Avoiding stress-induced martensitic transformation in nickel titanium alloys used in medical devices

• US 7,175,655 B1
• Filed: 09/17/2001
• Issued: 02/13/2007
• Est. Priority Date: 09/17/2001
• Status: Expired due to Term

• Current Assignee: Abbott Cardiovascular Systems Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: EndoVascular Technologies Incorporated (Boston Scientific Corporation)
• Inventors: Molaei, Masoud
• Primary Examiner(s): Bui; Vy Q.
• Application Number:
  US09/954,557
• Time in Patent Office: 1,975 Days
• Field of Search: 623 11- 15, 606/108, 606/191, 606/192, 606/194, 606/195, 606/198
• US Class Current: 623/1.18
• CPC Class Codes: A61F 2/86 Stents in a form characterised by the wire-like elements; Stents in the form characterised by a net-like or mesh-like structure
• CPC Class Codes: A61F 2210/0023 operated at different temperatures whilst inside or touching the human body, heated or cooled by external energy source or cold supply
• CPC Class Codes: C22F 1/006 Resulting in heat recoverable alloys with a memory effect

Abstract

A process for assembling a medical device made from a nickel-titanium alloy for use in a mammalian body while avoiding the formation of stress-induced martensite and a medical device used in combination with a delivery system for deployment into the mammalian body are disclosed. By heating the nickel-titanium alloy of the medical device to a temperature above M_d, and deforming and installing the device into a delivery system or holding capsule, it is possible to avoid the formation of stress-induced martensite in the stent, which stays in the austenitic phase throughout.

Claims

1. A medical device and delivery system, comprising:

a shape memory alloy element having a restrained shape, a deployed shape and an associated M_d temperature, the shape memory alloy element having been deformed at or above M_d into an at least partially deformed configuration; and

a hollow delivery system holding the at least partially deformed shape memory alloy element in an austenitic state in its restrained shape,

wherein the shape memory element self-expands into the deployed shape when not held by the delivery system.

2. The medical device and delivery system of claim 1, wherein the shape memory alloy includes nickel and titanium.

3. The medical device and delivery system of claim 1, wherein the medical device includes a stent.

4. The medical device and delivery system of claim 1, wherein the delivery system includes a catheter.

5. The medical device and delivery system of claim 1, wherein the shape memory alloy does not generate stress-induced martensite from being at least partially deformed into a restrained shape.

6. The medical device and delivery system of claim 1, further comprising a restraint configured to receive the shape memory alloy at a temperature at or above M_d, wherein the shape memory alloy is a tubular member with proximal and distal ends and the restraint is secured around the shape memory alloy in its deformed configuration.

7. The medical device and delivery system of claim 1, wherein the shape memory alloy is for use within a mammalian body or in close proximity to the mammalian body such that the device is at mammalian body temperature.

8. The medical device and delivery system of claim 7, wherein the mammalian body temperature is about 35 to 40 degrees C.

9. The medical device and delivery system of claim 1, wherein the shape memory alloy has an austenite start temperature (A_s), an austenite finish temperature (A_f), and a martensite deformation temperature (M_d).

10. The medical device and delivery system of claim 9, wherein the shape memory alloy includes the martensite deformation temperature (M_d) of about 50 degrees C. or more above the austenite finish temperature (A_f).

11. The medical device and delivery system of claim 9, wherein the shape memory alloy element self expands at a temperature above A_f and below M_d.

12. The medical device and delivery system of claim 1, wherein the shape memory alloy is in an austenitic state at room temperature of about 22 degrees C.