The influence of proteins on calcium phosphate deposition over titanium implants studied by dynamic contact angle analysis and XPS

The spontaneous formation of a calcium phosphate (apatite-like) layer on the surface of titanium implants in contact with biological model fluids is well known, but the effect of the presence of proteins in real biological fluids is not yet well understood. In this work, the process of calcium phosphate deposition on titanium surfaces immersed in Hanks' balanced salt solution (HBSS) containing dissolved bovine serum albumin (BSA) was studied by dynamic contact angle analysis (DCA) and X-ray photoelectron spectroscopy (XPS). Previous studies using electrochemical and wettability techniques as well as scanning electron microscopy (SEM) and XPS showed that although the deposition of calcium and phosphate ions still occurs in the presence of albumin, the growth of a calcium phosphate layer is inhibited. The present study suggests that when the Ti sample contacts a solution where both protein molecules and calcium and phosphate ions are present, the protein adsorbs first followed by the deposition of the ions. The same behaviour was observed for Ti substrates pre-covered by an apatite-like layer. Ti samples previously coated with a protein film, obtained by incubation in an isotonic saline solution of albumin, were studied after immersion in HBSS. In this case only XPS was able to detect traces of calcium and phosphate ions in the surface layer which were invisible to the DCA analysis. (C) 1997 Elsevier Science B.V.