Shape memory alloy articles with improved fatigue performance and methods therefor

• US 8,216,396 B2
• Filed: 08/31/2010
• Issued: 07/10/2012
• Est. Priority Date: 05/02/2003
• Status: Active Grant

• Current Assignee: W. L. Gore & Associates (W.L. Gore & Associates)
• Original Assignee: W. L. Gore & Associates (W.L. Gore & Associates)
• Inventors: Dooley, Bret A., Lasley, Christopher C., Mitchell, Michael R., Steele, Robert R., Tittelbaugh, Eric M.
• Primary Examiner(s): Wyszomierski, George
• Application Number:
  US12/873,191
• Publication Number:
  US 20100331946A1
• Time in Patent Office: 679 Days
• Field of Search: 148/402
• US Class Current: 148/402
• CPC Class Codes: A61B 2017/00867 shape memory effect for prostheses A61F2210/0014
• CPC Class Codes: A61C 2201/007 using shape memory effect
• CPC Class Codes: A61F 2/82 Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents stent-grafts for tubular structures of the body other than blood vessels A61F2/04; stent-grafts for blood vessels A61F2/07; instruments specially adapted for placement or removal of stents or stent-grafts A61F2/95; for closing wounds, or holding wounds closed A61B17/04 - A61B17/115; dilators A61M29/00
• 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 31/121 having an inorganic matrix
• 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: C22F 1/006 Resulting in heat recoverable alloys with a memory effect

Abstract

Articles made of shape memory alloys having improved fatigue performance and to methods of treating articles formed from shape memory alloy materials by pre-straining the articles (or desired portions of the articles) in a controlled manner so that the resultant articles exhibit improved fatigue performance. The shape memory articles are preferably medical devices, more preferably implantable medical devices. They are most preferably devices of nitinol shape memory alloy, most particularly that is superelastic at normal body temperature. The pre-straining method of the present invention as performed on such articles includes the controlled introduction of non-recoverable tensile strains greater than about 0.20% at the surface of a desired portion of a shape memory alloy article. Controlled pre-straining operations are performed on the shape-set nitinol metal to achieve non-recoverable tensile strain greater than about 0.20% at or near the surface of selected regions in the nitinol metal article. The pre-straining operations result in a significant increase in fatigue life of the selectively treated regions and an overall improvement in the fatigue performance of the device.

Claims

1. A self-expanding stent comprising a frame formed from nitinol exhibiting superelastic behavior at body temperature, the frame being configured to self-expand from a constrained delivery profile to an expanded operative profile, wherein the frame is pre-strained by the application of a pre-straining bending force to an extent that selectively induces at least about 8.0% tensile strain at or near only a surface of at least one selected location on the frame during circumferential compaction of the frame to a smaller size, wherein following release of the pre-straining force, the frame returns to, or near to, its geometry prior to the application of the pre-straining force.

2. A self-expanding stent according to claim 1 wherein the pre-straining results in at least about 8.5% tensile strain.

3. A self-expanding stent according to claim 1 wherein the stent is a stent-graft.

4. A self-expanding stent according to claim 2 wherein the stent is a stent-graft.

5. A self-expanding filter device comprising a frame formed from nitinol exhibiting superelastic behavior at body temperature, the frame being configured to self-expand from a constrained delivery profile to an expanded operative profile, wherein the frame is pre-strained by the application of a pre-straining bending force to an extent that selectively induces at least about 8.0% tensile strain at or near only a surface of at least one selected location on the frame during circumferential compaction of the frame to a smaller size, wherein following release of the pre-straining force, the frame returns to, or near to, its geometry prior to the application of the pre-straining force.

6. A self-expanding filter device according to claim 5 wherein the pre-straining results in at least about 8.5% tensile strain.