Preparation And Study On Properties Of Medically Degradable Porous Zinc-Magnesium Alloy

As one of the essential trace elements in human body,zinc has the most suitable degradation rate in biodegradable metal materials and is a promising biological material.However,due to the insufficient mechanical properties of pure zinc,the mechanical strength requirements of the implant cannot be met.In order to solve this problem,Mg was used as alloying element to improve the mechanical properties of pure zinc,and the Zn-Mg alloy was fabricated by powder metallurgy method.Moreover,the Zn-Mg alloy with porous structure was prepared by adding space holder.It is hoped that the porous structure of the human cancellous bone can be achieved by preparing a connected pore structure.Firstly,a four-component Zn-xMg?x=0,5,10,15 wt.%?bulk Zn-Mg alloy was designed and prepared.By comparing the density and mechanical properties of the sintered bulk,it is found that the solid solution strengthening of Mg and the precipitation strengthening of MgZn₂ phase are significant,and the comprehensive mechanics of Mg content of 10 wt.%is higher.Therefore,Zn-10Mg is preferred as the matrix for preparing the porous Zn-Mg alloy.In order to achieve the biomimetic effect and be able to match the mechanical properties of cancellous bone,carbamide was used as a pore former in this study.Porous Zn-10Mg alloys with porosity of 10.2%,23.4%,40.4%and57.3%were prepared by designing and controlling the addition of space holder content.The open porosity ranged from 1.4 to 24.7%and the average pore size ranged from 416 to 612?m.The research results are as follows:?1?There is a exponential function relationship between compressive strength,elastic modulus and porosity of porous Zn-10Mg alloy.The pore structure weakens the mechanical properties of the material,with the porosity increasing from 10.2%to 57.3%,the compressive strength of the porous Zn-10Mg alloy decreasing from 99 MPa to 8 MPa,and the flexural strength decreasing from 21.4 MPa to 7.4 MPa.?2?The in vitro degradation behavior of porous Zn-10Mg alloy was investigated by electrochemical test and simulated body fluid?SBF?static immersion test.The results show that the corrosion behavior of porous Zn-10Mg alloys with different porosity prepared by this method is basically the same.As the porosity increases,the corrosion performance is significantly worse.The corrosion process can be divided into three stages:First,the rapid degradation of Mg in the early stage.Secondly,the deposition of corrosion in the medium-term Mg depleted corrosion products rapidly falls,and the dynamic equilibrium corrosion rate increases slowly in the later stage.Thirdly,the stable corrosion rate distribution of the porous sample after static immersion for 28 days was in the range of 0.176-2.516 mm/year.?3?The biocompatibility evaluation of the porous Zn-10Mg alloy showed that the extract had good cytocompatibility with L-929 cells,and the cytotoxicity level was 0-2.The properties of four different porosity Zn-10Mg alloys were compared and the relationship between mechanical strength and porosity was analyzed by Gibson-Ashby model.It was found that the porous Zn-10Mg alloy with porosity distribution in the range of 40.4%-57.3%has mechanical strength and pore structure characteristics closer to human cancellous bone characteristics.And its degradation rate and cytotoxicity are in line with the safe use requirements of biodegradable metal medical materials.The biocompatibility of porous Zn-10Mg can be further verified by in vivo implantation experiments and is expected to be used as a bone filling repair material.