Study On The Degradation Performance And Biocompatibility Of Biomaterials Of Mg-4.0Zn-1.0Sr-0.4Ca With Alkaline And Phosphating Treatment

Magnesium alloys as a new type of medical materials,with the similar mechanical properties of bone,good biocompatibility and degradation in vivo,are gaining increasing attention.But the high degradation rate of magnesium alloys severely limits its application in medicine.So how to control the degradation rate of magnesium alloys becomes the main research direction of medical magnesium alloys.Surface modification is one of the most effective methods for improving the corrosion resistance of samples.In this paper,the cast Mg-4.0Zn-1.0Sr-0.4Ca alloy and Mg-4.0Zn-0.4Ca alloy were prepared for studing the effect of Sr element on the mechanical properties,corrosion properties and microstructure of alloys.The coating on the surface of Mg-4.0Zn-1.0Sr-0.4Ca alloy was prepared by alkali heat and phosphating treatment to compare the degradation corrosion properties of alloys in SBF solution.The coating formed on the magnesium alloys was characterized by XRD and the morphology of sample surfaces were observed by SEM.At last,the biocompatibility of the bare alloy and coated alloy were studied by hemolysis rate measurement and the implantation experiment.Main results were as follows:(1)Mg-4.0Zn-1.0Sr-0.4Ca alloy had better mechanical properties than Mg-4.0Zn-0.4Ca alloy,whose tensile strength were 169.49 Mpa,110.36 MPa;yield strength were 80.12 MPa,63.15 MPa;dimensional hardness were 82.13 HV,70.94 HV;The gold phase diagram showed that the grain distribution of Mg-4.0Zn-1.0Sr-0.4Ca was more uniform and finer than that of Mg-4.0Zn-0.4Ca.These phenomena show that the addition of Sr element refine the grains of the alloy and improve the hardness,tensile strength and yield strength of the alloy.(2)Mg-4.0Zn-1.0Sr-0.4Ca alloy had better corrosion resistance properties than Mg-4.0Zn-0.4Ca alloy,whose electrochemical corrosion potential were-1.3812 V,-1.5066 V;corrosion currents were 1.02×10-5 A·cm-2,2.52×10-5 A·cm-2.These phenomena show that the addition of Sr element improves corrosion potential and reduces the corrosion current.(3)Mg-4.0Zn-1.0Sr-0.4Ca alloy was prepared by alkali heat and phosphating treatment respectively,whose electrochemical corrosion potential were-1.32 V,-1.312 V;corrosion currents were 7.9953×10-6 A cm-2,1.0744×10-6 A·cm-2.These phenomena show that surface modification improves corrosion resistance of alloy.(4)Weight loss of the Mg-4.0Zn-1.0Sr-0.4Ca alloys with or without coating after 2,4,8,11,14,17 days of immersion in SBF show that weight loss of the alloys with coating were obviously lower than that of the bare alloy.The pH change of the corresponding immersion liquid of the alloy with coating was much smaller than that of the bare alloy.These phenomena show that the coating slow degradation rates of alloys.(5)The hemolysis rates of Mg-4.0Zn-1.0Sr-0.4Ca alloy with and without coating are 28.1%,1.79%and 0.3%respectively and the hemolysis rates of the coating alloys were less than 5%.These phenomena show that the coating alloys have fine anti hemolytic properties,(6)The detection results of the various organs of rats within a month implantation show that the rats all have different levels of inflammation.The rats with coating specimens were in inflammatory acute phase.The rat with the bare alloy was in the recovery phase.These phenomena show that the degradation rates of alloys were slowed down by the coating.