n-SiO2 Embedded HA/TiO2 Composite Coatings Deposited on Pure Titanium Substrate by Micro-Arc Oxidation

As orthopaedic and dental metallic implant materials, titanium and titanium alloys are widely used due to their relatively low modulus, good fracture toughness, excellent strenthto-weight ration, and superior biocompatibility and corrosion resistance (Long and Rack, 1998). They have become the first choice above all other candidate metallic implant materials such as Co-Cr-Mo alloys, stainless steel in recent years. But smooth titanium or titanium alloy implants are considered to have weak bioactivity and bone-bonding in vivo (Li et al., 2004; Sul, 2003; Xie et al., 2000). Therefore, a composite system including an hydroxyapatite (HA) film on the titanium or titanium alloy implant, which combines the mechanical benefits of metal alloys with the biological properties of HA, has generated widespread interest because of the HA has excellent biocompatibility and tissue bioactivity (Tkalcec et al., 2001; Weng et al., 1997). Many techniques including plasma-spraying, pulsed laser deposition and electrophoretic deposition have been studied to produce HA films over the last 20 years, and plasma-spraying was the only one that achieved commercial success (Yang et al., 2005; Cotell et al., 1992; ZHITOMIRSKY, 1997; Liu, et al., 2002; Wen et al., 2002; Gu et al., 2003; Clèries et al., 2000; Koike & Fujii, 2001). But the film formed by plasmaspraying was easily separated from the surfaces or resorbed in the body environment because of the unstable characteristics through its rapid solidification, inhomogeneous composition, melted and decomposed phases, etc (Xu et al., 2006). The other methods such as electrophoretic deposition may produce highly crystalline coatings, which are difficult to resorb in the body (Gross & Berndt, 1994). Recently, it was reported that hydroxyapatite-containing titania coating on titanium or titanium alloy was prepared by micro-arc oxidation (MAO) technique (Barrere et al., 2002; Chen et al., 2006; Fu et al., 2002; Han et al., 2003; Wei et al., 2009; Ni et al., 2008). The obtained coating has a porous surface and exhibits perfect biocompatibility and biological activity, which is essential for orthopaedic and dental metallic implant materials. This technique is very suitable for the bioactive surface modification of titanium and its alloy implants.