Study on calcium phosphate deposition on titanium surface in simulated body fluid

Titanium and its alloys have been extensively used for orthopedic and dental applications for their excellent mechanical and biological properties. However, the natural Ti and its alloys are not bioactive, thus numerous surface treatments have been proposed to improve their bioactivity. Commonly, the treated Ti surfaces were evaluated in simulated body fluid (SBF) to examine their calcium phosphate (Ca-P) induction ability, which is termed as bioactivity. However, there is still short of systematic investigations on Ca-P deposition in SBF for the treated Ti surface. Consequently there is lack of the Ca-P deposition mechanism study in simulated physiological environments. The present study aims to determining the Ca-P deposition mechanism and the critical factors for controlling Ca-P deposition in simulated body fluid, which favor us in understanding Ca-P formation on titanium surfaces in the physiological environment, and further in guiding the titanium implants design. Four kinds of single-step chemical treatments were performed, i.e. alkali treatment (AT), nitric acid treatment (NT), hydrogen peroxide treatment (HPT), and heat treatment at different temperature (H800, H600 and H400). The surface roughness, the surface chemistry and the surface energy effects on the Ca-P deposition were deliberately studied in the simulated body fluid. The results showed that the different surface roughness produced from the acid etching (AE) and mechanical polishing (MP) had no influence on the Ca-P induction ability. The chemical compositions, the OH, TiOH and titanium oxide phases did not show direct correlation with the Ca-P deposition either. The surface energy played a crucial factor on the calcium phosphate nucleation and growth in SBF, which was closely correlated with the Ca-P induction ability at the same roughness level; the larger of surface energy, the more favorable of the Ca-P deposition on the titanium surface. The calcium phosphate deposition mechanism was deduced from the heterogeneous nucleation and growth theory along with the surface charge interactions functionality analysis