Thermoelastic and superelastic Ni-Ti-W alloy
A radiopaque nitinol stent for implantation in a body lumen is disclosed. The stent is made from a superelastic alloy such as nickel-titanium or nitinol, and includes a ternary element including tungsten. The added tungsten in specified amounts improve the radiopacity of the nitinol stent comparable to that of a stainless steel stent of the same strut pattern coated with a thin layer of gold. Furthermore, the nitinol stent has improved radiopacity yet retains its superelastic and shape memory behavior and further maintains a thin strut/wall thickness for high flexibility.
1. Radiopaque tubing, comprising:
a tubular-shaped body wherein the body includes a nickel-titanium superelastic alloy with a ternary element including tungsten, wherein the nickel-titanium superelastic alloy includes:
30 to 52 atomic percent titanium,
5 to 12 atomic percent tungsten, and
a balance of nickel;
wherein the tubular-shaped body is formed from a nickel-titanium-tungsten tubing having an austenite finish temperature (A f ) of −15° to 0° C., wherein the body is radiopaque.
2. The radiopaque tubing of claim 1 , wherein the nickel-titanium superelastic alloy includes 50.8 atomic percent nickel, 10 atomic percent tungsten, and a balance of titanium.
3. The radiopaque tubing of claim 1 , wherein the tubing includes a strut pattern with struts no greater than 0.0046 inch in width.
4. The radiopaque tubing of claim 1 , wherein the superelastic alloy includes a stress-induced martensite phase.
5. The radiopaque tubing of claim 3 , wherein an austenite finish temperature (A f ) of the superelastic alloy in the tubing with a stent strut pattern formed therein is greater than or equal to zero and less than or equal to 30 degrees C.
6. A superelastic, radiopaque metallic tubing for medical applications, comprising:
a tubular-shaped body including:
an atomic percent of nickel of 50.8,
an atomic percent of tungsten greater than or equal to 5 and less than or equal to 12, and
a balance of titanium;
wherein the tubular-shaped body has an active austenite finish temperature A f defined by −15° C.≦active A f ≦0° C.
7. The superelastic, radiopaque metallic tubing of claim 6 , wherein the tubular-shaped body includes 50.8 atomic percent nickel, 10 atomic percent tungsten, and a balance of titanium.
8. The superelastic, radiopaque metallic tubing of claim 6 , wherein the tubing includes a strut pattern having struts and each strut has a cross-sectional area of less than 0.000021 in 2 .
9. The superelastic, radiopaque metallic tubing of claim 6 , wherein the tubular-shaped body has been processed by melting nickel, titanium, and tungsten and cooling to the melt to form an alloy ingot, hot rolling the alloy ingot, cold and hot forming the alloy ingot into a cylinder, drilling the cylinder to form tubing, cold and hot drawing the tubing, and annealing the tubing.
10. Radiopaque tubing for medical applications, comprising:
a tubular body having an austenite finish temperature of −15° C. to 0° C.; and
wherein the tubular body includes 5 to 12 atomic percent tungsten, 50.8 atomic percent of nickel, and a balance of titanium such that the tubular body is radiopaque, having a radiopacity comparable to a stainless steel tubing having a thin coating of gold.
11. The radiopaque tubing of claim 10 , wherein the tubular body includes 10 atomic percent tungsten.
12. The radiopaque tubing of claim 10 , wherein the strut pattern provides a ratio of open area to metal of approximately 80 percent.