Effect of Hydrothermal Self-Healing and Intermediate Strengthening Layers on Adhesion Reinforcement of Plasma-Sprayed Hydroxyapatite Coatings

Abstract

Biomaterials employed in calcified hard tissue repair generally serve the purpose of load carrying in cases of fractures, defects and joint replacement. Metallic materials are more suitable for load-bearing applications compared with ceramics and polymeric materials due to their combination of high mechanical strength and fracture toughness. Among generally used metallic biomaterials such as 316L stainless steel and Co-Cr-Mo alloys (ASTM F75), grade II commercial pure titanium (ASTM F67) and Ti-6Al-4V alloys (ASTM F136ELI) exhibit the most suitable characteristics for biomedical applications because of their high biocompatibility, specific strength and corrosion resistance [Niinomi, 2001]. The apparent success of titanium and its alloys in implants has been attributed to the existence of a thin, stable passivation TiO2 layer. Another advantage of titanium and its alloys for using in hard tissue replacements is their low Young’s modulus because a low Young’s modulus equivalent to that of human cortical bone is simultaneously required to inhibit stress shielding effect and bone absorption [Pilliar et al., 1979; Kuroda et al., 1998; Niinomi et al., 2002]. Nowadays, they are commonly clinical used in hard tissue implants such as artificial hip prosthesis, knee joints and dental roots. A biological fixation between these hard tissue implants and surrounding bones can be successfully achieved by the bone ingrowth with a mechanical interlocking [Engh et al., 1987; Callaghan, 1993]. However, limitations of metallic biomaterials are the release of toxic metallic ions and corrosion/wear products into surrounding tissues and fluids [Sunderman et al., 1989; Healy & Ducheyne, 1992; Niinomi et al., 1999; Akahori et al., 2004].