Calcium phosphate deposition on titanium surfaces in the presence of fibronectin

Abstract

Titanium implants are known to nucleate spontaneously a calcium phosphate (apatite-like) layer when in contact with biological model fluids. The presence of proteins either in solution or pre-adsorbed on the titanium surface may influence the process of calcium phosphate deposition. The role of fibronectin, a protein known to promote cell adhesion in spite of its low concentration in biological fluids, was dissolved in Hanks' balanced salt solution (HBSS) and investigated. Several techniques of surface analysis, namely wettability, XPS, and SEM studies, were applied. The concentration of fibronectin in the HBSS solution was an important parameter in the process of calcium phosphate deposition. Concentrations as low as 0.01 mg/mL did not significantly affect the ionic precipitation; however, if the protein concentration was increased to 0.05 mg/mL, a value still far below the concentration in blood (0.2 mg/mL), the formation of a calcium phosphate layer was strongly inhibited. The influence of fibronectin pre-adsorbed on titanium surface also was investigated. It was found, as in the first case, that the extent of ionic precipitation that occurred during the immersion in HBSS depended on the protein concentration in the NaCl solution used to pre-immerse the titanium sample.