Multi-property nitinol by heart treatment

Abstract

Medical devices may be made of shape-memory materials portions of which have been heat treated to exhibit spatial variations in the stiffness of the material. Devices including stents, vena cava filters and guidewires may be constructed from such materials. Devices may also be made from shape-memory materials which have been locally heat treated such that the superelasticity of the treated portion is destroyed while the remainder of the shape-memory material can transition between the martensitic and austenitic states.

Description

BACKGROUND OF THE INVENTION [0001] The present invention is related to the use of shape memory materials in medical devices. [0002] A shape memory material can assume an initial high temperature configuration and a deformed low temperature configuration and revert back to the initial high temperature configuration upon the application of heat. The high temperature configuration of the material is set into the material or memorized during an initial shaping step in which the material is maintained at a high temperature in a desired shape for a period of time. [0003] This shape memory exhibited by metals results from the metal undergoing a reversible solid state phase transition. Specifically, the metal transitions from an austenitic state to a martensitic state with a decrease in temperature. The temperature at which the transition begins is typically designated Ms (martensite start temperature) while the temperature at which the transition finishes is designated Mf (martensite finis...

AI Technical Summary

Benefits of technology

[0011] The present invention is directed to medical devices which use shape-memory materials that have been differentially heat treated to exhibit spatially varying properties such as elasticity and stiffness.

[0019] In another embodiment, the invention is directed to a medical guidewire having been formed at least in part of a shape-memory metal. Different portions of the shape-memory metal have been treated differently to have different shape-memory properties. Desirably, at least one portion of the guidewire is subjected to a local heat treatment resulting in a reduced stiffness compared with the remainder of the guidewire. In this way, a guidewire of desired flexibility can be prepared. Via the localized heat treatment, a guidewire may be prepared in which at least a portion thereof retains its shape memory properties while a portion thereof loses its shape memory properties.

Problems solved by technology

Desirably, the local treatment will destroy the superelastic properties of the locally treated region.

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