Chemical Deposition Of Hydroxyapatite On The Surface Of Ti And NiTi

Titanium (Ti) and nickel-titanium shape memory alloy (NiTi) are proven to be very suitable materials for bioimplant applications. Hydroxyapatite (HA) coating can enhance the bioactivity and osteoconductivity of the Ti and NiTi substrate. In this paper, HA was coated onto Ti and NiTi substrates with the insertion of titania (TiO₂) buffer layer in order to improve the bonding strength between the HA layer and metal substrate, HA was coated onto the TiO₂ buffer layer by the chemical deposition method with relatively low temperature. The preparation method and technology of TiO₂ coating, and effect of heat-treated temperature on structure of TiO₂ film were systemically investigated in this paper, and the effect of different structure of TiO₂ film on the process of chemical deposition was compared.TiO₂ film was prepared on Ti by electroplating method. The coating was heat-treated in air at 300℃, 500℃, and 700℃, the heat-treated Ti was subsequently immersed in a super saturation calcify solution for 24h in order to deposit the HA onto the surface of Ti. TiO₂ coated Ti sample was heat-treated at 500℃, and then the sample immersed into a super saturation calcify solution for 24h. A uniform and dense deposition was formed on its surface. The deposition could cover the entire surface of substrate. The deposition layer can't be formed on the surface of Ti substrate heat-treated at 300℃and 700℃and immersed in a super saturation calcify solution for 24h. The TiO₂ coated NiTi sample heat-treated at 500℃was immersed in a super saturation calcify solution for 24h. There is no deposition formed on its surface.TiO₂ coating was prepared on Ti and NiTi alloy by sol-gel method. The coating was heat-treated in air respectively at 300℃, 500℃and 700℃. A uniform and dense coating was formed after the samples heat-treated at 500℃was immersed into super saturation calcify solution for 24h. There is no deposition formed for the samples heat-treated at 300℃and 700℃after they were immersed in a super saturation calcify solution for 24h.X-Ray diffraction results indicate that the structure of TiO₂ coating, formed by electroplating method on the Ti substrate is brookite while heat-treaded at 300℃. Itchanges into anatase phase while the sample heat-treated at 500℃and the phase consists of anatase and rutile while heat-treaded at 700℃. The structure of TiO₂ coating formed by electroplating method on the NiTi substrate is rutile while the sample heat-treaded at 500℃. The structure of TiO₂ coating heat-treaded at 500℃, prepared on Ti and NiTi substrate by sol-gel method, is rutile. Our results showed that the anatase phase of TiO₂ has the best induction effect for the deposition formation.NiTi alloy was pre-treated by a two-step chemical method, and then it was immersed in a super saturation calcify solution for 3 days. A uniform and dense deposition was produced. It is performed at relatively low temperature.Scanning electron microscopy results indicate that the microcrystal structure of deposition layer is similar regardless of preparation method of TiO₂ coating. The thickness of the deposition layer is approximately 25μm. The thickness of the HA crystal is approximately 0.1μm. The surface coating assumes porous which covers the specimen surface evenly. The X-Ray diffraction results indicate that deposition coated onto Ti and NiTi by the chemical deposition method is mainly composed of HA.