Hypoxia-mimicking Co doped TiO2 microporous coating on titanium with enhanced angiogenic and osteogenic activities.

UNLABELLED: Advanced titanium (Ti) based bone implant with both angiogenesis and osteogenesis stimulating activities for enhanced clinical performance is stringently needed. In the present work, TiO2/calcium-phosphate (TCP) coatings on Ti doped with cobalt (Co) of various amounts (designated as C2-TCP, C7-TCP, and C13-TCP where the Arabic numbers indicate the mean Co contents) are developed by a simple micro-arc oxidation procedure. The Co doped TCP coatings possess a microporous structure (pore size of 3-4μm in average diameter) which is evenly covered by nano-grains of 30-60nm in size. Successful Co incorporation in TCP is determined by X-ray photoelectron spectroscopy. The microstructure, TiO2 phase compositions, surface roughness, and wettability of TCP are not apparently affected by the Co incorporation. The Co doped coatings bond firmly to the Ti substrate and show good long-term adhesion strength stability in biological environment. Then the behaviors of rat bone marrow stem cells (MSCs) on the Co-incorporated TCP are evaluated. The Co incorporation leads to enhanced expression of the markers for both angiogenesis and osteogenesis, and the effects are positively related to the incorporated Co amount. Overdose of Co incorporation (C13-TCP) can induce certain cytotoxicity and an optimal dose of Co incorporation is essential to get the enhanced angiogenic and osteogenic activities without showing cytotoxicity. Between C2-TCP and C7-TCP that show no significant cytotoxicity, C7-TCP exhibits higher angiogenic and osteogenic activities. In conclusion, the Co doping is feasible to enhance the angiogenic and osteogenic activities of orthopedic and dental Ti implants for potentially improved clinical performance. STATEMENT OF SIGNIFICANCE: TiO2/calcium-phosphate coatings on Ti doped with cobalt are developed by a simple micro-arc oxidation procedure. The Co doped coatings bond firmly to the Ti substrate and show good long-term adhesion strength stability in biological environment. Furthermore, the cobalt doping is feasible to enhance the angiogenic and osteogenic activities of orthopedic and dental Ti implants for potentially improved clinical performance.