In Suit Preparation And Biological Properties Of TiO₂-BaTiO₃ Composite Coating On Titanium Alloy

The introduction of BaTiO₃ piezoelectric material into medical titanium alloy substrate can give it bioelectric activity similar to that of natural bone.It has important clinical significance for improving the bioactivity of medical titanium alloy.In this topic,a TiO₂-BaTiO₃ composite coating was in-situ constructed on the surface of titanium alloy by micro-arc oxidation-hydrothermal method.Through studying the effect of different hydrothermal parameters on the morphology,composition and properties of TiO₂-BaTiO₃ composite coating,BaTiO₃ coating was obtained,and the formation mechanism was studied.At the same time,the effect of the post-polarization coating on apatite deposition under static and dynamic loading conditions was compared using a cyclic stress loading device,and the biological toxicity of the coating was evaluated by in vitro cell experiments.The results obtained are as follows:(1)TiO₂-BaTiO₃ composite coating was prepared by micro-arc oxidation-hydrothermal treatment.The concentration of Ba(OH)2 in the hydrothermal solution was 0.3 mol/L,the hydrothermal temperature was 2000 C,and the hydrothermal time was 12 hours.The resulting composite coating surface is smooth and complete.The formation process of BaTiO₃ coating is dominated by the dissolution-precipitation mechanism in the initial stage of the reaction,and it is converted to the in-situ conversion mechanism in the later stage of the reaction.In the hydrothermal environment,the dissolved cerium ions react with hydroxylated TiO₂ on the surface of the film to react with the surface of the film to form BaTi03 crystal nuclei.As the reaction progresses,the crystal nucleus grows and accumulates to form a barium titanate film.The cerium ions then need to pass over the barium titanate film to complete the growth from the surface to the core.After polarization,the piezoelectric constant d33 of the coating reaches a maximum of 0.78 pC/N,which is comparable to the piezoelectric constant of human bone.The adhesion of the coating to the substrate is 44N.(2)Through simulated body fluid immersion experiments,it was found that the polarization-loaded sample(MAOHPL)deposited bone-like apatite more than polarized-unloaded(MAOHP),unpolarized-loaded(MAOHL)and unpolarized sample(MAOH).After soaking for 7 days,the calcium-deficient hexagonal bone-like apatite was deposited on the surface of the three groups of samples:MAOHPL,MAOHP,MAOHL and MAOH.Their contents were 7.48 mg/mL,4.59 mg/mL,1.36 mg/mL and 3.14mg/mL respectively,indicating that the continuous piezoelectric effect under loading conditions can continuously promote the deposition of apatite.(3)It was found through in vitro cell test(MTT)that the TiO₂-BaTiO₃ composite coating was non-toxic by micro-arc oxidation-hydrothermal treatment.After cells were cultured for 1d,4d,and 7d on the surface of the coating,the cells on the surface of the polarized and unpolarized samples gradually spread on the surface of the material,forming a polygonal shape,and the cells in some regions were connected to one another and spread on the coating surface.The number of cells in the polarized group compared to the non-polarized group indicates that the surface electrical effect promotes cell growth.