Preparation And In Vitro Degradation Behavior Of Biomedical Mg-Zn-Ca-xMgO Composites And Its Coating

Biomedical magnesium alloys have became ideal materials for degradable implants because of its similar density and elastic modulus to human bone.However,the high degradation rates of magnesium alloys leads to premature failure of implants,which limits its clinical applications.In order to improve the in vivo corrosion resistance of magnesium alloys,alloying elements and surface treatment are usually used.Based on the research results of our group,nano MgO particles were added into Mg-3Zn-0.2Ca alloy by high shear melt agitation technology and prepared good corrosion resistance and biocompatibility calcium phosphorus coating(DCPD)on magnesium matrix composite.The effects of the addition of nano MgO particles and the preparation of the coating on the mechanical properties,corrosion resistance and degradation behavior of Mg-3Zn-0.2Ca alloy were studied by microstructure analysis,mechanical properties test,surface relative potential distribution,electrochemical test in simulated body fluid,hydrogen evolution test and in vitro immersion test.The results are as follows:(1)After solution treatment,the polarization potential of Mg-3Zn-0.2Ca alloy was increased,the yield strength and tensile strength were significantly reduced,and the hydrogen evolution test showed that there was no significant difference in the degradation rate before and after solution treatment.(2)Nano MgO particles of 0.2 wt%,0.3 wt% and 0.4 wt% were added to Mg-3Zn-0.2Ca alloy to obtain the composite.The results showed that the Mg-3Zn-0.2Ca-0.4MgO(wt%)composite after solution treatment had the best mechanical properties,its yield strength reached 287 MPa,tensile strength reaches316 MPa,elongation was 18.96 %,which was 42.79 % higher than the Mg-3Zn-0.2Ca alloy which had the yield strength of 201 MPa.Hydrogen evolution tests showed that the annual corrosion rate of Mg-3Zn-0.2Ca-0.3MgO(wt%)composite was the lowest at 15 days,which was 0.77±0.01 mm/y,52.47 % lower than that of Mg-3Zn-0.2Ca alloy(1.62±0.11 mm/y),indicating that the addition of Nano-MgO particles significantly improved the corrosion resistance of Mg-3Zn-0.2Ca alloy.(3)The annual corrosion rate of Mg-3Zn-0.2Ca-0.3MgO(wt%)composite modified by DCPD coating was 0.41±0.01 mm/y,which was 46.75 % lower than that of matrix Mg-3Zn-0.2Ca alloy(0.77±0.01 mm/y),further improving the corrosionresistance of matrix.It is confirmed by biological tests that the coating magnesium alloy was not toxic and teratogenic,and has good biocompatibility.