Formation Mechanism and Biological Properties of Different Structured HA/TiO2 Coatings on Titanium Prepared by Micro-Arc Oxidation

Abstract

In this paper, porous, flocculent and petal-structured hydroxyapatite (HA)/TiO2 composite coatings were prepared on titanium (Ti) surfaces by one-step micro-arc oxidation (MAO) to enhance the biological property, and the formation mechanism of the different coatings was investigated. The results showed that, compared with the porous and flocculent coatings which can be easily formed, the petal-structured HA/TiO2 coating can only be formed when Ca(COOH)2 concentration, current, voltage and time reached certain threshold values. At low current, the HA petals were large, the surface morphology, roughness and hydrophilicity were all affected by voltage and time. At high current, the petals tended to grow small and dense, however the surface morphology and roughness were less affected by voltage and time, only that the hydrophilicity was affected by voltage and time at low values within narrow ranges. All the prepared coatings had good combination with Ti substrate when the applied current was less than 0.8 A. Based on the results, the growth process model of the HA/TiO2 coatings was proposed. Compared with the flocculent and porous coatings, the petal-structured HA/TiO2 coating was more beneficial for MC3T3-E1 cells adhesion, spreading and proliferation, it also showed better bioactivity. The optimal performance can be obtained by controlling the Ca(COOH)2 concentration, current, voltage and time during MAO process. The improved biological property of the petal-structured HA/TiO2 was attributed to the suitable coating thickness, large surface roughness, highly exposed HA area and good hydrophilicity.