Preparation,Mechanical And Corrosion Properties Of Mg-Zn-Ca-Mn Composites With Biocompatibility

In recent years,magnesium alloys have attracted wide attention as potential implant materials,including Mg-Zn,Mg-Sr,Mg-Ca,and Mg-RE systems.However,the development of degradable and controlled Mg alloys faced some new challenges.Firstly,it was necessary to avoid excessive loss of strength during degradation which would lead to invalidation.Secondly,pitting and surface defects would lead to a rapid decrease in strength.Finally,the degradation rate of most magnesium alloys was faster than the rate of tissue healing,and the release of hydrogen and local alkalization could cause damage to surrounding tissues.Therefore,due to its poor corrosion resistance,conventional magnesium alloys degraded too quickly in the early stage of implantation,and their mechanical properties as a support material were destroyed,which limited their development.Nowadays,people prepared magnesium-based amorphous alloys by rapid solidification,and they found amorphous alloys showed higher strength and lower elastic modulus than pure Mg and conventional magnesium alloys.At the same time,owing to the absence of the second phase in the matrix,the effect of galvanic corrosion was reduced,and improved the corrosion resistance of the material.Therefore,magnesium-based amorphous alloys showed good application prospects in biomedical applications.Based on previous experiments of our research group,it was shown that by introducing 0.5 at.%and 1 at.%of Mn in the Mg₆₉Zn₂₇Ca₄ alloy,the corrosion resistance of the alloy was significantly improved and the elongation ws correspondingly improved.However,the addition of Mn had a large span,so in this study,0.3 at.%,0.5 at.%,0.8at.%,and 1.2 at.%of Mn were introduced into the Mg₆₆Zn₃₀Ca₄ alloy.MgZnCaMn-based crystalline/amorphous composites were prepared by regulation elemental and cooling rates.Experiments showed that the lowest i_coor was 1.43×10^-55 by introduction of 0.8at.%Mn element.By studying the effect of the cooling rate on the microstructure and properties of the alloy,it was found that the compressive strain of Mg_65.2Zn₃₀Ca₄Mn_0.8alloy was 2.32%with a diameter of 2mm,which showed good corrosion resistance and mechanical properties.Subsequently,Sr and Sn microalloying elements with biocompatibility were introduced to the Mg_65.2Zn₃₀Ca₄Mn_0.8 alloy to study the effects on the mechanical and corrosion resistance of the alloy.We found that with a proper amount of Sr addition increased the strength and corrosion resistance of the alloy.The main reason was that a proper amount of Sr made the alloy composition closer to the eutectic point component and improved the alloy's amorphous form ability?GFA?.As a result,the content of amorphous phase in the alloy structure increased,thereby increasing the corrosion resistance and strength of the alloy.The addition of Sn resulted in a finely dispersed crystalline phase in the alloy structure.Therefore,the corrosion resistance was slightly reduced.However,the Sn-bearing alloys showed better corrosion resistance than pure magnesium.With 0.5 at.%Sn addition,the self-corrosion current density of the alloy was on the same order of magnitude as that of Mg_65.2Zn₃₀Ca₄Mn_0.8 alloy,and Sn0.5 alloy composed good mechanical properties.Finally,the effects of Sr and Sn on the biocompatibility of Mg_65.2Zn₃₀Ca₄Mn_0.8 alloy were studied.Cytotoxicity experiments showed that 30%of the Sr0.5 and Sn0.5 alloy extracts were co-cultured with rat preosteoblasts for 3 days.The relative cell proliferation rates were 1.16 and 1.06,respectively.That indicated that Sr0.5 and Sn0.5 showed good cell compatibility,cell toxicity was on the grade 0.In vitro antibacterial experiments demonstrated that the antibacterial rate of the alloy extract on the first day of bacterial co-culture after one day of leaching was 70%.After the bacteria and the extract were continued to be cultured for 3 days,the antibacterial activity for one day of leaching was about 94%,and the antibacterial effect after 3 days of leaching reached about 98%.Both aggregates showed good cell compatibility and antibacterial properties.