Material processing of hydroxyapatite and titanium alloy (HA/Ti) composite as implant materials using powder metallurgy: A review

The bio-active and biodegradable properties of hydroxyapatite (HA) make this material a preferred candidate for implants such as bone replacement in replacing natural tissues damaged by diseases and accidents. However, the low mechanical strength of HA hinders its application. Combining HA with a biocompatible material with a higher mechanical strength, such as a titanium (Ti) alloy, to form a composite has been of interest to researchers. A HA/Ti composite would possess characteristics essential to modern implant materials, such as bio-inertness, a low Young’s modulus, and high biocompatibility. However, there are issues in the material processing, such as the rheological behavior, stress-shielding, diffusion mechanism and compatibility between the two phases. This paper reviews the HA and Ti alloy interactions under various conditions, in vitro and in vivo tests for HA/Ti composites, and common powder metallurgy processes for HA/Ti composites (e.g., pressing and sintering, isostatic pressing, plasma spraying, and metal injection molding).