Fabrication and Surface Modification of Porous Nickel-Titanium Shape Memory Alloy for Bone Grafts, pp. 69-111
Authors: Shuilin Wu, Xiangmei Liu, Paul K. Chu, Tao Hu, Kelvin W. K. Yeung, and Jonathan C. Y. Chung
Abstract: Equiatomic porous nickel-titanium shape memory alloys (NiTi SMAs) are becoming one of the most promising biomaterials for bone grafts because of their unique advantages over currently used biomaterials. For example, they have good mechanical properties and lower Young‘s modulus relative to dense NiTi, Ti, and Ti-based alloys. Porous NiTi SMAs are relatively easy to machine compared to porous ceramics such as hydroxyapatite and calcium phosphate that tend to exhibit brittle failure. The porous structure with interconnecting open pores can also allow tissue in-growth and favors bone osseointegration. In addition, porous NiTi alloys possess good shape memory effect (SME) and superelasticity (SE) similar to dense NiTi alloys. In order to optimize porous NiTi SMAs used in bone grafts, current research focuses on the fabrication methods and surface modification techniques to obtain adjustable bone-like structures with good mechanical properties and excellent superelasticity as well as a bioactive passivation layer on the entire exposed surface to block nickel leaching and enhance the surface biological activity. This chapter describes the recent progress in the fabrication process and surface modification methods of porous NiTi SMAs and discusses subsequent effects of these processes and techniques on the materials properties from the perspective of bone grafts applications.