Hydroxyapatite Formation on Titanium by Microarc Oxidation and Hydrothermal Treatment

Objectives: This study was purposed to investigate the effects of applied electric conditions and types of hydrothermal solutions on the formation of highly dense and well crystallized hydroxyapatite-containing titanium oxide films while using AC-mode microarc oxidation(MAO) and hydrothermal treatment. Methods: MAO groups were fabricated by MAO treatment of titanium (CP-Ti; ASTM grade 2) under different voltages (150, 175, and 200 V) and frequencies (200, 350, and 500 Hz) of AC type-rectangular electric pulses in electrolyte solution containing 0.2 M calcium acetate monohydrate and 0.02 M β-glycerophosphoric acid (β-GP). In order to form HAp, MAO-treated groups were hydrothermally treated in water (HT groups) or 0.002 M β-GP (HTP groups) adjusted to pH 11.5. Surface characteristics of the fabricated samples were evaluated using FE-SEM, EDX, XRD, and Raman spectrometer. The distribution of HAp particles on the surface of HTP group samples was evaluated using laser confocal scanning microscope (LCSM). Results: MAO group fabricated under high frequency condition showed a surface with evenly distributed pores. The density of pores increased as the voltage and frequency increased. The Ca/P ratios of MAO groups were higher than that of HAp. The oxide layer formed by MAO treatment was consisted of CaTiO₃ (CTO) and TiO₂. As the AC frequency increased, anatase TiO₂ structure formed dominantly with correspondingly reduced amount of CTO. By hydrothermal treatments, HTP groups showed more densely formed HAp particles on their surfaces compared with HT groups. Among HTP groups, those samples fabricated under high frequency electric conditions showed more evenly distributed HAp particles on their surfaces. Conclusion: We could fabricate the oxide layer containing more evenly and densely distributed crystalline HAp particles on CP-Ti using MAO treatment followed by hydrothermal treatment by changing electric conditions and hydrothermal solutions. This work was supported by the Korea Research Foundation Grant (KRF-2004-041-E00300).