Improvement of bonding strength to titanium surface by sol-gel derived hybrid coating of hydroxyapatite and titania by sol-gel process

In this study, we investigated the hydroxyapatite(HA)/titania(TiO₂) hybrid coating on Ti substrate in order to combine advantages of both materials, namely the adhesion strength of TiO₂ on the substrate as well as the bioactivity of the HA. Composite sols of HA and TiO₂ were synthesized using calcium nitrate tetrahydrate and triethyl phosphite with various ratio. They were dropped onto cp Ti substrate and followed by spin-coating at 2000rpm for 10s. Then dried for 24h at room temperature and were heat-treated at 500°C for 2h. The crystalline phases, roughness and thickness of the coating films were measured by XRD, surface profiler, and SEM, respectively. The scratch test was performed as a criterion of adhesion strength between the coating film and the substrate. The critical load at which the coating film was peeled off completely from the substrate is determined using spherical diamond stylus. The bioactivity was observed after suspended in a simulated body fluid at 37°C. Effect of composition on the cell attachment onto the substrate was determined by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) method according to the amount of TiO₂ addition. Preosteoblast-like MG 63 cells were selected in this determination. According to increase the amount of TiO₂, the debonding strength of the hybrid coating film from Ti substrate was increased as well as the attachment density of MG 63 cells as expected. The debonding strength and the cell attachment density showed significant higher value than that of pure HA when the amount of TiO₂ was exceeded 30% and 50%, respectively (p < 0.05). These hybrid coating films were proved to be bioactive from the needle-shaped bone-like apatite formation after 2weeks of exposure to simulated body fluid.