Method for imparting improved fatigue strength to wire made of shape memory alloys, and medical devices made from such wire

• US 8,414,714 B2
• Filed: 10/31/2009
• Issued: 04/09/2013
• Est. Priority Date: 10/31/2008
• Status: Active Grant

• Current Assignee: W. L. Gore & Associates (W.L. Gore & Associates)
• Original Assignee: Fort Wayne Metals Research Products Corp. (Fort Wayne Metals, Inc.)
• Inventors: Schaffer, Jeremy E.
• Primary Examiner(s): WYSZOMIERSKI, GEORGE P
• Application Number:
  US12/610,297
• Publication Number:
  US 20100107628A1
• Time in Patent Office: 1,256 Days
• Field of Search: None
• US Class Current: 148/402
• CPC Class Codes: A61L 2400/16 Materials with shape-memory or superelastic properties
• CPC Class Codes: A61L 31/022 Metals or alloys
• CPC Class Codes: A61L 31/14 Materials characterised by their function or physical properties , e.g. injectable or lubricating compositions, shape-memory materials, surface modified materials
• CPC Class Codes: A61N 1/05 for implantation or insertion into the body, e.g. heart electrode A61N1/06 takes precedence
• CPC Class Codes: B21F 9/00 Straining wire straining prestressing wires for concrete E04G21/12; connections or attachments adapted for straining F16G11/00; bundling machines or tools B65B13/00
• CPC Class Codes: C22C 19/00 Alloys based on nickel or cobalt
• CPC Class Codes: C22C 19/007 with a light metal (alkali metal Li, Na, K, Rb, Cs; earth alkali metal Be, Mg, Ca, Sr, Ba, Al Ga, Ge, Ti) or B, Si, Zr, Hf, Sc, Y, lanthanides, actinides, as the next major constituent
• CPC Class Codes: C22F 1/006 Resulting in heat recoverable alloys with a memory effect

Abstract

Wire products, such as round and flat wire, strands, cables, and tubing, are made from a shape memory material in which inherent defects within the material are isolated from the bulk material phase of the material within one or more stabilized material phases, such that the wire product demonstrates improved fatigue resistance. In one application, a method of mechanical conditioning in accordance with the present disclosure isolates inherent defects in nickel-titanium or NiTi materials in fields of a secondary material phase that are resistant to crack initiation and/or propagation, such as a martensite phase, while the remainder of the surrounding defect-free material remains in a primary or parent material phase, such as an austenite phase, whereby the overall superelastic nature of the material is preserved.

Claims

1. A medical device comprising a wire made of a nickel-titanium shape memory material, a majority of the titanium shape memory material in an austenitic phase at a human body temperature, said wire having a fatigue endurance such that said wire survives 10⁶ cycles at a 1.90% peak-to-peak strain amplitude.

2. The medical device of claim 1, wherein said wire has a fatigue endurance such that said wire survives 10⁹ cycles at between a 1.90% peak-to-peak strain amplitude and a 2.2% peak-to-peak strain amplitude.

3. The medical device of claim 1, wherein said wire has a fatigue endurance such that said wire survives 10⁹ cycles at between a 1.90% peak-to-peak strain amplitude and a 2.2% peak-to-peak strain amplitude.

4. The medical device of claim 1, wherein said wire has a residual strain of less than 0.25% after being subjected to engineering strain of 9.5%.

5. The medical device of claim 1, wherein said wire has an isothermally non-recoverable strain of less than 1%.

6. The medical device of claim 1, wherein said wire has an isothermally non-recoverable strain of less than 0.35%.

7. The medical device of claim 1, wherein said wire has an isothermally non-recoverable strain of less than 0.25%.

8. The medical device of claim 1, wherein said wire has an isothermally non-recoverable strain of less than 0.20%.

9. The medical device of claim 1, wherein said wire has a circular cross-section.

10. The medical device of claim 1, wherein said wire has a non-circular cross-section.

11. The medical device of claim 1, wherein said wire comprises tubing.

12. The medical device of claim 1, wherein said wire has a fatigue endurance such that said wire survives 10⁹ cycles at a 1.90% peak-to-peak strain amplitude.

13. A medical device comprising a wire product made of a shape memory material, said shape memory material having a plurality of defects, said wire product substantially comprised of said shape memory material in a primary phase and including portions of said shape memory material comprising a plastically deformed secondary phase at localized regions disposed proximate respective said defects, with at least some of said secondary phase portions separated by said primary phase, wherein said wire has a residual strain of less than 0.25% after being subjected to engineering strain of at least 9.5%.

14. The medical device of claim 13, wherein said shape memory material is a nickel-titanium shape memory material, said primary phase is an austenite phase at a human body temperature such that said nickel-titanium shape memory material is adapted to exhibit superelastic characteristics in vivo, and said secondary phase portions comprise a martensite phase.

15. The medical device of claim 14, wherein said wire product has an isothermally non-recoverable strain of less than 1%.

16. The medical device of claim 14, wherein said wire product has an isothermally non-recoverable strain of less than 0.35%.

17. The medical device of claim 14, wherein said wire product has an isothermally non-recoverable strain of less than 0.25%.

18. The medical device of claim 14, wherein said wire product has an isothermally non-recoverable strain of less than 0.20%.

19. The medical device of claim 13, wherein said secondary phase portions together comprise less than 15% of the shape memory material, by volume.

20. The medical device of claim 13, wherein said shape memory material is a nickel-titanium shape memory material, and said wire product has a fatigue endurance such that said wire survives 10⁶ cycles at a 1.90% peak-to-peak strain amplitude.

21. The medical device of claim 13, wherein said shape memory material is a nickel-titanium shape memory material, and said wire product has a fatigue endurance such that said wire survives 10⁶ cycles at between a 1.90% peak-to-peak strain amplitude and a 2.2% peak-to-peak strain amplitude.

22. The medical device of claim 13, wherein said shape memory material is a nickel-titanium shape memory material, and said wire product has a fatigue endurance such that said wire survives 10⁹ cycles at between a 1.90% peak-to-peak strain amplitude and a 2.2% peak-to-peak strain amplitude.

23. The medical device of claim 13, wherein said wire product is selected from the group consisting of wire having a circular cross-section, wire having a non-circular cross-section, cable, coil, and tubing.

24. The medical device of claim 13, wherein said wire comprises tubing.

25. The medical device of claim 13, wherein said shape memory material is a nickel-titanium shape memory material, and said wire product has a fatigue endurance such that said wire survives 10⁹ cycles at a 1.90% peak-to-peak strain amplitude.