Titanium-niobium-hafnium alloy shape memory wire
View Patent ↗Ti—Nb—Hf/Zr—(Cr) alloy shape-memory wires are provided which are suitable for use in medical devices and actuators, and methods for manufacturing such wires are provided. The present shape-memory Ti—Nb—Hf/Zr—(Cr) alloy is a superelastic wire material particularly suited for in vivo applications. For example, the present Ti—Nb—Hf/Zr—(Cr) alloy wire is radiopaque, thereby enabling surgical use of a monolithic, shape-memory alloy wire while preserving the ability to monitor the in vivo location of the wire through X-ray or other radiation-based imaging systems. In addition, the present Ti—Nb—Hf/Zr—(Cr) alloy can be manufactured to exhibit shape-memory alloy material properties without the use of nickel as an alloy constituent, thereby accommodating nickel-sensitive patients. The present Ti—Nb—Hf/Zr—(Cr) alloy can also be processed to exhibit a martensite/austenite transformation temperature near body-temperature, i.e., 37° C., so that shape-memory effects can be utilized to accomplish work in vivo.
1. A shape-memory wire for a medical device, the wire comprising:
between 15 wt. % and 24.8 wt. % niobium;
between 24 wt. % and 31 wt. % hafnium, zirconium, or a combination thereof;
between 40 wt. % and 50 wt. % titanium; and
between 0.4 wt. % and 0.6 wt. % chromium,
the wire exhibiting superelastic behavior and having an austenitic finish temperature less than 37° C.
2. The shape-memory wire of claim 1 , in combination with a medical device incorporating said shape-memory wire.
3. The combination of claim 2 , wherein said medical device comprises one of a stent, a guidewire, an aneurysm occlusion device, a heart wall closure device, an orthodontic wire, and a surgical anchoring device.
4. The shape-memory wire of claim 1 , wherein the wire comprises a drawn wire construct.
5. The shape-memory wire of claim 4 , wherein the drawn wire construct comprises a round wire defining an outer diameter and an axial length.
6. The shape-memory wire of claim 1 , wherein the wire has a diameter less than 10 mm.
7. The shape-memory wire of claim 1 , wherein the wire comprises said niobium, said hafnium, zirconium, or a combination thereof and balance of said titanium.
8. The shape-memory wire of claim 1 , wherein the wire has a modulus of elasticity between 50 GPa and 80 GPa.
9. The shape-memory wire of claim 1 , wherein the wire exhibits a total isothermally recoverable strain of between 2% and 4% at 310K.
10. The shape-memory wire of claim 1 , wherein the wire exhibits a fatigue life such that the wire survives 4×10 6 cycles at a strain amplitude of 0.8%.
11. The shape-memory wire of claim 1 , wherein the wire exhibits a fatigue life such that the wire survives 2×10 5 cycles at a strain amplitude of 1.0%.
12. The shape-memory wire of claim 1 , wherein the wire exhibits a fatigue life such that the wire survives 10 4 cycles at a strain amplitude of 1.2%.
13. The shape-memory wire of claim 1 , wherein the wire comprises a flat material.
14. The shape-memory wire of claim 1 , wherein the wire comprises a hollow tube material.
15. The shape-memory wire of claim 1 , wherein the wire comprises a rod material having a diameter of less than 5 mm.
16. The shape-memory wire of claim 1 , wherein the wire comprises a continuous wire wound onto a spool.
17. The shape-memory wire of claim 1 , wherein the wire does not include nickel as an alloy constituent.
18. The shape-memory wire of claim 1 , wherein the wire is nickel-free.
19. A method for producing a shape-memory wire for a medical device, the method comprising:
imparting between 50% and 99% cold work to a wire including:
between 40 wt. % and 50 wt. % titanium,
between 15 wt. % and 24.8 wt. % niobium,
between 24 wt. % and 31 wt. % hafnium, zirconium or a combination thereof, and
between 0.4 wt. % and 0.6 wt. % chromium, such that a resulting cold worked wire construct has a final diameter of less than 10 mm; and
shape-setting the cold-worked wire construct by annealing the cold worked wire construct at a time and temperature sufficient to restore a majority of the wire material to the parent material phase, the shape-setting step performed while a stress is applied to the wire construct, the cold-worked wire construct exhibiting superelastic behavior and having an austenitic finish temperature less than 37° C.
20. The method of claim 19 , further comprising, after the step of shape-setting, incorporating the shape-set wire construct into the medical device.
21. The method of claim 20 , wherein the medical device is one of a stent, a guidewire, an aneurysm occlusion device, a heart wall closure device, an orthodontic wire, and a surgical anchoring device.
22. The method of claim 19 , wherein the stress applied to the wire construct is a tension force sufficient to hold the wire in a substantially linear configuration.
23. The method of claim 19 , wherein the stress applied to the wire construct is a constraint of the wire construct in a specific non-linear shape to effect a final desired geometry.