Preparation Of Medical Degradable Magnesium Alloy And Study Of Bone Screw Size Optimization And In Vitro Performance

As a human implant material,magnesium alloy has great development potential,especially for fixation after bone injury.Bone screws are representative devices used for internal fixation.However,after being implanted in the human body,magnesium alloy bone screws bear complex loads in all directions,resulting in stress concentration and rapid local degradation,and cannot provide sufficient mechanical strength for load-bearing Location.Therefore,this study optimized the size of the metal bone screw HAQPA03,and verified the reliability of the optimization through experiments to improve the stress concentration of the bone screw when implanted in the human body,and improve its load-bearing capacity and corrosion resistance.In this study,Mg-3Zn-0.2Ca-0.7Mn(ZXM)alloy materials and Mg-3Zn-0.2Ca-0.3MgO(ZX)composite materials were prepared.First,the microstructure,mechanical properties and corrosion resistance of the material were characterized;secondly,a three-dimensional model of the bone screw was established,and the mechanical properties were analyzed by the simulation analysis software ANSYS Workbench 19.2,including the three-point bending experiment,Torsion experiment,pull-out experiment,the simulation results of the stress concentration of the screw under different loads are obtained,and then the dimensional parameters such as the inner diameter,pitch,and tooth angle of the screw are changed,respectively,models of different parameters are established,and the three types of parameters are explored.Simulate the influence law of the experiment,and analyze the multi-factor coupling effect through the orthogonal experiment;finally,the screw before and after the optimization is processed,and the mechanical performance experiment(three-point bending experiment,torsion experiment,pullout experiment)and in vitro Soaking(SBF)experiment.The main conclusions are as follows:(1)After solution extrusion,the grain size of ZXM material and ZX material are2.3?m and 3.9?m,respectively.At room temperature,the ultimate tensile strength of ZXM material is 316 MPa,and the ultimate tensile strength of ZX material is 270 MPa.The polarization potentials of ZXM and ZX in SBF are-1.54 V and-1.72 V,ZXM alloy shows better corrosion resistance.(2)The finite element analysis of the bone screw shows that the stress concentration area of the bone screw is mainly the thread part,and the inner diameter is also an important parameter that affects its mechanical properties.The optimized bone screw parameters are: inner diameter 2.5mm,pitch 1.15 mm,tooth profile angle? is 7°,and tooth profile angle ? is 40°.(3)It is found that the optimized mechanical properties of the bone screws are significantly improved.In vitro immersion experiments show that the optimized bone screws have stronger corrosion resistance and more uniform corrosion than before optimization.The total mass loss of screws before optimization of ZXM material is26.7% after immersion,the total mass loss after optimization is 14.8%,and the total mass loss is reduced by 11.9%.The total mass loss of screws before optimization of ZX material is 35.9% after immersion,the total mass loss after optimization is 14.6%,and the total mass loss is reduced by 21.3%.