WO1998040035A1

WO1998040035A1 - Flexible tissue supporting device

Info

Publication number: WO1998040035A1
Application number: PCT/US1998/005014
Authority: WO
Inventors: Robert L. Hess; Bruce Modesitt; Vaso Adzich; Jerome Jackson
Original assignee: United States Surgical Corporation
Priority date: 1997-03-13
Filing date: 1998-03-13
Publication date: 1998-09-17
Also published as: AU6464298A

Abstract

A tissue supporting device (10) comprises first (A) and second (B) tubular sections interconnected by a bridging section (C). The tubular sections include a continuous strip (20) having aligned segments (22) and curved segments (30) interconnecting the aligned segments. The bridging section includes wavy strips (40), each of which includes a first (42) and second portion (44) inclined in a first direction and interconnected by a third portion (46) inclined in a second direction. The tissue supporting device is of a biocompatible material such as stainless steel, tantalum, gold or shape memory alloy such as a nickel-titanium alloy. The shape memory alloy can have a high transition temperature so that the tissue supporting device is permanently positioned to support the tissue of a tubular organ of a living body. The shape-memory allows the positioned tissue supporting device in the martensitic state and exhibits a strain on a plateau of a stress-strain curve of the shape-memory alloy when permanently positioned in the tubular organ.

Description

FLEXIBLE TISSUE SUPPORTING DEVICE

The present application is a continuation-in-part of pending U.S. Serial No. 08/637,330 filed April 23, 1996, a continuation of Serial No. 08/310,100 filed September 22, 1994, now U.S. Patent No. 5,545,210, the disclosures of which are hereby incorporated by reference.

Field of the Invention

The invention relates to tissue supporting devices (stents), preferably vascular stents for repairing blood vessels, and more particularly, to non-removable devices which will permanently support a dilated stenosis of a tubular organ (hollow viscus) such as a blood vessel.

Background of the Invention In the past, permanent or biodegradable devices have been developed for implantation within a body passageway to maintain vascular patency. These devices are typically characterized by the ability of such an intravascular device to be enlarged radially after having been introduced percutaneously, to be transported transluminally, and to be positioned in a desired location. These devices are either expanded mechanically, such as by the expansion of a mandrel positioned inside the device, or are capable of releasing stored energy to expand themselves upon actuation within the body.

U.S. Patent Nos. 4,739,762, 4,776,337 and 4,733,665 disclose expandable and deformable intraluminal vascular grafts in the form of thin-walled tubular members which are expanded radially outwardly into contact with a body passageway, the members being plastically deformed beyond their elastic limit and the members being permanently fixed within the body. Suitable materials for the fabrication of these tubular-shaped members would include silver, tantalum, stainless steel, gold, titanium, or other suitable plastically deformable materials which may be permanently deformed. Permanent deformation is achieved when the material is^" subjected to a force which creates a strain greater than the elastic limit of the material which is utilized to make the tubular member. The open-mesh configuration of such devices is soon encapsulated by body tissue and cannot be removed. The exceeding of the elastic limit of the material used in such devices is also believed to compromise the performance of the devices in situ.

Articulated prosthetic implants, grafts and stents are disclosed in U.S. Patent Nos. 3,657,744; 5,102,417; 5,104,404; 5,195,984; 5,449,373; and 5,545,210; and WO Publication No. 96/03092.

U.S. Patent No. 4,969,458 discloses a vascular stent formed from a wire component made of material, such as copper alloy, titanium, or gold, wherein the wound configuration unwinds upon expansion and becomes a permanent prosthesis stent, similar to prior art devices disclosed above, and is not removable.

U.S. Patent No. 4,969,890 discloses various configurations of shape-memory alloy members which have been previously radially compressed and which, upon positioning within the body and thermal activation, expand by themselves to become a permanent prosthesis within the body. In this regard, the reference teaches a device which operates in a similar fashion to the device disclosed in U.S. Patent No.

4,485,816. U.S. Patent No. 4,485,816 discloses a shape-memory alloy staple which, when heated, penetrates and cinches tissue together. Shape-memory alloy historically has been used to perform work in such a fashion wherein the component remains in a strong austenitic state after temperature activation. That is, above its transition temperature from martensite to austenite, and as die references above disclose, the shape-memory alloy either dilates an incompetent blood vessel or holds segments of tissue together. Neither of these devices is practically removable by a method which does not require surgery.

Shape-memory alloys possess the useful characteristic of being capable of changing physical dimensions upon heating above a first transition temperature, Af, between a martensitic metallurgical state and a austenitic metallurgical state of the alloys. A shape-memory alloy member can be processed while in a high temperature austenitic phase to take on a first configuration. After cooling the shape-memory alloy member below a second transition temperature Mf between the austenitic and martensitic states without change of physical dimensions, the shape-memory alloy member can be mechanically deformed into a second configuration. The shape- memory alloy member will remain in this second configuration until further heating to a temperature above Af at which time the shape-memory alloy member will revert to its first configuration. A shape-memory alloy member can exert large forces on adjacent members during the transition from the second configuration to the first configuration. Numerous inventions have taken advantage of shape-memory alloy members capable of exerting this thermally activated force.

Shape-memory alloys have the further useful characteristic that, in the martensitic phase, the stress-strain curve exhibits a plateau indicating that a limited increase in strain can be achieved with minimal increase in stress. This martensitic stress-strain plateau usually defines die range of mechanical strain which can be recovered by die application of heat.

U.S. Patent No. 5,197,978, hereby incorporated by reference, discloses shape- memory alloy tissue supporting devices tiiat are made to expand or shrink radially upon mechanical or thermal actuation, and, in particular, devices that are removable from the body.

It would be advantageous to have a flexible tissue supporting device of a generally tubular configuration which can be inserted into a body duct or cavity while in an unexpanded shape and tiien be expanded to provide permanent support for the tissue forming the duct or cavity, such that the device when expanded does not exert a radial load on die supported duct or cavity and where die device when expanded has sufficient crush resistance to provide support for the duct or cavity when the duct or cavity exerts a normal radial compressive load on die device as die result of major contractions of the tissue.

It would be further advantageous to have a flexible tissue supporting device, for simultaneous support of cavities of different sizes, in which larger expanded device sizes do not require substantially higher expansion pressures than smaller device sizes, so that the potential for dissection and/or tissue damage is minimized, and where further the device remains somewhat flexible to accommodate movement of soft tissue. Snmmarv of the Invention

The invention provides a flexible tissue supporting device comprising a first tubular section and a second tubular section interconnected by a bridging section. Each of the first and second tubular sections comprises a continuous strip having aligned segments and curved segments, each of die curved segments interconnecting adjacent ends of a pair of die aligned segments such that each of the aligned segments is connected to an adjacent one of die aligned segments by only one of the curved segments. The bridging section comprises a plurality of wavy strips, each of the wavy strips being connected between one of the curved segments of the first tubular section and one of die curved segments of die second tubular section.

The tissue supporting device can incorporate various features according to various embodiments of die invention. For instance, the aligned segments can be rectilinear and extend in an axial direction and die continuous strip can be uniform or nonunifoπn in cross section. Each of the wavy strips can include a first portion inclined in a first direction witii respect to the aligned segments, a second portion inclined in die first direction, and a tiiird portion inclined in a second direction, die third portion interconnecting die first and second portions and forming acute angles with die first and second portions. The wavy strips can interconnect all or only some of the curved segments at one end of die first tubular section witii all or some of the curved segments at one end of die second tubular section.

According to one embodiment of die invention, die tissue supporting device is expandable from a first configuration to a second configuration wherein the second configuration has a pattern of identically shaped expanded openings. In the first configuration, die aligned segments can abut each other and in die second configuration die aligned segments can form a ring of wishbone-shaped segments. Further, in die first configuration, die wavy strips can abut each otiier and in die second configuration die wavy strips can be spread apart in a circumferential direction while maintaining substantially d e shape they had in die first configuration.

The tissue supporting device can include any desired number of tubular and bridging sections. For instance, die tissue supporting device can include a tiiird tubular section interconnected to die second tubular section by a second bridging section, a fourth tubular section interconnected to die third tubular section by a third bridging section, a fifth tubular section interconnected to d e fourth tubular section by a fourth bridging section, a sixth tubular section interconnected to die fifth tubular section by a fifth bridging section, a seventii tubular section interconnected to die sixth tubular section by a sixtii bridging section, etc. The bridging sections can separate adjacent tubular sections in an axial direction and/or die bridging sections can be interleaved witii die tubular sections. The tubular section and die wavy strips can comprise an etched, an electric discharge machined, or laser-cut tube or sheet of metal. According to one embodiment of the invention, die curved segments can be enlarged curved segments which define a series of teardrop-shaped openings at opposite ends of die first and second tubular sections. Each of die enlarged curved segments can abut another one of die enlarged curved segments prior to expansion of the tissue supporting device. The tissue supporting device can be of a biocompatible material such as stainless steel, nickel-titanium, shape memory alloy, tantalum, gold, or die like. For instance, the device can be comprised of a unitary piece of a shape-memory alloy which transforms from a martensitic metallurgical state to an austenitic metallurgical state when heated above a first transition temperature Af and transforms from the austenitic state to the martensitic state when cooled below a second transition temperature M_f, the tissue supporting device being mechanically deformable without plastic deformation in a body passage of a living person from a first configuration while in the martensitic state to a second configuration in die martensitic state and die Af temperature being sufficiently above a body temperature of the living person to prevent recovery of die tissue supporting device to die first configuration by heating the tissue supporting device above A_f witiiout permanently damaging surrounding tissue of die living person, die tissue supporting device exhibiting a strain on a plateau of a stress-strain curve of the shape-memory alloy when permanentiy positioned in die body passage. Brief Description of the Drawings

Fig. 1 shows a first embodiment of a flexible stent in accordance witii die present invention;

Fig. 2 shows die stent of Fig. 1 in an expanded configuration; Fig. 3 shows a shorter version of die stent shown in Fig. 1;

Fig. 4 shows a modification of die stent shown in Fig. 3;

Fig. 5 shows a portion of die stent shown in Fig. 1;

Fig. 6 shows a second embodiment of a flexible stent in accordance with die invention; Fig. 7 shows a tiiird embodiment of a flexible stent in accordance witii die invention;

Fig. 8 shows a fourth embodiment of a flexible stent in accordance with die invention;

Fig. 9 shows a fifth embodiment of a flexible stent in accordance with die invention;

Fig. 10 shows a sixtii embodiment of a flexible stent in accordance with die invention;

Fig. 11 shows a seventh embodiment of a flexible stent in accordance witii die invention; and Figs. 12 a-p show embodiments of wavy strips in accordance witii die invention.

Detailed Description of the Invention

According to die invention, an axially flexible tissue supporting device is provided which can be inserted into a body passage, such as a blood vessel, duct or cavity, and used to support die tissue forming the duct or cavity. The tissue supporting device can be fabricated from biocompatible materials such as stainless steel, tantalum, gold, or die like, or from a shape memory alloy such as a binary Ni- Ti alloy or NiTi alloy having one or more additional elements added tiiereto. Other possibilities include shape memory alloys from the Cu-Al-Ni system. The tissue supporting device is of a generally tubular shape which can be inserted into a body duct or cavity in an unexpanded shape and tiien be expanded at a desired position in die duct or cavity to form a permanent supporting structure for die tissue surrounding the expanded device.

According to a preferred embodiment, die tissue supporting device comprises a shape memory alloy which exhibits a stress-strain curve wherein an increase in strain can be achieved with a negligible increase in stress. Such shape memory alloys have martensitic and austenitic metallurgical states and a transition temperature therebetween. The shape-memory alloy used according to die invention is characterized by a stress/strain curve in the martensite state wherein a limited increase in strain can be achieved witii minimal increase in stress.

The shape-memory property can be used in manufacturing die tissue supporting device. For instance, a tube of suitable shape-memory material such as Nitinol can be provided witii a desired pattern of openings to create tubular sections interconnected by bridging sections. Then, the tiius patterned tube can be mechanically expanded to a diameter die tissue supporting device will have when deployed in a tubular organ. The thus expanded tube can then be processed to provide a suitable surface finish or other feature. As an example, the internal surface finish can be provided by techniques such as honing and or polishing. Subsequendy, the processed tube can be shrunk by heating the tube to a temperature to transform the tube material into the austenitic state to thereby recover die original diameter of die tube, i.e. the tube's memorized configuration. Accordingly, die tissue supporting device is tiius returned to a size which can be surgically delivered and subsequently mechanically expanded such as by a balloon catheter within a tubular organ of a patient. As an example, in the case where the tissue supporting device is a cardiovascular stent, the stent can be mechanically expanded in its martensitic condition to a diameter of 4 to 4.5 mm thus providing a greater surface area for surface finishing such as by polishing or honing to remove any sharp edges, etc., after which die stent can be shrunk to its original size by the heating the stent into its austenitic state. In this way, a better internal surface finish can be obtained on die stent due to its processing in die mechanically expanded state. A tissue supporting device according to die invention can be made from a Ni- Ti alloy whose tensile strength in the martensitic state at human body temperature is 8 to 25 ksi. According to one embodiment of die invention, die transition temperature at which the alloy transforms from the martensitic to the austenitic state is preferably at a temperature of 70°C or higher. At such temperatures, known thermal recovery techniques for shrinking shape memory alloy tubular devices cannot be used to recover die tissue supporting device without causing permanent damage to surrounding tissue or blood due to thermal trauma which has been found to occur when tissue/blood is exposed to temperatures above 62 °C. A first embodiment of die invention is illustrated in Figs. 1 and 2 wherein the tissue supporting device 10 comprises a first tubular section A and a second tubular section B interconnected by a bridging section C. Figs. 1 and 3-11 show die device 10 as a flattened sheet of material which can be formed into a tubular shape such as by rolling the sheet into a tube and welding opposed edges of die sheet. However, the device 10 can be made directly from a tubular material, as explained earlier.

Each of the first and second tubular sections A, B comprises a continuous strip 20 having aligned segments 22 and curved segments 24 separated by slits 30, each of die curved segments 24 interconnecting adjacent ends of a pair of die aligned segments 22. The bridging section C comprises a plurality of wavy strips 40 connected between one of die curved segments 24 of the first tubular section A and one of die curved segments 24 of the second tubular section B. As shown in Fig. 1, each of the aligned segments 22 is connected to an adjacent one of die aligned segments 22 by only one of die curved segments 24. Although the aligned segments 22 are shown as rectilinear and extending in an axial direction, d e aligned segments can have any desired configuration. Likewise, while the continuous strip 20 is shown as having a uniform cross section, the cross section of die aligned segments can be nonuniform in cross section.

As shown in Fig. 3, the tissue supporting device 10 can include four tubular sections A, B, D and E interconnected by tiiree bridging sections C, F and G. However, die tissue supporting device can include any desired number of tubular sections and in die embodiment shown in Fig. 1, die tissue supporting device includes seven short tubular sections interconnected by six bridging sections. A tissue supporting device comprised of such short tubular sections connected togetiier by wavy strip bridging members 40 creates a tissue supporting device witii die advantage of greater axial flexibility, i.e., the center axis of the tissue supporting device is easier to bend. This greater axial flexibility enables die device to be deployed tiirough a more tortuous patii. In addition, a tissue supporting device containing short tubular sections connected together by wavy strip bridging members 40 creates a device witii the advantages of large perimeter side openings. The large perimeter side openings 50 provide access to side branching blood vessels while the bridging section minimizes spacing between the tubular sections to minimize prolapse of tissue between the tubular sections. The wavy strip bridging members 40 allow expansion of die tubular sections and formation of large perimeter side openings 50 while maintaining any desired axial spacing between the tubular sections. Further, as shown in Fig. 4, one or more of die wavy strips 40 can be omitted to create an opening 60 for access to side branches or accommodate a bifurcated vessel. For instance, the opening 60 can be used to allow a guide wire to pass axially through die tissue supporting device 10 and radially outwardly tiirough de opening 60.

As shown in Fig. 1, each of die wavy strips 40 includes a first portion 42 inclined in a first direction with respect to the aligned segments 22, a second portion 44 inclined in die first direction, and a tiiird portion 46 inclined in a second direction, the third portion 46 interconnecting the first and second portions 42, 44. In die embodiment shown in Fig. 1, die wavy strips 40 interconnect all of the curved segments 24 at one end of die first tubular section A witii all of the curved segments 24 at one end of die second tubular section B. However, in the embodiment shown in Fig. 6, die wavy strips 48 connect only some of die curved segments 26 at one end of die first tubular section A witii some of die curved segments 46 at one end of the second tubular section B.

In die embodiment shown in Fig. 6, some of die curved segments 26 are enlarged curved segments which define a series of teardrop-shaped openings 28 at opposite ends of die first and second tubular sections A, B. Each of the enlarged curved segments 26 abuts another one of die enlarged curved sections 26 in d e flattened state shown in Fig. 6. However, when the device is formed into a tubular shape, die enlarged curved segments 26 will eitiier be abutting adjacent enlarged curved sections 26 or be located close diereto prior to expansion of the tissue supporting device. Fig. 2 shows a perspective view of the expanded condition of the tissue supporting device 10 shown in Fig. 1. As shown in Fig. 2, in die expanded condition, die tissue supporting device includes a pattern of identically shaped open areas 50 and die aligned segments 22 form a ring of wishbone-shaped segments. Further, comparing Fig. 1 to Fig. 2, the tissue supporting device 10 is expandable from a first configuration in which die wavy strips 40 abut each other to a second configuration in which the wavy strips 40 spread apart in a circumferential direction and maintain their shape.

Fig. 7 shows an embodiment wherein the tissue supporting device 10 includes a continuous strip 70 formed by aligned segments 72,74,76,78, aligned segments 72,74 being parallel to each other and aligned segments 76,78 being parallel to each other but segments 72,74 not being parallel to segments 76,78. In addition die device 10 in Fig. 7 includes bridging members 80 which extend between a concave portion 82 of a curved segment of a first tubular section and a convex portion 84 of a curved segment of a second tubular section. Thus, the wavy strips 80 are interleaved between aligned segments 74,76. Additional wavy strips 86 having a pair of bends 87 extend between concave portions 88 of curved segments of two adjacent tubular sections with die wavy strips 86 interleaved between aligned segments 74,76. The device 10 shown in Fig. 8 includes wavy strips 80 extending between concave portions 82 and convex portions 84 of curved segments but is odierwise similar to the tissue supporting device shown in Fig. 7.

Fig. 9 shows an embodiment similar to Fig. 7 except that aligned segments 72a, 74a are generally parallel witii aligned segments 76a, 78a whereas in Fig. 7 aligned segments 72, 74 are parallel witii each otiier but not witii aligned segments 76, 78. Fig. 10 shows an embodiment similar to Fig. 7 except that wavy strips 86a include a pair of bends 86b oriented in die same manner whereas the wavy strips 86 in Fig. 7 include bends 87 which are mirror images of each other. Fig. 11 shows an embodiment wherein die tissue supporting device 10 includes tubular sections comprising a continuous strip formed by aligned segments 92, 94 and curved segments 96, the device further including wavy strips 98 connecting curved segments 96 of one tubular section to curved segments 96 of an adjacent tubular section. In die Fig. 11 embodiment, die wavy strips 98 are continuous and circumferentially spaced apart by expandable members such which, for example, can comprise a pair of adjacent aligned segments 92, 94 and attached pair of the curved segments 96. In the foregoing embodiments, an advantage of die interleaved bridging segments is that the tissue supporting device does not shorten axially upon expansion of the device. Figs. 12 a-p show embodiments of wavy strips which can be used to form all or part of the bridging sections of the tissue supporting device. The wavy strips can have various configurations such as a sine wave shape as shown in Figs. 12 a-b having one or more repeating portions 102, a triangular wave shape as shown in Figs. 12 c-f having one or more repeating portions 104 wherein the triangles form acute angles or right angles, an acute biphasic triangular wave shape as shown in Figs. 12 g-h witii one or more repeating portions 106, a low amplitude biphasic triangular wave shape as shown in Figs. 12 i-j witii one or more repeating portions 108, a square wave shape as shown in Figs. 12 k-1 witii one or more repeating portions 110, a bilevel square wave shape as shown in Figs. 12 m-n with one or more repeating portions 112, or a ramp wave shape as shown in Figs. 12 o-p with one more repeating portions 114. However, alternative designs of the wavy strips can also be used, if desired.

The stent-like member 10 according to die claimed invention, when fabricated from a Ni-Ti shape-memory alloy, can be expanded in a blood vessel to a range of desired sizes by inflating a balloon catheter to a pressure of 4-10, preferably 6-8 atmospheres of pressure in the balloon catheter. When the stent is expanded, die slits 30 are enlarged into one or more groups of identically shaped openings arranged in a uniform pattern. For instance, die tissue supporting device can include first and second groups of openings, the first group of openings having a different shape than the second group of openings. In each of the embodiments, expansion of the individual sections can be performed separately to achieve different diameters. Due to the expansion in the martensitic condition, sections expanded to larger sizes do not require substantially higher expansion pressures tha sections expanded to smaller sizes provided tiiat the tissue supporting device comprises sections made from die same generally tubular shape-memory alloy material. This embodiment offers die advantage of minimizing the potential for dissection and/or tissue damage.

The stent-like member 10 can be positioned at its application site in a low profile configuration with radial dimensions small enough to allow navigation of orifice and ducts leading to die site of application. The stent-like member 10 can be positioned by means of a balloon catiieter device having a lumen portion, balloon portion, and guide portion with the stent-like member 10 surrounding die balloon portion. In a preferred embodiment, stent-like member 10 is mechanically crimped securely to the balloon portion prior to insertion of the balloon catiieter device in a blood vessel.

In a preferred embodiment, die balloon portion is expanded, tiius deforming stent-like member 10 radially outward against an inner wall of a blood vessel, and forming a supporting structure for the blood vessel. The expansion of the stent-like member according to die invention takes place in die elastic region of the stress-strain curve defined by die plateau in tiiat curve. The deformed stent-like member 10 can comprise any of the specific shapes shown in Figs. 1-11 or any other suitable shape which can be mechanically deformed without peπnanentiy deforming the device. The stent is designed so that the strain in the expanded stent-like member 10 is controlled such as by the length of die tubular sections, bridging sections, and/or slits 30. Use of a shape memory NiTi alloy for the device is also advantageous since such material can exhibit anti-thrombotic properties. Once the balloon catheter has been removed by collapsing die balloon portion, stent-like member 10 is left implanted to permanently support the blood vessel. The overall geometry of the stent-like member 10 ensures that the snapback at expansion is minimized and is proportional to die expanded size of the stent-like member 10. Since d e implanted stent-like member exhibits a strain on a plateau of a stress-strain curve for the shape-memory alloy, the stent-like member can support the blood vessel at essentially constant stress. The expanded dimensions of the stent-like member 10 cannot be adjusted by die amount of force used to expand die device. Instead, die expanded diameter is controlled by die dimensions of die duct, cavity or, blood vessel, into which the stent-like member 10 is expanded. According to die invention, the shape memory alloy of the stent-like member 10 remains in the martensitic state when die stent-like member 10 is in service in a human body.

The duct supportive properties of an implanted member can be controlled by die alloy composition, processing conditions, wall thickness of shape-memory alloy forming the tube-like member, die lengtii of tubular sections A, B, etc., and lengtii of die bridging sections B, etc., and by die degree of expansion of die stent-like member 10. An implanted stent-like member 10 has sufficient crush resistance to provide support for a duct or cavity or blood vessel when such duct or cavity or blood vessel exerts a normal radial compressive load on die stent-like member 10 as the result of a major contraction of die duct or cavity or blood vessel. Preferably the stent-like member 10 can be sufficiently robust to support a coronary artery when major contractions are indicated. The implanted stent-like member 10 essentially does not exert a radial load on die duct or cavity or blood vessel it is supporting. The implanted stent-like member 10 allows for a small amount of radial recoverable deflection at low loads as die supported duct or cavity or blood vessel contracts. The low force needed to cause elastically recoverable deflection of stent-like members 10 in response to tissue duct contraction can advantageously minimize irritation to the duct wall when small contractions occur.

Although the invention has been described as useful in an angioplasty procedure, it is understood tiiat the invention is not limited to such a procedure or die use of a stent-like member in a blood vessel. It should be apparent to one skilled in die art that the invention is useful in supporting body tissue in general as well as various blood vessels, e.g., in saphenous vein grafts, the vena cavae, the aorta, the renal artery, the iliac artery, the femoral artery, the popliteal artery, the carotid artery, the cranial arteries, pulmonary arteries, etc. The various embodiments of the invention are also useful with other tubular organs including but not limited to die prostate, biliary tract, the esophagus, the trachea, the Fallopian tubes, the vas deferens, die ureters, the tear ducts, die salivary ducts, etc. The tissue supporting device according to die claimed invention can nonmagnetic and corrosion resistant thus making it more compatible with specialized imaging methods involving electromagnetic waves, i.e., magnetic resonance imaging ("MRI"). Further, die tissue supporting device can include means for making the stent visible and radiopaque under conventional fluoroscopes when in the human body. For instance, the radial wall tiiickness of the tissue supporting device can be any suitable thickness such as 0.003 inches to 0.020 inches, thus making the stent visible by radiopaque techniques.

The stent according to die invention can provide benefits in preventing thrombogenic response. In particular, die stent geometry can be controlled to provide a planar cylindrical profile when expanded witii minimal strut twisting and outwardly protruding stent strut terminations. That is, whereas the struts forming the mesh-like structure of stainless steel stents have a tendency to twist such tiiat the edges tiiereof project radially outwardly when expanded by balloon inflation, the stent according to die invention can be expanded widiout such twisting of die various segments thereof. Further, compared to a stainless steel stent having the same configuration, the stent according to die invention can be expanded at much lower balloon expansion pressures. The lower expansion pressures used in accordance witii the invention minimize barotrauma and the smooth outer cylindrical surface of die expanded stent in accordance witii die invention provides non-dirombogenic properties.

The foregoing has described die principles, preferred embodiments and modes of operation of die present invention. However, die invention should not be construed as being limited to e particular embodiments discussed. Thus, die above-described embodiments should be regarded as illustrative ratiier than restrictive, and it should be appreciated tiiat variations may be made in tiiose embodiments by workers skilled in die art without departing from me scope of die present invention as defined by die following claims.

Claims

WHAT IS CLAIMED IS:

1. A flexible tissue supporting device comprising: a first tubular section and a second tubular section interconnected by a bridging section; each of the first and second tubular sections comprising a continuous strip having aligned segments and curved segments, each of the curved segments interconnecting adjacent ends of a pair of the aligned segments such that each of the aligned segments is connected to an adjacent one of the aligned segments by only one of die curved segments; and die bridging section comprising a plurality of wavy strips, each of the wavy strips being connected between one of die curved segments of the first tubular section and one of die curved segments of me second tubular section.

2. The tissue supporting device of Claim 1, wherein each of the wavy strips comprises one or more repeating shapes.

3. The tissue supporting device of Claim 1, wherein each of the curved segments at one end of die first tubular section is connected to one of the wavy strips.

4. The tissue supporting device of Claim 1, wherein the aligned segments are rectilinear and extend in an axial direction.

5. The tissue supporting device of Claim 1, wherein die continuous strip is substantially uniform in cross section.

6. The tissue supporting device of Claim 1, wherein only every other one of die curved segments at one end of d e first tubular section is connected to one of the wavy strips.

7. The tissue supporting device of Claim 1, wherein each of the wavy strips connects a concave portion of one of curved segments to a convex portion of another one of die curved segments.

8. The tissue supporting device of Claim 7, wherein only every other one of die curved segments at one end of die first tubular section is connected to one of the wavy strips.

9. The tissue supporting device of Claim 1, wherein each of the wavy strips includes a first portion inclined in a first direction with respect to the aligned segments, a second portion inclined in die first direction, and a third portion inclined in a second direction, die third portion interconnecting the first and second portions and forming acute angles with die first and second portions.

10. The tissue supporting device of Claim 9, wherein the wavy strips interconnect all of the curved segments at one end of die first tubular section with all of the curved segments at one end of die second mbular section.

11. The tissue supporting device of Claim 1, wherein the wavy strips interconnect only some of the curved segments at one end of die first tubular section with only some of the curved segments at one end of die second tubular section.

12. The tissue supporting device of Claim 1, wherein the tissue supporting device is expandable from a first configuration to a second configuration, the second configuration having a pattern of only identically shaped expanded openings.

13. The tissue supporting device of Claim 1, wherein the tissue supporting device is expandable from a first configuration in which the aligned segments abut each other to a second configuration in which the aligned segments form a ring of wishbone-shaped segments.

14. The tissue supporting device of Claim 1, wherein the tissue supporting device is expandable from a first configuration in which the wavy strips abut each other to a second configuration in which the wavy strips are spread apart in a circumferential direction and maintain substantially the same shape as in the first configuration.

15. The tissue supporting device of Claim 1, wherein the tissue supporting device includes a tiiird tubular section interconnected to die second mbular section by a second bridging section.

16. The tissue supporting device of Claim 15, wherein the tissue supporting device includes a fourth tubular section interconnected to die tiiird mbular section by a third bridging section.

17. The tissue supporting device of Claim 16, wherein the tissue supporting device includes a fifth mbular section interconnected to die fourth mbular section by a fourth bridging section.

18. The tissue supporting device of Claim 17, wherein the tissue supporting device includes a sixtii tubular section interconnected to die fifth tubular section by a fifth bridging section.

19. The tissue supporting device of Claim 18, wherein the tissue supporting device includes a seventii mbular section interconnected to die sixtii tubidar section by a sixtii bridging section.

20. The tissue supporting device of Claim 1, wherein some of the curved segments are enlarged curved segments which define a series of teardrop-shaped openings at opposite ends of die first and second tubular sections.

21. The tissue supporting device of Claim 20, wherein each of the enlarged curved segments abuts another one of die enlarged curved segments.

22. The tissue supporting device of Claim 1, the mbular and bridging sections being comprised of a unitary piece of a shape-memory alloy which transforms from a martensitic metallurgical state to an austenitic metallurgical state when heated above a first transition temperature A_f and transforms from the austenitic state to the martensitic state when cooled below a second transition temperature M_f, the tissue supporting device being mechanically deformable without plastic deformation in a body passage of a living person from a first configuration while in the martensitic state to a second configuration in die martensitic state and die A_f temperature being sufficiently above a body temperature of die living person to prevent recovery of the tissue supporting device to die first configuration by heating the tissue supporting device above A_f witiiout permanently damaging surrounding tissue of the living person, the tissue supporting device exhibiting a strain on a plateau of a stress-strain curve of the shape-memory alloy when permanendy positioned in die body passage.

23. The tissue supporting device of Claim 1, wherein the first mbular section, the second tubular section and die wavy strips comprise an etched, electric discharge machined or laser-cut tube or sheet of metal.

24. The tissue supporting device of Claim 23, wherein die metal is selected from the group consisting of stainless steel, nickel-titanium, shape memory alloy, tantalum, gold, and biocompatible metallic material.

25. The tissue supporting device of Claim 22, wherein the shape-memory alloy is an alloy of Ni and Ti having radiopacity and/or Af ΓëÑ 62 ┬░C and/or die tissue supporting device includes a coating providing a surface finish which minimizes thrombosis.

26. The tissue supporting device of Claim 1, wherein the curved segments at one end of each of die aligned segments is connected to the curved segment of an adjacent one of die aligned segments by a portion of one of the bridging members, each of the bridging members comprising a continuous wavy strip extending die entire length of the tissue supporting device.

27. A flexible tissue supporting device comprising: a first tubular section and a second tubidar section interconnected by a bridging section, each of the mbular sections including aligned segments and curved segments, each of the aligned segments being connected to an adjacent one of the aligned segments by only one of die curved segments, the bridging section comprising a plurality of wavy strips, each of the wavy strips being connected between one of die curved segments of the first tubular section and one of die curved segments of die second mbular section, each of die wavy strips including a first portion inclined in a first direction, a second portion inclined in the first direction, and a tiiird portion inclined in a second direction, die tiiird portion interconnecting the first and second portions and forming acute angles with die first and second portions.

28. A flexible tissue supporting device comprising a first mbular section and a second tubular section interconnected by a bridging section, each of the first and second tubular sections comprising a continuous strip having aligned segments and curved segments, each of the curved segments interconnecting adjacent ends of a pair of die aligned segments, die tissue supporting device being expandable from a first configuration in which die aligned segments abut each otiier to a second configuration in which the aligned segments form a ring of wishbone-shaped segments.

29. A flexible tissue supporting device comprising a first tubular section and a second tubular section interconnected by a bridging section, each of die first and second tubular sections comprising a continuous strip having aligned segments and curved segments, each of the curved segments interconnecting adjacent ends of a pair of the aligned segments, some of die curved segments being enlarged curved segments which define a series of teardrop-shaped openings at opposite ends of die first and second tubular sections.

30. A flexible tissue supporting device comprising a first tubular section and a second tubular section interconnected by a bridging section, each of the tubular sections including aligned segments and curved segments, the bridging section comprising a plurality of wavy strips, the tubular and bridging sections being comprised of a unitary piece of a shape-memory alloy which transforms from a martensitic metallurgical state to an austenitic metallurgical state when heated above a first transition temperature Af and transforms from the austenitic state to the martensitic state when cooled below a second transition temperature M_f, the tissue supporting device being mechanically deformable without plastic deformation in a body passage of a living person from a first configuration while in the martensitic state to a second configuration in the martensitic state and die Af temperature being sufficientiy above a body temperature of die living person to prevent recovery of the tissue supporting device to die first configuration by heating die tissue supporting device above A_f without permanently damaging surrounding tissue of the living person, the tissue supporting device exhibiting a strain on a plateau of a stress-strain curve of die shape-memory alloy when permanently positioned in die body passage.

31. A tubular tissue supporting device comprising a plurality of circumferentially spaced apart wavy strips, each of the wavy strips being continuous and extending axially along die entire length of die tissue supporting device, each of die wavy strips being connected to an adjacent one of the wavy strips by expandable members.