Molecular precursor method for thin calcium phosphate coating on titanium

Carbonate-containing hydroxyapatite was deposited onto titanium using a molecular precursor method, which is a novel technique for coating metal oxide film. The molecular precursor solution was prepared by the addition of dibutylammonium metaphosphate salt to an ethanol solution of Ca-ethylenediamine-N,N,N′,N′-tetraacetic acid/amine complex. The molecular precursor solution was applied to titanium and fired at different temperatures from 300 to 700 °C for 2 h using a furnace under ordinary atmospheric conditions. A firing temperature below 400 °C did not produce an apatite film on the titanium. Firing at 600 or 700 °C formed a crystalline carbonate-containing hydroxyapatite film on the titanium substrate. Thermal analysis confirmed that a firing temperature above 500 °C is necessary to form calcium phosphate films on titanium substrates. The coating thickness and Ca/P ratio determined by electron probe microanalysis were about 0.44±0.01 μm and 1.56±0.04, respectively. After immersion of coated specimens in phosphate buffered saline (PBS) solution for periods of 1 week and 1 month, the formation of slight cracks in the coated films was observed. The tensile bond strength measurement and scratch test showed an excellent degree of adhesion of the coated film on the titanium after the PBS immersion. Finally, we concluded that a firing temperature of 600 °C is suitable for producing an adherent carbonate-containing apatite film on titanium.