Interaction of calcium and phosphate in apatite coating on titanium with serum albumin

A Ca-deficient carbonate apatite coating on titanium was prepared by pre-calcifying titanium in a saturated Ca(OH)2 solution and then immersing in a supersaturated calcium phosphate solution. The interaction of the protein with the apatite coating on titanium was investigated by scanning electron microscopy with X-ray energy dispersion spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. During immersion of the coating in bovine serum albumin (BSA) solution, accompanied by an adsorption of BSA onto the coating, calcium and phosphate ions dissolved and reprecipitated, resulting in the formation of the coating containing BSA from the surface to subsurface layers. The adsorption modified the structure and morphology of the apatite coating on titanium and changed the protein configuration. It was also found that the protein chemically adsorbed onto surfaces containing calcium or phosphorus, showed that both Ca and P on the apatite coating were the binding sites with protein. The BSA adsorption onto the coating involved several elements and groups. In this process, Ca played an essential role, and the interaction of Ca on the apatite coating with the protein stimulated the bond of the protein at P sites.