| Titanium and its alloys, due to the excellent mechanical properties, are widely used as biomedical implant materials. However, their bioactivity is not good.Therefore the preparation of HA coating with good biocompatibility and bioactivity on titanium or its alloys has become one of the research emphases recently.In order to improve the bonding strength between HA coating and Ti substrate, well ordered and uniform titanium oxide nanotube arrays were fabricated on the surface of titanium substrate by anodic oxidation in 0.5MH3PO4+0.138MNaF solution. Then the dicalcium phosphate dihydrate coatings(CaHPO4·2H2O, DCPD), electrodeposited on the anodized surface of Ti, were converted to hydroxyapatite coatings in alkaline solution.The bioactivity of the hydroxyapatite coating was studied by immersing the coatings in simulated body fluid(SBF) and citric acid-containing phosphate buffer solutions(CPBS) respectively. Moreover, the biological safety of the hydroxyapatite coating was evaluated in vitro by the hemolytic test and the acute systematic toxicity test. Furthermore, the morphology of titanium oxide nanotubes and the coatings was observed by means of scanning electron microscope(SEM). The composition and the structure of the coatings were analyzed by X-ray diffractometer(XRD) and ( Fourier transform infrared spectroscopy)FTIR. Meanwhile, the bonding strength of the interface between the HA coatings and the substrate was detected.It was demonstrated that the hydroxyapatite coatings were deposited in the nozzle of the nanotubes and/or between the nanotubes. The results of the immersion test in SBF and CPBS showed that the coatings possessed a good bioactivity in SBF, and were less soluble in CPBS. And no obvious whole body toxicity reaction and no haemolytic phenomenon were observed. The bonding strength of the interface between the HA coatings and the substrate was improved when the substrate was already treated by anodic oxidation or H2O2 was used during the electrodeposition.
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