| The development of hard bone tissue is one major focus of tissue engineering. Medical titanium and its alloys are useful products in this field due to their excellent performance. However, the combination of titanium and the bone tissue is just a pure mechanical way within human body, which is rather unstable. Micro-arc oxidation (MAO) is a kind of electrochemical technique that can make the surface of titanium have a kind of porous coating and can improve the bio-activity of titanium. This technique has a bright future in the application of surface processing on titanium and its alloys because it can make a chemical connection between the surface of titanium and the bone tissues.In this paper, by using of Ca(CH3COO)2·H2O-Ca(H2PO4)2·H2O electrolyte, the bio-ceramic coatings with hydroxyapatite(HA) were prepared on pure titanium from two different technical routines: one is MAO and hydrothermal treatment routine and the other is MAO and calcination treatment routine. The surface/cross-sectional morphology, elemental composition, phase composition, thickness, adhesion, corrosion resistance and cyto-compatibility were investigated by using SEM, EDX, XRD, film thickness meter, film adhesion meter, CS300 constant potential rectifier, and cell culture method, respectively. Meanwhile, the comprehensive performance of the coatings formed by the two technical routines was compared, and HA forming mechanism was discussed, as well. The results are as following:Within the Ca(CH3COO)2·H2O-Ca(H2PO4)2·H2O electrolyte system, a kind of coarse and porous coating mainly with titania phase was gained on the surface of pure titanium after the MAO treatment. After hydrothermal treatment, it appeared scale, flaky or needle structures within the coating, which was thicker and denser than before. The ratio of Ca/P of this coating then is 1.68. The autoclave environment on the one hand provides nucleation sites for HA and on the other hand provides a promising environment for HA to nucleate.Within the Ca(CH3COO)2·H2O-Ca(H2PO4)2·H2O-La(NO3)3·6H2O electrolyte system, amorphous phases were gained within the coarse and porous coating after the MAO treatment. And it appeared some heat cracks within such coating. After the calcination treatment, the amorphous phases were tested to be HA and calcium phosphate ceramics. Calcination treatment has made the coating thicker and made the heat cracks deeper and wider. The ratio of Ca/P of this coating then is bigger than that same ratio of natural HA. Although the element of La did not form any new phase within the film, it played an important role in facilitating the formation of HA: it caused unbalanced electron charge, which led the TiO2 water gel to form and later prompted the formation of HA.According to the results of adhesion test, the adhesion of coatings performs better after the hydrothermal treatment; the adhesion of coatings gained from electrolyte with La performs better than that from electrolyte without La, but the calcination treatment makes the adhesion poorer. According to the results of corrosion resistance, all the coatings gained from MAO treatment with or without later treatment have better corrosion resistance performance than pure titanium. After the hydrothermal treatment, the MAO coating performs poorer corrosion resistance; while the calcination treatment, the coating gained from electrolyte with La exhibits better corrosion resistance.Cell-culture is used to compare the cyto-compatibility of four kinds of coatings prepared in this paper as well as pure titanium. The results show that all the coatings have better cyto-compatibility than pure titanium. Hydrothermal treatment can improve the cyto-compatibility performance of coatings, while calcination treatment to some degree lower the cyto-compatibility performance of coatings. |
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