| As a light structural material,magnesium alloy has low density,high specific strength and good processability.It has been widely used in automobile,chemical industry,military and electronic fields.At the same time,magnesium is an essential trace element for human body,and has good biodegradability and compatibility.Therefore,magnesium alloy has great development potential in the biomedical field.Compared with traditional titanium alloy and other medical metals,magnesium alloy is harmless to human body after degradation,and can avoid the trouble of second surgery.However,the poor corrosion resistance of magnesium alloy and the rapid degradation rate often lead to the failure before the heald of injured tissue,which greatly limits the clinical application of magnesium alloy.Therefore,how to improve the corrosion resistance of magnesium alloys has become a key issue to break through its limitations and expand its applications.Calcium phosphate（CaP）is highly similar to the main inorganic components of human bone,which has good biocompatibility and osteoinductive effect.It is one of the commonly used coatings on the surface of magnesium alloys implanted in orthopedics.However,the CaP coating has a large number of holes,and the improvement of the corrosion resistance of magnesium alloys is limited,so it needs to be compounded with other materials to further improve the corrosion resistance of matrix.Graphene oxide（GO）is an oxide of graphene,with a large number of oxidation functional groups on the surface.It has excellent physical and chemical properties,impermeability and good biocompatibility,which can prevent the penetration of corrosive fluid.In view of the above characteristics,GO can be used as a biomedical coating material to be compounded with CaP to further improve the corrosion resistance and biocompatibility of magnesium alloy.Therefore,in this paper,using AZ60 magnesium alloy as the matrix,CaP film and GO were composite by different methods to prepare CaP/GO composite coating,and the structure,performance and protective mechanism of the composite coating were systematically explored by SEM,XRD,FT-IR,XPS,electrochemical test,immersion test and in vitro cell experiment.The composite method adopted and the main studies are as follows:（1）The GO was composited with the biomimetic deposited CaP coating by adding it in the biomimetic fluid.The magnesium alloy was firstly pretreated by alkali,and the CaP coating was biomimetic deposited on its surface.At the same time,a certain content of GO was added in the deposition solution to prepare the CaP/GO composite coating.The recombination of GO can accelerate the deposition process and reduce the defects of CaP film.The results show that the corrosion resistance of CaP/GO composite coating is significantly improved,and the corrosion current density is only 2.9×10-7 A/cm~2,which is two orders of magnitude lower than that of magnesium alloy,and the corrosion potential shifts positively.The total amount of hydrogen evolution in immersion experiment decreased obviously,indicating that the corrosion resistance was improved significantly.Meanwhile,the cell experiment results showed that the biocompatibility of CaP/GO composite coating samples was significantly improved,the cell survival rate was significantly improved,and the cell adhesion morphology was great.In addition,the SEM images after immersion for 7 days reflect that the coating has obvious mineralization,indicating that the CaP/GO composite coating has good biological mineralization ability.（2）The GO was composited with the biomimetic deposited CaP coating by spinning it on the surface of coating.A polydopamine（PDA）pretreatment layer was first deposited on the surface of the magnesium alloy,then a CaP coating was biomimetic deposited on it,and finally GO was spin-coated to prepare a PDA/CaP/GO composite coating.As a sealing layer,GO can reduce surface defects of CaP coating and further improve its corrosion resistance and biocompatibility.In addition,two different dispersants,ethanol and water,were used in the spin coating of GO,and the influence of dispersants was studied.The results show that the performance of the composite coating with water as the dispersant has the most significant improvement,and its corrosion current density is 3.2×10-7 A/cm~2,which is two orders of magnitude lower than that of the magnesium matrix.The total amount of hydrogen evolution in the immersion test was only 0.105 m L,and the corrosion resistance was significantly improved.Moreover,the composite coating surface provides more favorable conditions for cell growth.In vitro cell experiments showed that the composite coating promoted cell proliferation and adhesion. |
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