Shape memory, superelastic and low Young's modulus alloys

The conventional shape memory alloy, TiNi, is widely used in biomedical implants. TiNi is receiving particular attention owing to its usefulness in stents and guide wires for catheters. However, the Ni in TiNi poses a high risk of allergic reaction, and so Ni-free shape memory and superelastic titanium alloys are being developed. Titanium alloys with a low Young's modulus are also required to inhibit stress shielding between implant and bone, because stress shielding leads to bone atrophy and poor bone remodeling. Titanium alloys with adjustable Young's moduli are being developed in order to satisfy the requirements of both surgeons and patients. In this chapter, the fundamental characteristics of shape memory and superelastic alloys for biomedical applications are discussed. In addition, the effects of alloying elements on the shape memory, superelastic behavior, biocompatibility and corrosion resistance, and endurance of TiNi are described. Further, the fabrication of TiNi sheets is covered. Finally, the developments of a new alloy, low Young's modulus alloys, and the metals required for spinal surgery are discussed.