropylene filaments around the apices 22 of the underlying skeleton. The proximal part 12 of the wire skeleton may be provided with a plurality of circumferentially spaced hooks or barbs 43 which project through the tubular fabric layer to engage in the endoluminal surface of a host artery in service. The sinuous configuration of each turn 20 of the wire skeleton of the stent 10 allows the prosthesis to be compressed resiliently radially inwards so that it can be received in a catheter e.g. a 16 or 18 French catheter for percutaneous or cut down delivery, e.g. to an intraluminal site in the infrarenal section of the aortic artery. Larger diameter catheters up to, e.g., 20 French, may be used to deliver the prosthesis using "cut down" procedures. An x-ray opaque marker may be attached to one or more ends of a stent so that the delivery of the stent can be monitored using x-rays. As shown in Figure 4(a), such a radiopaque marker may typically comprise a gold or platinum wire 17 crimped onto an end of stent 16. Alternatively, the radiopaque marker may be a tube 17a disposed around a length of wire on the stent, also as shown in Figure 4(a). Typically, in the bifurcated stent the marker is secured to the stent in line with the distal stent portion so that the distal stent portion can be aligned with and inserted into one of the branched arteries in situ. The bifurcated endoprosthesis is positioned in the infrarenal section of the aortic artery in juxtaposition with the bifurcation of the common iliac arteries such that the first distal part 16 of the prosthesis extends into one of the common iliac arteries. The catheter is then withdrawn allowing the stent 10 to re-expand towards its configuration as wound on the mandrel in which it was annealed until the stent engages the endoluminal surface of the host artery. The barbs or hooks engage the endoluminal surface of the host artery to resist longitudinal displacement or slipping of the prosthesis in use. It will be appreciated that when the bifurcated prosthesis is positioned and re-expanded in the fitted position, blood can flow from the aortic artery into the proximal part 12 of the prosthesis from where it can flow into the one common iliac artery through the frustoconical part 14 and the first distal part 16 and also into the other common iliac artery through the second frustoconical part 18. In order to implant a prosthesis in the other common iliac artery a second prosthesis comprising a second stent 40 as shown in Figure 1b is used. The second stent 40 includes a wire skeleton comprising a proximal frustoconical part 42 and a distal part 44. The distal part 44 of the second stent 40 also may be covered with a tubular graft layer of a biocompatible fabric such, for example, as polyester or polytetrafluoroethylene fabric. The frustoconical proximal part 42 is constructed in the same way as the frustoconical parts 14, 18 of the bifurcated stent 10; the distal part 44 is constructed in the same way as the distal part 16 of the bifurcated stent 10. The distal end of the frustoconical proximal part 42 is secured to the proximal end of the distal part 44 by securing juxtaposed apices using polypropylene filaments as described above. In use, the second prosthesis is compressed radially inwards and is received in a catheter for percutaneous or "cut down" delivery to the other common iliac artery. The frustoconical proximal part 42 is guided, in the radially compressed state, into the second frustoconical part 18 of the bifurcated stent 10. The catheter is then withdrawn allowing the second stent 40 to re-expand towards its remembered configuration, until the distal part 44 engages the endoluminal surface of the other common iliac artery, and the outer surface of the frustoconical proximal part 42 engages the interior surface of the second frustoconical part 18 of the bifurcated stent 10. Again, radiopaque markers may be used to align distal portion 44 properly with proximal portion 12. As with other stents described herein, the frustoconical proximal part 42 may be formed with circumferentially spaced barbs or hooks 43, as shown in Figure 1b, which engage in the wire skeleton of the second frustoconical part 18 of the bifurcated stent 10. When barbs 43 are on proximal portion 12, they engage the inner wall of the artery. The tapered configurations of the second frustoconical part 18 of the bifurcated stent 10 and of the proximal frustoconical part 42 of the second stent 40 are such that in the fitted position as described, the stents are locked together to resist longitudinal separation in service. Barbs or hooks on the second stent 40 and/or on frustoconical proximal part 42 help to resist such longitudinal separation. Another bifurcated endoluminal prosthesis 50 as shown in Figure 5 includes a bifurcated stent comprising a proximal portion 52 which tapers radially inwardly from its proximal end 54 to its distal end 56, and first and second transversely spaced frustoconical distal portions 58, 60 which are secured to the distal end 56 of the proximal portion 52; the proximal portion 52 is covered with a tubular graft layer of a biocompatible fabric 62. In use the prosthesis is delivered percutaneously or by "cut down" methods to an artery in juxtaposition with an arterial bifurcation; blood can flow through the frustoconical proximal portion 52 into each of the branched arteries through the first and second distal frustoconical portions 58, 60. In order to provide a prosthesis in one or both of the branched arteries, a separate prosthesis comprising a stent of the type shown in Figure 1b referred to above covered with fabric is connected to the bifurcated prosthesis 50 by inserting and re-expanding the proximal end of such a separate prosthesis in one or both of the distal frustoconical portions 58, 60 of the prosthesis 50 for engagement therein. Another variant of the present invention is shown in Figure 6 which shows a bifurcated endoluminal prosthesis 70 having a proximal portion 72 which is secured at its distal end 74 to two transversely spaced frustoconical intermediate portions 76, 78. One of said frustoconical intermediate portions 76 is secured at its distal end to an elongate distal portion 80. The proximal end 82 of the proximal portion 72 is flared radially outwards towards its proximal end 82 to engage the intraluminal surface of the host blood vessel in service. Save for this flared portion, the entire endoprosthesis is covered with a fabric graft layer as shown in Figure 6, said graft layer is carried externally of the wire skeleton and is folded over the distal extremity 84 of the other frustoconical intermediate portion 78 to form an internal lining in said other frustoconical intermediate portion 78. Said other frustoconical intermediate portion 78 constitutes a female cooperating portion in accordance with the present invention which is adapted to receive a male engaging portion of another prosthesis as indicated at 86 in Figure 6. Said other prosthesis 86 includes a frustoconical proximal portion 88 which constitutes the male engaging portion and an elongate distal portion 90. The whole of the other prosthesis 86 is covered with a fabric graft layer as shown in Figure 6. In service, the male engaging portion 88 of the other prosthesis 86 is entered into and engaged with the female cooperating portion 78 of the bifurcated prosthesis 70 in situ in the manner herein before described. The fabric layer on the male engaging portion 88 butts face-to-face on the folded over portion of the fabric layer disposed internally of the female cooperating portion 78 to form a substantially blood-tight seal therewith. Yet another variant of the present invention is shown in Figure 7 in which a bifurcated endoluminal prosthesis 91 has a generally cylindrical proximal portion 92; said proximal portion 92 is connected at its distal end 93 to an elongate, generally cylindrical distal portion 94. Said proximal portion 92 is also connected at its distal end 93 to a generally cylindrical intermediate portion 95 which is secured in transversely spaced relation to the elongate distal portion 94 Said cylindrical intermediate portion 95 constitutes a female cooperating portion which is adapted to receive a generally cylindrical male engaging portion of a second elongate prosthesis (not shown). The male engaging portion is equipped with circumferentially spaced external barbs to engage in the female cooperating portion in service. As shown in Figure 7, the whole of the bifurcated prosthesis 91 is covered with an external fabric graft layer save for a flared portion 96 towards the proximal end 97 of the proximal portion 92.

Claims: A stent assembly comprising two endoluminal stents and stent joining means for joining the two endoluminal stents one to the other to define a continuous lumen through the two endoluminal stents, wherein said stent joining means comprises a female cooperating portion (18;78;95) on one of said endoluminal stents and a male engaging portion (42;88), which can be compressed radially inwardly, on the other of said endoluminal stents, characterised in that: said male engaging portion is configured to be deployed and engaged with said female cooperating portion subsequent to deployment of said female cooperating portion; wherein the male engaging portion (42;88) can be entered into the female cooperating portion (18;78;95) in a radially compressed state and thereafter caused or allowed to expand in the female cooperating portion; the arrangement being such that the male engaging portion and the female cooperating portion are thereby interengaged to resist longitudinal movement to prevent separation of the two endoluminal stents one from the other in service. A stent assembly as claimed in claim 1 wherein said other stent includes a proximal male engaging portion. A stent assembly as claimed in claim 1 or claim 2 wherein said one stent includes a distal female cooperating portion. A stent assembly as claimed in claim 1, claim 2 or claim 3 wherein said male engaging portion is flared radially outwardly towards its extremity. A stent assembly as claimed in any preceding claim wherein the male engaging portion comprises a frustoconical wall which flares outwardly towards its longitudinal extremity. A stent assembly as claimed in any preceding claim wherein the female engaging portion comprises a frustoconical wall which tapers radially inwardly towards its longitudinal extremity. A stent assembly as claimed in claim 1, claim 2 or claim 3 wherein said male engaging portion and said female cooperating portion are substantially untapered. A stent assembly as claimed in claim 1, claim 2, claim 3 or claim 7 wherein said male engaging portion and said female cooperating portion are substantially cylindrical. A stent assembly as claimed in any preceding claim wherein said male engaging portion is resiliently compressible in a radially inwards direction such that in a radially compressed state the male engaging portion is capable of self re-expansion to engage in the female cooperating portion. A stent assembly as claimed in any preceding claim wherein each of said stents is resiliently compressible. A stent assembly as claimed in any preceding claim wherein the proximal end of said one stent is flared radially outwardly towards its extremity to engage the endoluminal surface of the blood vessel thereby to resist longitudinal movement of the one stent in service. A stent assembly as claimed in any preceding claim wherein each of said stents comprises a sinuous wire formed into a tubular configuration. A stent assembly as claimed in any preceding claim wherein each of said stents is formed from a shape memory nitinol (nickel/titanium) wire. A stent assembly as claimed in claim 12 or 13 wherein said each of the wires 5 forming said stents defines a plurality of hoops (20) such that the plane of the circumference of each hoop is disposed substantially perpendicular to the longitudinal axis of the respective stent. A stent assembly as claimed in claim 14 wherein each hoop comprises a substantially complete turn of the wire. A stent assembly as claimed in claim 14 or 15 wherein the plane of the circumference of the hoop at each longitudinal end of the stent is square to the longitudinal axis of the respective stent. A stent assembly as claimed in any of claims 14-16, further comprising securing means (99) for securing an apex (22) of sinuous wire in one hoop to a juxtaposed apex of a neighbouring hoop so that each hoop is supported by its neighbours. A stent assembly as claimed in claim 17 wherein said securing means comprises a loop element (99c) to tie the juxtaposed apices together. A stent assembly as claimed in any preceding claim wherein said other stent and said one stent consist of a shape memory alloy. An endoluminal prosthesis comprising a stent assembly as claimed in any preceding claim, wherein at least one of said one and other stents comprises a graft layer. A prosthesis as claimed in claim 20 wherein a graft layer is disposed either externally or internally on at least one of said female cooperating portion and said male engaging portion. A prosthesis as claimed in claim 20 or 21 wherein a graft layer is disposed internally on said female cooperating portion. A prosthesis as claimed in claim 20, 21 or 22 wherein a graft layer is disposed externally on said male cooperating portion. A prosthesis as claimed in any of claims 20 to 23 wherein a graft layer is interposed between said female cooperating portion and said male engaging portion to form a substantially blood tight seal. A prosthesis or stent assembly as claimed in any preceding claim further including a radiographic marker disposed on at least one of said stents to facilitate alignment of said stents or insertion of said male cooperating portion in said female cooperating portion.

Inventors: CRAGG ANDREW HAROLD, DAKE MICHAEL DAVID, GOICOECHEA GEORGE, HUDSON JOHN, MIALHE CLAUDE, CRAGG, ANDREW HAROLD, DAKE, MICHAEL DAVID, GOICOECHEA, GEORGE, HUDSON, JOHN, MIALHE, CLAUDE
Applicants: BOSTON SCIENT TECH INC, BOSTON SCIENTIFIC TECHNOLOGY INC.
Application year: 1995
Main classification: A61F2
IPC codes: A61F2, A61M25