Effect of albumin and fibrinogen on calcium phosphate formation on sol-gel-derived titania coatings in vitro

The sol-gel technique provides a method to produce porous titania (TiO2) coatings, which are known to induce bone-like hydroxyapatite formation on their surface in vitro. In this study, the calcium phosphate formation (in vitro bioactivity) on a sol-gel-derived titania coating was investigated in vitro in a simulated body fluid in the presence and absence of albumin (BSA) and fibrinogen (Fib) in solution as well as the effect of surface immobilized proteins on the biomineralization process. The effect of proteins on calcium phosphate (CP) formation was followed by ion concentration analysis, XRD, SEM-EDX, and XPS. When BSA and Fib were present in solution, the CP layer growth kinetics were strongly retarded. It is suggested that the bone-like apatite formation on sol-gel-derived titania coatings occurs via continuous dissolution/reprecipitation processes, where the initially formed CP phase(s) recrystallizes into a more thermodynamically stable phase(s), as previously observed for other biomaterials. Inhomogeneous charging was observed in the XPS experiments, which could be used to distinguish between an amorphous CP layer and poorly crystalline CP regions.