Preparation And Characterizationof Hydroxyapatite/Graphene Oxide Composite Coating On Magnesium Alloy

Magnesium(Mg)and Mg alloy are the most promising orthopedic implants due to its non-toxicity,biodegradability,elastic modulus similar with human bone tissue and could avoid stress-shielding effect.However,Mg and Mg alloy have poor corrosion resistance in physiological body environment,the implants will lose its mechanical integrity before the damaged bone heal and finally results in surgical failure,thus limit the application of Mg alloys in clinic.Therefore,how to enhance the corrosion resistance of Mg alloys have become a hot research topic in recent 10 years.In this paper,in order to improve the corrosion resistance and biocompatible of Mg alloys,micro-arc oxidation(MAO)method and biomimetic mineralization method were used to prepare micro-arc oxidation/hydroxyapatite/graphene oxide composite coating(MHAGO)and micro-arc oxidation/hydroxyapatite/graphene oxide/mineralization coating(MHAGO-24)respectively.The surface morphology,phase composition,chemical composition of the coatings were studied by XRD,SEM,TEM,EDS,FTIR and XPS.The corrosion resistance of the surface modified Mg alloy samples were studied by potentiodynamic polarization and electrochemical impedance spectroscopy in simulated body fluid(SBF).The in vitro degradation was also examined in SBF.The SEM and XRD result of MHAGO coating showed that the coating is consist of HA,GO,Mg3(PO4)2,MgO and Ca3(PO4)2 and the thickness of the coating is about 11 μm,the coating surface became rough but the coating porosity was reduced because of the introduction of hydroxyapatite/graphene oxide(HA/GO)composite powder.Potentiodynamic polarization studies in SBF show that the corrosion potential of Mg alloy substrate and micro-arc oxidation coated Mg alloy were-1708 mV and-1598 mV respectively,the corrosion potential of Mg alloy with MHAGO coating was increased to-1472 mV.Because the introduction of HA/GO composite powder reduced the generation of pores and cracks.The micro-arc oxidation/hydroxyapatite/graphene oxide/mineralization(MHAGO-24)coating was prepared by biomimetic mineralization method base on the MHAGO coating.The SEM and EDS results show that the MHAGO-24 sample was covered completely by mineralization layer after 24 h mineralization.The XRD results indicate that the flaky or banding calcium phosphate is hydroxyapatite.The potentiodynamic polarization research show that the corrosion potential of MHAGO-48 coated sample is-1395 mV and the corrosion current density is 1.72 μA·cm-2 which indicate that the MHAGO-48 coated sample have better corrosion resistance than MHAGO coated sample.The result of vitro SBF immersion test demonstrated that the MHAGO-48 coating could effectively control the degradation rate of Mg alloy substrate.