Preparation, biomimetic apatite induction and osteoblast proliferation test of TiO2-based coatings containing P with a graded structure

TiO2-based coatings containing P (T–P) were prepared on Ti6Al4V by microarc oxidation (MAO) with applied voltages of 200–400 V in an electrolyte containing (NaPO3)6 and NaOH. The surfaces of the T–P coatings became rough and the thickness increased with increasing the applied voltage. Above 200 V, anatase was found on the surface, and rutile was observed at 400 V. With increasing the coating thickness, the O and P concentrations increase; while Ti and Al concentrations decrease. Ti, O and P elements display a uniform distribution character around the micropores on the surface of the T–P coating formed at 300 V. However, the inner of the micropores exhibits a high Ti concentration and low O and P concentrations due to the graded distributions of Ti, O and P elements in the T–P coating. The apatite-forming ability of the T–P coating formed at 300 V was evaluated by immersing in a simulated body fluid (SBF) for 28 and 56 days. The results indicate that biomimetic apatite was formed on the surface of the T–P coating after immersion in SBF for 56 days. And the further cell experiment indicates that the T–P coating can provide surface suitable for the MG63 cell proliferation.