| Ti-6Al-4V alloy is widely used as bone substitute due to its excellent processability,mechanical properties,biocompatibility and low toxicity.However,its properties and structure are quite different from that of bone,leading to the fretting in the interface.Besides,friction corrosion easily occurs in humoral environment and produces metal debris,which resulting in metal debris leading to inflammation.In addition,the young's modulus of Ti-6Al-4V alloy is much higher than that of cortical bone,which will produce"stress shielding"and induce osteoporosis.In this study,the bioactive coating for 3D printing porous titanium alloy scaffolds was constructed by micro-arc oxidation to the biological inertia,aimng at the corrosion resistance and high elastic modulus of titanium alloy.At the same time,a calcium phosphorus coating was designed and constructed on the surface of the micro-arc oxidized titanium through the thermodynamic analysis of the deposition of calcium phosphorus phase and mineralization behavior in simulated body fluid.The control of coating microstructure was realized and the deposition mechanism of the coating was clarified.The mineralization behavior and the evolution of electrochemical properties of calcium phosphorus coating in simulated body fluid were studied.The internal relationship between microstructure and biological activity of the coating was established,and the mineralization mechanism of the coating in vitro was proposed.Graphene oxide(GO)additive was introduced into the coating to further improve the biological activity,corrosion resistance and cell metabolic activity of the coating.The effect of GO on the coating formation was also discussed.The formation process,microstructure and thickness of micro-arc oxidized layer were studied.It was found that the layer not only improved the corrosion resistance of titanium alloy,but also improved the biological activity of titanium alloy by increasing the nucleation site of hydroxyapatite(HA).The complex topological structure of 3D printing porous titanium alloy scaffold affected the surface charge distribution,and then affected the morphology and uniformity of the layer.MC3T3-E1 cells grew in the space of the scaffold to form mechanical binding,which is conducive to improve the biological fixation of the implant.The effects of cathodic electrodeposition parameters(deposition current density,temperature and time)on the microstructure of Ca P coating on the surface of micro-arc oxidized titanium were systematically studied.The phase evolution law of calcium phosphorus coating with the increase of deposition temperature and current density was revealed:calcium hydrogen phosphate dihydrate(DCPD),DCPD+HA and HA.The designed dual phase structure of DCPD+HA was formed by adjusting the temperature of the electrolyte and current density.When the deposition temperature remained constant,higher deposition current density and longer deposition time will lead to Ca(OH)2 deposition.The morphology of DCPD,HA and Ca(OH)2 nucleated and grown on micro-arc oxidized matrix was cauliflower-like structure,while the morphology of that nucleated and grown on cauliflower was small particle or needle-like structure.It was found that the composition of the coating was single-phase DCPD at the initial stage of deposition,and HA was deposited on the surface of DCPD after 30 min.The effects of different electrodeposition parameters on the properties of the coatings were studied.It was found that the microstructure of the coatings significantly affected the mineralization and electrochemical behavior of the coatings during immersion in simulated body fluid.Calcium phosphorus coatings could induce HA deposition in simulated body fluid,thus improved the mineralization performance of matrix.Due to the rapid dissolution of single DCPD coating in simulated body fluid,HA deposition was promoted while the protective effect on the substrate was reduced.Although a single HA coating can be stable in simulated body fluid and effectively protect the matrix,its mineralization performance is weak.Only DCPD+HA dual phase coating showed excellent mineralization and electrochemical properties.Three kinds of carbon material additives containing oxide layers were constructed by micro-arc oxidation.The additives had no obvious effect on the oxidation process and the composition of the oxide layer,but improved the corrosion resistance,biological activity and cell adhesion.The micro-arc oxidized layer containing GO had better corrosion resistance,the mineralization property was increased by 11%,and it had the ability to promote the osteogenic differentiation of MC3T3-E1 cells.At the same time,GO/DCPD+HA composite coating was constructed on the surface of micro-arc oxidized titanium alloy.By comparing the microstructure,mineralization properties and formation kinetics of DCPD+HA and GO/DCPD+HA coatings,the influence of GO on the deposition of DCPD+HA coating was revealed.GO promoted the formation of HA by providing more nucleation sites for HA at the initial stage of electrodeposition,and affected the morphology of HA and DCPD phases.With the addition of GO,the mineralization property of the coating was increased by 12%,and the corrosion resistance and cell metabolic activity of the coating were significantly improved. |
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