Study On Insoluble Corrosion Products Of Mg Alloys And Composite Surface Modification Of MAO Mg Alloys

Objective:As a degradable metal material,Mg alloys are widely used in bone implant.However,the rapid degradation rate of Mg alloys in the water-containing environment will lead to biosafety problems,and it is difficult to maintain the mechanical integrity of Mg alloys for a long time.In terms of biosafety,there is no systematic study on the insoluble corrosion products.Hence,the first part of this study mainly studied the insoluble corrosion products of Mg alloys in the cell culture environment,and researched the biocompatibility of the insoluble corrosion products.Micro-arc oxidation?MAO?can significantly improve the corrosion resistance of Mg alloys.However,there are many pores in the MAO coating,and the presence of these pores?especially those pores that run through the MAO coating?allows the corrosion solution to directly corrode the Mg matrix.Therefore,the second part of this study mainly studied the surface modification of MAO-Mg alloys by methacrylated gelatin?GelMA?hydrogel and so on to improve the corrosion resistance of MAO-Mg alloys.Methods:In the first part of the study,AZ91 was immersed in two solutions,cell culture medium and phosphate buffer saline?PBS?,and then placed in a CO₂ incubater for 12 days to obtain and collect insoluble corrosion products of Mg alloys.The optical microscope,X-ray diffraction?XRD?and scanning electron microscope?SEM?were used to analyze the composition and morphology of the insoluble corrosion products.Then AZ91 and Pig iliac endothelial cells?PIEC?were cultured directly to study whether insoluble corrosion products could be formed under the co-culture of Mg alloys and cells.Subsequently,the insoluble corrosion products were cultured with PIEC for 1,3 and 5 days to study the biocompatibility of the insoluble corrosion products.In the second part of the study,MAO-Mg alloys were treated with hydrothermal treatment,GelMA hydrogel coating and alginate hydrogel coating.GelMA/hydrothermal/MAO-Mg alloys and GelMA/MAO-Mg alloys with the different numbers of dip-cating?0,1,5,10,15 and 20 times?were prepared.Alginate/hydrothermal/MAO magnesium alloy and alginate/MAO magnesium alloy were also prepared.Scanning probe microscope?SPM?and SEM were used to analyze the morphology and coating thickness,etc,of the Mg alloys,and then the corrosion resistance was tested by electrochemical method.Results:Part I:the results of the immersion experiment showed that the degradation rate of AZ91 in cell culture medium was larger than that in PBS.The results of optical microscope showed that the insoluble corrosion products were formed during the immersion test,and they had various forms:the needle-like shape,the circular aggregates,and the square-radial shape.The results of XRD and SEM showed that the insoluble corrosion product was MgCO₃·3H₂O in the square-rod shape.The results of co-culture of AZ91 and PIEC showed that insoluble corrosion products could form under the co-culture of Mg alloys and cells.The co-culture results of MgCO₃·3H₂O and PIEC showed that MgCO₃·3H₂O had the inhibition effect on the cell growth and proliferation,and its morphology gradually changed from the square-rod shape to the needle-like shape and circular aggregates.Part II:compared with MAO-Mg alloys,the corrosion rate of MAO-Mg alloys treated with GelMA hydrogel decreased;after hydrothermal treatment,the corrosion rate of MAO-Mg alloys reduced.The corrosion rate of MAO-Mg alloys after the co-treatment of hydrothermal and GelMA hydrogel showed no significant change trend.The corrosion rate of MAO-Mg alloys treated with alginate hydrogel decreased,as well as MAO-Mg alloys after the co-treatment of hydrothermal and alginate hydrogel.The corrosion rate of GelMA/hydrothermal/MAO-Mg alloy increased substantially compared to that of GelMA/MAO-Mg alloy.Conclusions:Part I:the corrosion rate of AZ91 in cell culture medium was higher than that in PBS,and the insoluble corrosion product was Mg CO₃·3H₂O.The insoluble corrosion products MgCO₃·3H₂O can inhibit the growth and proliferation of cells.Part II:GelMA hydrogel coating,hydrothermal treatment and alginate hydrogel coating can improve the corrosion resistance of MAO-Mg alloys.