Nucleation of biomimetic Ca-P coatings on ti6A14V from a SBF x 5 solution: influence of magnesium.

Biomimetic Calcium-Phosphate (Ca-P) coatings were applied by using 5 times concentrated Simulated Body Fluid (SBF x 5) using Carbon Dioxide gas. This process allows the deposition of a uniform Ca-P coating within 24 h. A previous study of our process emphasized the importance of hydrogenocarbonate ions (HCO-3), a crystal growth inhibitor. The aim of the present study was to investigate the role of the other crystal growth inhibitor present in SBF x 5, Magnesium (Mg2+), on the Ca-P coating formation. Several SBF x 5 solutions were prepared with various Mg2+ and HCO3 contents. No Ca-P deposits were detected on Ti6A14V substrate soaked for 24h in a Mg-free SBF x 5 solution, whereas by increasing HCO-3 content in a Mg-free SBF x 5 solution, a Ca-P coating developed on Ti6A14V substrate. Therefore, it appeared that Mg2+ has a stronger inhibitory effect on apatite crystal growth than HCO-3. Nevertheless, Mg2+ plays also another important role as suggested by depth profile X-ray Photoelectron Spectroscopy (XPS) of the Ca-P coating obtained from SBF x 5 solution. Ca2+ and Mg2+ contents increased significantly at the titanium/coating interface. Therefore, Ca2+ and Mg2+ initiated Ca-P coating from SBF x 5 solution. The relatively high interfacial concentration in Mg2+ favors heterogeneous nucleation of tiny Ca-P globules onto the substrate. So physical adhesion is enhanced at the early stage of the coating formation.