Method of forming a bend of a predetermined bend angle in a shape memory alloy wire and method of making a self-expanding stent

1. A method of making a self-expanding stent, the method comprising:

applying a bend stress sufficient to over-bend a portion of a wire comprising a nickel-titanium alloy by an amount in a range from 85% to 105%, where the wire includes from about 40% to 46% cold work, and wherein a maximum amount of strain imparted to an outer surface of the wire during over-bending is about 30%;

releasing the bend stress, thereby forming a bend having a predetermined bend angle in the wire;

repeating the applying and releasing of the bend stress on successive portions of the wire, thereby creating a series of the bends along a length of the wire in a predetermined bend pattern, where the predetermined bend pattern is a zigzag pattern;

positioning the wire comprising the predetermined bend pattern about a mandrel in an expanded stent geometry, the positioning comprising forming the wire into a ring; securing ends of the wire together; and sliding the ring over the mandrel; and

after the positioning, heat setting the wire in the expanded stent geometry, thereby forming a self-expanding stent.

2. The method of claim 1 , wherein the positioning is carried out without applying any substantial tension to ends of the wire.

3. The method of claim 1 , wherein a plurality of the wires, each comprising the predetermined bend pattern, are positioned about the mandrel prior to heat setting.

4. The method of claim 1 , wherein the wire is not restrained on the mandrel during the heat setting.

5. The method of claim 1 , wherein the heat setting is carried out at a temperature in a range from about 300° C. to about 550° C.

6. The method of claim 5 , wherein the heat setting takes place in a fluidized bed.

7. The method of claim 1 , wherein the applying and the releasing of the bend stress is carried out automatically using a programmable wire bending apparatus.

8. The method of claim 1 , wherein each of the bends in the predetermined bend pattern comprises an included angle in a range from about 10° to about 150°.

9. The method of claim 1 , wherein the mandrel does not include radially projecting pins.

10. The method of claim 1 , wherein the mandrel has a circular transverse cross-section with a diameter in a range from about 4 mm to about 46 mm.

11. The method of claim 1 , wherein the wire comprises a near-equiatom nickel-titanium alloy comprising an atomic ratio of nickel to titanium in a range from 45:55 to 55:45.

12. The method of claim 1 , wherein the wire has a core-shell structure with a shell radially surrounding an elongated core, and wherein the core or the shell comprises the nickel-titanium alloy.

13. The method of claim 1 , further comprising, after forming the self-expanding stent, attaching a graft material thereto, thereby forming a stent graft.

14. A method of forming a bend of a predetermined bend angle in a shape memory alloy wire, the method comprising:

applying a bend stress sufficient to over-bend a portion of a wire comprising a nickel-titanium alloy by an amount ranging from 85% to 105%, where the wire includes from about 40% to 46% cold work, and wherein a maximum amount of nonrecoverable strain imparted to an outer surface of the wire during over-bending is about 30%; and

releasing the bend stress, thereby forming a bend having a predetermined bend angle in the wire;

repeating the applying and releasing of the bend stress on successive portions of the wire, thereby creating a series of the bends along a length of the wire in a predetermined bend pattern, where the predetermined bend pattern is a zigzag pattern;

positioning the wire comprising the predetermined bend pattern about a mandrel in an expanded stent geometry, wherein the positioning is carried out without applying tension to ends of the wire; and

after the positioning, heat setting the wire in the expanded stent geometry, thereby forming a self-expanding stent.