Stents with attached looped ends

Abstract

An open frame prosthesis is formed with looped end terminations at its proximal and distal ends. At one end of the prosthesis, the filaments or strands are welded together in pairs to form strand couplings. A plurality of loop segments are connected to the strand couplings, one loop segment for each pair of adjacent strand couplings. In one version of the prosthesis, strands at the opposite end are bent to form looped ends. In another version, loop segments are connected to pairs of strand couplings at both ends of the prosthesis. The loop segments can be connected to the couplings by welding, fusion bonds, or tubes, which are either crimped or heat shrunk.

Claims

1. A prosthesis comprising: a plurality of wires forming a mesh, wherein terminal ends of the plurality of wires are Joined together at a first end of the mesh to form a plurality of strand junctions; and spaced apart loops at the first end of the mesh, defining a spaced apart loop for each pair of adjacent strand junctions, each spaced apart loop formed from: a first strand junction of the plurality of strand junctions consisting of a terminal end of a first wire of the plurality of wires forming the mesh and a terminal end of a second wire of the plurality of wires forming the mesh, a second strand junction of the plurality of strand junctions consisting of a terminal end of a third wire of the plurality of wires forming the mesh and a terminal end of a fourth wire of the plurality of wires forming the mesh, wherein the terminal end of the first wire is longer than the terminal end of the second wire to provide a strand extension extending beyond the terminal end of the second wire and looping back to be attached to and axially aligned with the second strand junction.

2. The prosthesis of claim 1, the mesh comprising a second end having loops.

3. The prosthesis of claim 2, each spaced apart loop providing a smooth, rounded, blunt end.

4. The prosthesis of claim 2, each spaced apart loop is a blunt and flexible end termination.

5. The prosthesis of claim 2, the spaced apart loops being equally angularly spaced apart from one another.

6. The prosthesis of claim 1, the plurality of wires helically wound in a first direction over a longitudinal length of the mesh and in a second direction over the longitudinal length of the mesh.

7. The prosthesis of claim 1, the first and second strand junctions secured by welds.

8. The prosthesis of claim 1, the first and second strand junctions secured by adhesives.

9. The prosthesis of claim 1, the mesh having at least one atraumatic end.

10. A prosthesis comprising: a plurality of wires forming a mesh having a longitudinal length, wherein terminal ends of the plurality of wires are joined together at a first end of the mesh to form a plurality of strand junctions; and spaced apart loops at the first end of the mesh, defining a spaced apart loop for each pair of adjacent strand junctions, each spaced apart loop formed from: a first strand junction of the plurality of strand junctions consisting of a terminal end of a first wire of the plurality of wires forming the mesh and a terminal end of a second wire of the plurality of wires forming the mesh secured together, a second strand junction of the plurality of strand junctions consisting of a terminal end of a third wire of the plurality of wires forming the mesh and a terminal end of a fourth wire of the plurality of wires forming the mesh secured together, wherein the terminal end of the first wire is longer than the terminal end of the second wire to provide a strand extension extending beyond the terminal end of the second wire and looping back to be attached to and axially aligned with the second strand junction; and further wherein: each wire of the plurality of wires comprises nitinol; the plurality of wires are helically wound in a first direction over the longitudinal length of the mesh and in a second direction over the longitudinal length of the mesh; and the mesh has a variable diameter wherein at least one end region of the mesh has a larger diameter than a middle portion of the mesh.

11. The prosthesis of claim 10, further comprising a second end region, wherein the second end region has a larger diameter than the middle portion.

12. The prosthesis of claim 10, wherein the second strand junction and the strand extension are welded together.

13. The prosthesis of claim 10, wherein each spaced apart loop has an apex.

14. A prosthesis comprising: a tubular stent having a first end and a second end; a plurality of wires forming a mesh of the tubular stent, wherein terminal ends of the plurality of wires are joined together at a first end of the tubular stent to form a plurality of strand junctions and each of the plurality of wires forming the mesh extends from the first end of the tubular stent to the second end of the tubular stent; and spaced apart loops formed with the plurality of wires at the first end of the tubular stent, defining a spaced apart loop for each pair of adjacent strand junctions, each spaced apart loop formed from: a first strand junction of the plurality of strand junctions consisting of a terminal end of a first wire of the plurality of wires forming the mesh and a terminal end of a second wire of the plurality of wires forming the mesh, a second strand junction of the plurality of strand junctions consisting of a terminal end of a third wire of the plurality of wires forming the mesh and a terminal end of a fourth wire of the plurality of wires forming the mesh, wherein the terminal end of the first wire is longer than the terminal end of the second wire to provide a strand extension extending beyond the terminal end of the second wire and looping back to be attached to and axially aligned with the second strand junction.

15. The prosthesis of claim 14, wherein the second strand junction and the strand extension are welded together.

16. The prosthesis of claim 14, the mesh having a variable diameter wherein at least one end region of the mesh has a larger diameter than a middle portion of the mesh.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a further understanding of the above and other features and advantages, reference is made to the following detailed description and to the drawings, in which:

(2) FIG. 1 is a side view of a conventional braided stent;

(3) FIGS. 2 and 3 illustrate known alternative open frame prosthesis constructions;

(4) FIG. 4 is a side view, partially in section, showing a braided stent constructed according to the present invention, contained within a deployment and delivery device;

(5) FIG. 5 is a side view of the stent of FIG. 4, in a relaxed state;

(6) FIG. 6 is an enlarged view of one end of the stent;

(7) FIG. 7 is a proximal end view of the stent;

(8) FIGS. 8-10 illustrate several stages in the fabrication of the stent;

(9) FIGS. 11-15 illustrate end regions of alternative embodiment prostheses;

(10) FIG. 16 is a side view of a further alternative embodiment prosthesis with welded loops at both ends; and

(11) FIG. 17 illustrates a component for positionally adjusting or retrieving the stent of FIG. 16 after its deployment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(12) Turning now to the drawings, there is shown in FIG. 4 a stent 16 fabricated according to the present invention, and part of a device 18 used to intraluminally deliver the stent to an intended treatment site and deploy the stent at the treatment site.

(13) The device includes an elongate, flexible outer catheter 20 having a distal end region 22, along which the outer catheter surrounds stent 16 and maintains the stent in a reduced-radius, axially elongated delivery state to facilitate an intraluminal delivery of the stent to the treatment site.

(14) Stent 16 is contained within a lumen 24, which runs substantially the entire length of the outer catheter. An inner catheter 26, contained in the lumen, extends lengthwise along the outer catheter and is moveable axially relative to the outer catheter. A deployment member 28 is fixed to inner catheter 26, proximally of stent 16. Inner catheter 26 includes a lumen (not shown) to accommodate a guidewire 30, which is used to guide the inner and outer catheters to the treatment site. When outer catheter 20 is moved proximally relative to inner catheter 26, the deployment member is encountered by the proximal end of the stent, whereupon further proximal movement of the outer catheter progressively releases the stent from the outer catheter, allowing the stent to radially self-expand into contact with surrounding tissue.

(15) Stent 16 is composed of oppositely directed helically wound strands or filaments 32 that intersect one another to form multiple intersections or crossing points. Strands 32 are interbraided in a one-over-one-under pattern. At the distal end of stent 16, strands 32 are bent to form distal end loops 33. Preferably the strands are formed of a superelastic alloy of titanium and nickel sold under the brand name Nitinol. Other suitable strand materials include cobalt-based alloys such as those sold under the brand names Elgiloy or Phynox, MP35N alloy, and certain stainless steels. Suitable nonmetallic alternatives include polymers, for example polyester and polyethylene terephthalate (PET).

(16) Strands 32 are resilient, and when maintained as shown in FIG. 4 store an elastic restoring force. When released from outer catheter 20, stent 16 self-expands under the restoring force, toward a normal or relaxed state shown in FIG. 5 that stent 16 assumes when under no external stress. As a result of its braided construction and helical strand shapes, stent 16 shortens axially as it expands radially. When the deployed in a blood vessel or other body lumen, stent 16 engages surrounding tissue before it expands fully to the relaxed state. Thus, the deployed stent exerts a radially outward force against the tissue that tends to anchor the stent at the treatment site.

(17) One of the challenges to the physician using device 18 is to accurately place the stent. Accurate placement is made more difficult by the axial shortening of the stent as it enlarges radially. Once the stent is fully deployed, it is contiguous with and frequently partially embedded into the surrounding tissue. As a result, it is difficult to adjust the position of the stent to correct a less than accurate placement. With prostheses constructed as shown in FIGS. 1-3, proximal stent adjustment is particularly difficult because of the stiff welded and/or twisted strand couplings with abrupt proximal ends that present the risk of injury to tissue.

(18) In accordance with the present invention, the proximal end of stent 16 is formed with a series of loop segments. Specifically, six loop segments 34-44 are formed in conjunction with twelve strand junctions or couplings 46. Each loop segment acts as a closure member, cooperating with its associated pair of strand couplings and the coupled strands to form a closed loop end termination. Each loop segment is formed with an extension of one of the coupled strands. For example, FIG. 6 shows a strand junction 46a including strands 32a and 32b, coupled to each other by a weld 48. Similarly, strands 32c and 32d are joined by a weld 50 to form a strand junction 46b.

(19) Strand 32b is longer than the other strands by a predetermined length, to provide a proximal strand extension or portion 52 extending beyond the other strands, which is shaped to provide loop segment 34. Loop segment 34 has several discrete elements, including opposed axially extending legs 54 and 56, opposite inclined linear side sections 58 and 60, a curved proximal end apex 62, and a pair of arcuate sections 64 and 66, each between one of the legs and side sections. A portion of leg 56 is axially aligned with junction 46b, and is connected to that coupling by a weld 68. The remaining loop segments 34-44 are formed in the same manner.

(20) Stent 16 after deployment can be moved proximally along the body lumen without the risk of trauma to the surrounding tissue. Apex 62 and its counterparts on the other loop segments provide smooth, rounded, blunt proximal end terminations with no tendency to poke or cut into tissue as the stent is moved. Also, the loop segments are considerably more flexible than the strand end junctions, regardless of whether the strands are twisted. This is primarily due to strands 32, which are bendable about tangential axes both proximally and distally of junctions 46 to carry apex 62 and its counterparts radially inward. This affords a localized (proximal) radial contraction of the stent to facilitate pulling the stent proximally along the lumen while the majority of the stent remains in contact with surrounding tissue.

(21) Apex 62 further is bendable about radial axes, to bring the legs and side sections closer to one another during radial contraction. Arcuate sections 64 and 66 also are bendable about radial axes, although unlike the apex, they bend in the direction of increasing radii of curvature during radial contraction of the stent. As a result, legs 54 and 56 tend to retain their axial orientation during radial contraction of the stent.

(22) As illustrated in FIG. 7, loop segments 34-44 are arranged symmetrically about the proximal end of the stent, equally angularly spaced apart from one another. Radial contraction of stent 16 not only bends each loop segment into a narrower configuration, but also reduces the gaps between adjacent loop segments. The extent of permitted radial contraction is limited by the amount of bending permitted in each loop segment, particularly at the apex. A salient feature of the present invention is the association of single loop segments with pairs of strand junctions, which reduces the number of loops by one-half, as compared to the conventional loops formed by bending the strands at one end of the stent. Thus, the proximal end of stent 16, as compared to its distal end, is contractible to a smaller diameter.

(23) Stent 16 is fabricated, first by helically winding strands 32 onto a shaping mandrel 70. While FIG. 8 shows only one strand 32a wound about the mandrel, it is to be appreciated that all of the strands are wound simultaneously onto the mandrel to form the braided structure. From a first end 72, strand 32a is wound helically about mandrel 70 until it approaches a remote end 76 of the mandrel, where the strand is trained about a pin 78 to form one of bends 33. Then, the strand is wound helically about the mandrel in the opposite direction, to a proximate end 82. Each strand forms two helical runs or passes over the axial length of the stent. In stent 16, twelve strands form twenty-four such runs. At the proximal end of the mandrel, the ends of the strands form twelve junctions 46.

(24) FIG. 9 shows two of the strand junctions, representing four strand ends, disposed on mandrel 70. Strand 32b includes portion 52 extending axially beyond the rest of the strands. Three pins 84 are fixed to the mandrel, axially outwardly of the strand couplings. Extension 52 of strand 32b is bent about each of pins 84. Its free end 86 is positioned against strand 32c, then attached to strand 32c by welding.

(25) At this stage, mandrel 70 is placed in an oven (or the mandrel is heated) to a heat the strands to a heat set temperature. The heat set temperature, while much lower than the melting temperature for the strand material, is sufficient to relax the strands such that they are amenable to shaping. When the braided structure cools after heat setting, each strand retains its helical shape, and the strands cooperate to determine the relaxed-state tubular shape of the braided structure. Shape memory alloys such as Nitinol are particularly well suited for this process.

(26) FIG. 11 is a view similar to that in FIG. 6, showing part of a stent 90 with an alternative loop forming arrangement in which a strand 92a (rather than 92b) is longer than the other strands and provides the loop segment. In addition, a free end 94 of strand 92a is positioned adjacent strand 92d, rather than 92c, then welded to a junction 96b as before. This can be conveniently considered and “outside-to-outside” connection, as opposed to the “inside-to-inside” connection shown in FIG. 6. For stents of a given size, outside-to-outside connections form slightly wider loop segments.

(27) FIG. 12 shows another alternative arrangement in which hypotubes are used in lieu of welds to secure adjacent portions of the strands. The connections for one of the loop segments are formed by sliding a hypotube 98 over strands 100a and 10b, sliding a hypotube 102 over strands 100c and 100d, shaping an extension 104 of strand 100b and inserting its free end into hypotube 102, then crimping the hypotubes to provide a friction fit that anchors the strands to one another. The hypotubes preferably are formed of steel.

(28) In similar alternative arrangements, tubes 98 and 102 can be formed of elastomeric materials and provide a friction fit, augmented with an adhesive if desired. In another alternative, tubes 98 and 102 are heat shrunk onto the adjacent strands.

(29) FIG. 13 shows part of the proximal end of a polymeric stent 106, specifically polymeric strands 108a and 108b forming a junction 110a, and polymeric strands 108c and 108d forming a junction 110b. The strand junctions are formed by fusion bonding. In addition, an extension 112 of strand 108b is shaped to provide a loop segment, and its free end is connected to strand 108c, again by fusion bonding. The fusion bonds are preferably formed simultaneously, although they can be formed seially.

(30) FIG. 14 illustrates a proximal end region of an alternative stent 114 in which strands 116a and 116b are welded to form a strand coupling 118a, and strands 116 and 116d are welded into a strand coupling 118b. None of strands 116a-d extends axially beyond the others. Thus, none of strands 116 is shaped to provide end closure. Instead, loop closure is provided by a generally U-shaped strand segment 120. The U-shaped strand segment 120 can also be referred to as a loop member. The strand segment includes counterparts to the elements described in connection with loop segment 34a, including opposed legs 122 and 124, side sections 126 and 128, an apex 130, and arcuate sections 132 and 134. As can be seen in FIG. 14, a medial portion of the U-shaped strand segment 120 extends between the legs 122, 124 and is formed by the side sections 126, 128 and the apex 130. Also, as can be seen in FIG. 14, the ends of the U-shaped strand segment 120 and the ends of the strands 116 are oriented in opposite directions with the ends of the U-shaped strand segment 120 being oriented towards a first end of the stent and the ends of the strands 116 being oriented towards a second end of the stent. As further shown in FIG. 14, the medial portion of the U-shaped strand segment 120 is oriented so that apex 130 is oriented the same direction as the ends of the strands 116.

(31) Strand segment 120 is attached to strand couplings 118a and 118b, by any of the previously mentioned connecting methods. This approach requires connections at both strand couplings. However, it facilitates using different materials for strands 116 and for strand segments 120 if desired, and also allows attachment of the strand segments to a previously formed stent.

(32) FIG. 15 illustrates an alternative embodiment open-frame prosthesis 136, in which elongate strands 138 are wound about a mandrel to form multiple, generally hexagonal cells 140. As indicated in the enlargement, adjacent cells are joined by coextensive regions 142 along which strands 138 are twisted helically about one another. At a distal end 144 of the prosthesis, the strands are bent to provide loops 146. A plurality of radiopaque markers 148 are fixed to the loops.

(33) At a proximal end 150 of the prosthesis, pairs of strands 138 are welded together to form strand couplings. Each pair of adjacent couplings includes one strand with an extended portion shaped into a loop segment 152, which in turn is welded to the adjacent strand coupling of the pair. Radiopaque markers 153 are fixed near loop segments 152, and may be fixed to the loop segments. Strands 138 form multiple intersections 154 in addition to coextensive regions 142. Loop segments 152 can be arcuate as shown, or be shaped to more closely resemble loop segments 34-44.

(34) FIG. 16 shows a braided prosthesis 156 formed of two sets of oppositely directed helically wound strands 158. At both ends of prosthesis 156, pairs of the strands are welded or otherwise secured together to form proximal end strand couplings 160, and distal end strand couplings 162. The prosthesis includes a plurality of proximal end loop segments 164. Each loop segment 164 is connected to an associated pair of the strand couplings 160. Prosthesis 156 includes a plurality of distal end loop segments 166, each coupled to an associated pair of the distal end strand couplings.

(35) A salient feature of the present invention is that prostheses equipped with loop segments as previously described can be moved axially in either direction after they are deployed, with virtually no risk of trauma to surrounding tissue. FIG. 17 illustrates a proximal end region of prosthesis 156, and a positioning device 168 spaced apart proximally from the prosthesis. Device 168 includes an elongate flexible shaft 170, a distal portion of which is shown. A tine 172 at the distal end of shaft 170 extends away from the shaft, inclined proximally and radially outward. When shaft 170 is moved distally to position its distal end in proximate axial alignment with loop segments 164, the shaft is manipulated to direct tine 172 through one of the loops. Then the shaft is moved proximally to carry tine 172 into engagement with an associated loop segment 164, whereupon further proximal travel of the shaft pulls prosthesis 156 in the proximal direction.

(36) Initially, only the proximal region of prosthesis 156 may be pulled proximally, which causes localized axial elongation. The axial elongation radially contracts prosthesis 156 along its proximal end region near the loop segments. This facilitates proximal movement of the prosthesis by pulling the prosthesis radially inward at least slightly away from the surrounding tissue. As device 168 is moved further in the proximal direction, the frictional hold is overcome and the entire prosthesis moves proximally, although a distal portion of the prosthesis may remain engaged with surrounding tissue. This is beneficial, in that the frictional “drag” allows a more incremental, accurate adjustment of prosthesis position.

(37) For a symmetrical application of the pulling force, device 168 can be replaced with a device with several tines or shafts, to simultaneously pull several, or all, of the loop segments.

(38) According to another alternative, a tether can be threaded through loop segments 164, such that proximally pulling the tether brings the loop segments radially inward and closer together in cinch fashion.

(39) If desired, device 168 or the aforementioned tether can be used not only for incremental proximal adjustments, but for retrieval of prosthesis 156. To effect distal adjustments in the prosthesis position, a device similar to device 168, with a tine preferably inclined radially outwardly in the distal direction, could be used to engage one of distal end loop segments 166.

(40) While the present invention has been disclosed primarily in connection with self-expanding stents and other open frame prostheses of tubular construction, it is readily apparent that a balloon-expandable prosthesis, or any other bodily insertable device with free wire ends, can be modified with loop segments as described to reduce the risk of trauma to tissue. Also, while the preferred embodiments involve strand couplings formed by joining pairs of strands, such couplings can be formed with three or more strands, then connected in pairs to the loop segments.

(41) Thus, in accordance with the present invention, loop segments are attached to associated pairs of strand end couplings to reduce the risk of trauma to tissue, and provide a prosthesis that is radially compressible to a smaller diameter to facilitate intraluminal delivery. The looped ends eliminate the potential for adjacent twisted strand pairs to interlock when the prosthesis is compressed to its delivery state, ensuring a more reliable radial expansion of the prosthesis when deployed at the treatment site. The looped ends further facilitate incremental repositioning of the prosthesis after its deployment.