Abstract

A novel method of fabricating TiNi superelastic microtubes with a dimension of less than 100 μm is presented in this chapter. The method was carried out by sputter-deposition of TiNi on a Cu-wire substrate, and after deposition the Cu wire was removed by etching to produce a tube hole. The shape-memory/superelastic behavior and fracture strength of the microtubes were characterized. The factors affecting the properties and a method to produce high-strength superelastic TiNi microtubes are discussed.

Introduction

Superelastic microtubes are attractive materials for application in the medical industry due to the increasing demands for less-invasive surgical devices, such as stents, catheters, microneedles, etc. Among many alloy systems that exhibits superelastic behavior, TiNi shape memory alloy is considered the most prominent due to its superior properties, such as large and stable superelastic strain [1, 2], excellent mechanical properties and relatively good biocompatibility [3]. Commercially available TiNi microtubes are usually processed by a tube-drawing method [4, 5, 6, 7, 8]. The available size of tubes that can be fabricated by tube drawing is limited to larger than 200 μm in outer-diameter and a wall thickness of 50 μm. A superelastic microtube with dimensions less than 200 μm has the potential to further miniaturize microdevices and thereby increasing their applicability.

A novel method to fabricate TiNi microtubes with dimensions less than 100 μm was suggested by utilizing a sputter-deposition method [9, 10]. The contents of this chapter are based on Ref. [9]. In this method a Cu-wire (diameter 50 μm) is used as a substrate and it was completely covered with TiNi by sputter-deposition. After deposition the Cu-wire was completely removed by etching to produce the tube hole.