Balloon expandable superelastic stent

1. A balloon expandable superelastic stent comprising a Ti—Ni—Nb shape memory alloy, wherein the content of Nb is at least 3 at %, the stent having been subjected to a shape memory treatment to have a reverse transformation finish temperature (Af point) which is (i) lower than a living body temperature in an unloaded state in which a strain has not been imposed on the shape memory alloy and (ii) higher than the living body temperature after the strain has been imposed on the shape memory alloy.

2. The balloon expandable superelastic stent according to claim 1 , wherein the stent is radially contracted and mounted to a balloon portion in a catheter to be guided to a diseased site,

wherein the stent recovers its shape by being warmed one of (i) simultaneously with balloon expansion and (ii) after the balloon expansion, and

wherein after recovering its shape the stent keeps shape recovery force even at the living body temperature.

3. The balloon expandable superelastic stent according to claim 2 , wherein the stent is obtained by one of: (i) forming a wire into a mesh pattern, and (ii) by processing a tube into a mesh pattern by laser machining of etching, and

wherein the stent having the mesh pattern is subjected to the shape memory treatment, then subjected to the strain, which is a strain of at least 8%, and then mounted to the catheter.

4. The balloon expandable superelastic stent according to claim 3 , wherein the strain is 10-15%.

5. The balloon expandable superelastic stent according to claim 2 , wherein the strain is a strain of at least 8% that is imposed by mechanical expansion of the stent, and the stent is mounted to the catheter after the strain is imposed.

6. The balloon expandable superelastic stent according to claim 2 , wherein the strain is a strain of at least 8% that is imposed by mechanical radial contraction of the stent, and the stent is mounted to the catheter after the strain is imposed.

7. The balloon expandable superelastic stent according to claim 1 , wherein the stent is obtained one of:

(i) by forming a wire into a mesh pattern, and (ii) by processing a tube into a mesh pattern by laser machining or etching, and

wherein the stent having the mesh pattern is subjected to the shape memory treatment and then subjected to the strain, which is a strain of at least 8%.

8. The balloon expandable superelastic stent according to claim 7 , wherein the strain is 10-15%.

9. The balloon expandable superelastic stent according to claim 1 , wherein the strain is a strain of at least 8% that is imposed by mechanical expansion of the stent.

10. The balloon expandable superelastic stent according to claim 1 , wherein the strain is a strain of at least 8% that is imposed by mechanical radial contraction of the stent.

11. The balloon expandable superelastic stent according to claim 1 , wherein the content of Nb is 6-9 at %.

12. A method of producing a balloon expandable superelastic stent, the method comprising:

slotting a tubular material of a Ti—Ni—Nb shape memory alloy in which the content of Nb is at least 3 at %;

expanding the tubular material in a radial direction;

subjecting the tubular material to shape memory treatment;

imposing a strain on the shape memory alloy, at a temperature that is not higher than a reverse transformation start temperature (As point) of the shape memory alloy; and

radially contracting the tubular material;

wherein (i) after the shape memory treatment but before the strain is imposed, the shape memory alloy has a reverse transformation finish temperature (Af point) that is lower than a living body temperature, and (ii) after the shape memory treatment and after the strain is imposed, the shape memory alloy has a reverse transformation finish temperature (Af point) that is higher than a living body temperature.

13. The method according to claim 12 , wherein the strain is a strain of at least 8%.

14. The method according to claim 13 , wherein the strain is 10-15%.

15. The method according to claim 12 , wherein the content of Nb is 6-9 at %.