Coiled ladder stent
A coiled ladder stent comprises first and second rails and rungs connecting the rails. At least one rung has lower strength portion or is an enhanced flexibility rung, or both. The lower strength portion is positioned at a reduced strength fracture location along the rung so to promote any fracture of the ladder stent at the fracture location along the rung to help prevent fracture of a rail. One way to make the lower strength portion is to make the cross-sectional area of the lower strength portion less than the average cross-sectional area of the rung. The enhanced flexibility aspect helps to accommodate relative movement between the first and second rails. Doing so helps to prevent fracture of the rails and rungs. In some embodiments of the invention the enhanced flexibility rung comprises one or more nonlinear, such as generally S-shaped or generally U-shaped, portions.
1 . A coiled ladder stent comprising:
first and second rails;
rungs connecting the rails; and
at least a first rung comprising a lower strength portion, said lower strength portion positioned at a reduced strength fracture location along the first rung so to promote any fracture of the ladder stent at the fracture location to help prevent fracture of a rail.
2 . The ladder stent according to claim 1 wherein a plurality of said rungs comprises lower strength portions.
3 . The ladder stent according to claim 1 wherein said fracture location is centrally located along said first rung so to help reduce any negative consequences of any fracture of the first rung.
4 . The ladder stent according to claim 1 wherein said first rung has an average cross-sectional area and the lower strength portion has a reduced cross-sectional area relative to the average cross-sectional area.
5 . The ladder stent according to claim 1 wherein the rails have end portions and have central portions oriented parallel to one another.
6 . The ladder stent according to claim 1 wherein the rungs are oriented at acute angles to the rails.
7 . A coiled ladder stent comprising:
first and second rails;
rungs connecting the rails;
each of a plurality of said rungs comprising a lower strength portion, said lower strength portion positioned at a reduced strength fracture location along each of the plurality of said rungs so to promote any fracture of the ladder stent at the fracture location to help prevent fracture of a rail;
said fracture location being centrally located along each of the plurality of said rungs so to help reduce any negative consequences of any fracture any of the plurality of said rungs; and
each of the plurality of said rungs having an average cross-sectional area and the lower strength portion of each of the plurality of said rungs having a reduced cross-sectional area relative to the average cross-sectional area.
8 . A coiled ladder stent comprising:
first and second rails;
rungs connecting the rails; and
at least a first rung comprising an enhanced flexibility rung, the enhanced flexibility rung helping to accommodate relative movement between the first and second rails.
9 . The ladder stent according to claim 8 morning wherein the enhanced flexibility rung comprises a plurality of nonlinear portions.
10 . The ladder stent according to claim 8 wherein the enhanced flexibility rung comprises a nonlinear portion.
11 . The ladder stent according to claim 10 wherein the nonlinear portion comprises a curved portion.
12 . The ladder stent according to claim 10 wherein the nonlinear portion comprises a generally S-shaped portion.
13 . The ladder stent according to claim 10 wherein the nonlinear portion comprises a generally U-shaped portion.
14 . The ladder stent according to claim 10 wherein the nonlinear portion comprises a generally V-shaped portion.
15 . The ladder stent according to claim 8 wherein the enhanced flexibility rung comprises a portion having an opening formed therethrough.
16 . The ladder stent according to claim 15 wherein first rung has a length and the opening extends along the length.
17 . The ladder stent according to claim 8 wherein the rails have end portions and have central portions oriented parallel to one another.
18 . The ladder stent according to claim 8 wherein the rungs are oriented at acute angles to the rails.
19 . A coiled ladder stent comprising:
first and second rails;
rungs connecting the rails;
each of at least some of said rungs comprising an enhanced flexibility rung, the enhanced flexibility rung helping to accommodate relative movement between the first and second rails;
each of a plurality of said rungs comprising a lower strength portion, said lower strength portion positioned at a reduced strength fracture location along each of the plurality of said rungs so to promote any fracture of the ladder stent at the fracture location to help prevent fracture of a rail;
said fracture location being centrally located along each of the plurality of said rungs so to help reduce any negative consequences of any fracture any of the plurality of said rungs; and
each of the plurality of said rungs having an average cross-sectional area and the lower strength portion of each of the plurality of said rungs having a reduced cross-sectional area relative to the average cross-sectional area.