Preparation And Properties Of Porous Magnesium Alloy For Bone Defect Repair

Inspired by tissue engineering technology,porous scaffolds with osteogenic differentiation ability and biodegradability become ideal bone substitutes in clinic.In recent years,magnesium and its alloy porous scaffolds have been considered as a new generation of biomedical metal materials for repairing bone defects,but their low mechanical properties and high corrosion rate in biological environment limit their clinical applications.Therefore,it is significant to further improve the mechanical properties and corrosion resistance of porous magnesium metal scaffolds by alloying,pore structure regulation and surface modification.In this study,the porous Mg-Zn-Ca-Mn alloy scaffold was prepared by the porous casting method by adding biosafety alloy elements（Zn,Ca and Mn）,and the influence of microstructure on mechanical properties and degradation behavior was explored.After the optimal composition was obtained,porous magnesium alloys with different pore structures were obtained by adjusting the parameters of the porous casting process.NaMgF3 coating was prepared on its surface to explore the influence of pore structure and surface treatment on mechanical properties,degradation behavior and biology of porous magnesium alloy.Based on the above research content,the research results of this subject are as follows:（1）The porous magnesium and its alloys prepared by the percolation casting method have a porosity range of 50-60%,and the average main pore size and connected pore size are 396.81μm and 38.68μm,respectively,using NaCl particles with a cubic structure ranging from 355 to 450μm as the seepage template.The addition of alloy-elements makes the porous magnesium alloy grains finer obviously,and the compression strength and corrosion resistance improve obviously.The porous Mg-1Zn-1Ca-0.5Mn alloy scaffold has the smallest grain size,and the yield strength and elastic modulus are 36.36 MPa and 1.50 GPa,respectively.After soaking in Hank’s solution for 5 days,the corrosion rate was only 1.02 mm/year.（2）By increasing the pore size of NaCl pore-forming agent and template prepressure parameters,the porosity of porous Mg-1Zn-1Ca-0.5Mn alloy was increased from 54.69%to 74.34%,and the average main pore size and connected pore size were increased to 526.84μm and 103.76μm,respectively.The yield strength and elastic modulus decreased to 17.68 MPa and 1.10 GPa respectively,but still met the requirements of mechanical properties of bone tissue engineering scaffold.The corrosion rate of porous Mg-1Zn-1Ca-0.5Mn alloy with porosity of 74.34%decreased to 0.94 mm/year.（3）The coating effect of NaMgF₃coating is good and the matrix is closely bonded with the thickness of about 7μm.After soaking in Hank’s solution for 15 days,the corrosion rate of porous Mg-1Zn-1Ca-0.5Mn alloy with porosity of 74.34%is reduced to 0.07 mm/year,which has met the requirements of clinical implantation.The porous magnesium alloy showed excellent cell activity,biocompatibility and osteogenic differentiation ability after surface treatment.To sum up,this study focuses on the improvement of mechanical properties and corrosion resistance of porous magnesium metal scaffold materials,and successfully prepared porous Mg-1Zn-1Ca-0.5Mn alloy with high porosity and connectivity,suitable mechanical properties and stable degradation rate.The preparation of NaMgF₃coating is expected to repair large segment bone defects.