| Objective:Medical magnesium alloy has a very bright clinical application prospect as a degradable orthopedic biomedical material.However,the biggest obstacle in the application of magnesium alloys for medical materials is that the corrosion rate is too fast,and the corrosion is accompanied by a large amount of gas,which greatly limits the development and application of magnesium alloys.From the perspective of orthopedics,the study of mechanical properties,degradation properties and biocompatibility of magnesium alloys is a research hotspot in the field of orthopedics.Although there are many reports or literatures that have made expectations for biodegradable magnesium alloys as a biocompatible biomaterial for biodegradable orthopedics,degradable magnesium alloys have not yet reached the level of orthopedic clinical applications.The research idea of this thesis is to analyze the selection of alloy composition,through the alloying design and preparation,adding other specific alloying elements in the magnesium matrix to observe the change of its properties,the mechanical properties,corrosion performance and bio-phase of the degradable magnesium alloy.Capacitance,degradation of gas,toxicity and other aspects of research and observation,selection or evaluation of various characteristics and results,to lay the foundation for the future design,preparation and research methods of degradable magnesium alloy,provide a reliable basis support for the development and application of magnesium alloys.Methods:（1）Design and preparation of magnesium alloy material composition,study the role of various alloying elements from medical and metallurgical aspects,analyze and select suitable alloying elements,and prepare biomedical magnesium alloy by casting;The mechanical properties,microstructure and corrosion resistance of magnesium alloys were used to evaluate the performance of magnesium alloys.（2）Magnesium alloy materials In vitro experiments,study the hemocompatibility and cytotoxicity in the biocompatibility of magnesium alloys through studies on hemolytic and cytotoxicity,and as a basis for screening magnesium alloys into the next stage of research.（3）Magnesium alloy materials In vitro experiments,the anti-infective potential and characteristics of magnesium alloy materials were investigated and evaluated by antibacterial experiments.（4）Magnesium alloy materials In vivo experiments,through the observation,blood biochemical examination and imaging examination,the study will observe and analyze the gas production phenomenon of magnesium alloy systematically.（5）Magnesium alloy materials In vivo experiments,through the blood biochemical examination and other methods,research and analysis the toxicity of magnesium alloy to the body on tissues and organs.（6）In vivo experiments of magnesium alloy materials,through pathological examination and scanning electron microscopy experiments,the effects of in vivo magnesium on the surrounding tissues and the formation of fibrous membranes were studied.（7）In vivo experiments of magnesium alloy materials,the degradation mode of in-situ magnesium alloys was studied by scanning electron microscopy.（8）In vivo experiments of magnesium alloy materials,use the methods of gross observation,imaging examination and pathological examination,to study the influence of magnesium alloy on the formation of bone structure.Result:（1）The grain size of the casting alloy is about 50μm,and different amounts of precipitates exist on the grain boundary.The alloys are composed of anα-Mg phase（a solid solution of calcium in magnesium）and a Mg24Y5,CaZn3 phase.Theα-Mg phase is the matrix,the Mg24Y5 and CaZn3 phases are mainly concentrated at the grain boundary,and the difference in the number and morphology of the Mg24Y5 and CaZn3phases leads to the difference in the properties of the alloys.（2）The microhardness test of the alloy found that the microhardness of the magnesium alloy I,the magnesium alloy II,and the magnesium alloy III at dendrite region（dark region）and two-phase region（bright region）increased gradually.Dendritic region（dark area）and two-phase area（bright area）of the magnesium alloy III have the highest microhardness about 108±6.2 MPa and 154.4±5.5 MPa.（3）The tensile mechanical properties of the alloy was tested and it was found that the yield strength and tensile strength of the alloy increased with the increase of zinc content.Magnesium alloy III has the highest yield strength and tensile strength,reaching 85.6 Mpa and 143 Mpa,respectively,and the elongation is 14.9%.（4）The compressive elastic modulus of each group of magnesium alloys is close to 45GPa,and the maximum compressive modulus,compressive strength and compression yield point are 53 GPa,272 MPa and 113 MPa.However,it is still slightly higher than pure magnesium and does not reach the elastic modulus of the bone（<20 GPa）.（5）The standard electrode potential of Mg is-2.375 V.The corrosion potential（-1611mV and-1503mV）and the polarization resistance（0.119/KΩand 0.123/KΩ）of magnesium alloy II and magnesium alloy III in Hank’s solution are higher than that of magnesium.Alloy I（-1654mV and 0.051/KΩ）,and corrosion rates(8.46×10-5/g·cm-2·h-1 and 6.69×10-5/g·cm-2·h-1)are lower than Magnesium alloy I(25.4×10-5/g·cm-2·h-1).（6）When the concentration of magnesium alloy I is 100%,75%,50%and 25%,the hemolysis rate is>5%,the hemolysis reaction occurs,and when the concentration of the extract is≤10%,the hemolysis rate is<5%.No hemolysis reaction;the hemolysis rate of magnesium alloy II and magnesium alloy III group is all<5%.（7）The cytotoxicity of magnesium alloy II and magnesium alloy III was studied by MTT colorimetric method.The results showed that the toxicity grades of magnesium alloy II and magnesium alloy III were both grade 0 and grade 1.（8）Magnesium alloy II and magnesium alloy III can exhibit antibacterial properties against Eco2.The maximum diameter of the inhibition ring is23.25±0.343mm and 23.10±0.415mm,but with selectivity obviously.（9）In terms of gas production,there is no obvious difference between the magnesium alloy groups.The soft tissue embedded magnesium alloy II and magnesium alloy III produce little or no bubbles,and implant magnesium alloy II and magnesium alloy into the femur.There is no air bubbles on the surface of the femur,but gas is produced in the femoral canal.（10）Comprehensive results of blood,biochemical examination and pathology of important organs,magnesium alloy II and magnesium alloy III have no obvious toxic effects on the blood system,heart,liver and kidney,especially the liver.（11）In the inflammatory cell response rate and the fibrous capsule rate,the results of titanium alloy,magnesium alloy II and magnesium alloy III were all grade III at 2w,and were reduced to grade II at 4w.The electron microscopy’s results showed that the average thickness of the fiber membrane of magnesium alloy II was close to twice the thickness of titanium alloy and magnesium alloy III,while the magnesium alloy III and the titanium alloy were substantially flat,about 100μm and larger than 30μm.（12）The healing of the femur is mainly based on the repair of the skeleton.The external skeleton formed from femoral shaft is obvious,and the imaging shows that the formation of the internal skeleton is affected.The contact surface of the implant of titanium alloy,magnesium alloy II and magnesium alloy III have neo-trabecular bone’s formation,the results of BMP-2 immunohistochemical staining show that magnesium alloy II and magnesium alloy III at 2w and 4w compared with titanium alloy,the P value<0.05,and at 8w and 12w,the P value>0.05.Conclusion:（1）Zinc,calcium and strontium are selected as alloying elements.Three magnesium alloys were prepared by melt casting.In the microstructure analysis of magnesium alloy,the grain size of the as-cast alloy is about 50μm,and different amounts of precipitates exist on the grain boundary.The alloys are composed of anα-Mg phase（a solid solution of calcium in magnesium）and a Mg24Y5,CaZn3 phase.（2）The results of microhardness test,tensile mechanical property test and corrosion performance test of magnesium alloy III were better than other magnesium alloys;the results of magnesium alloy compression performance test failed to approach the compression performance of bone.（3）Hemolysis experiments show that the hemolysis rate of magnesium alloy I exists>5%,the hemolysis reaction occurs,and the magnesium alloy I needs to be screened;the hemolysis rate of magnesium alloy II and magnesium alloy III group can reach<5%.Magnesium alloy II and magnesium alloy III were retained.The difference between magnesium alloys should be consistent with the difference of corrosion potential,polarization resistance and corrosion rate.We believe that corrosion potential,polarization resistance and corrosion rate are very valuable for the study of magnesium alloys.The entry point of performance is great significance to the design and manufacture of magnesium alloys and the evaluation of biological properties.（4）The cytotoxicity of magnesium alloy II and magnesium alloy III was studied by MTT colorimetric method.The results showed that magnesium alloy II and magnesium alloy III had no obvious cytotoxicity and met the requirements of biomedical materials.（5）Magnesium alloy II and magnesium alloy III do exhibit bacteriostatic properties and are obviously selective.This selective bacteriostatic property is likely to be related to the addition of strontium.（6）In terms of gas production,there is no obvious difference between the magnesium alloy groups.The soft tissue embedded magnesium alloy II and magnesium alloy III produce little or no bubbles,and implant magnesium alloy II and magnesium alloy into the femur.There is no air bubbles on the surface of the femur,but gas is produced in the femoral canal.（7）Comprehensive results of blood,biochemical examination and pathology of important organs,magnesium alloy II and magnesium alloy III have no obvious toxic effects on the blood system,heart,liver and kidney,especially the liver.（8）In the inflammatory cell reaction rate and the fiber capsule rate,there is no significant difference between alloys.Further scanning electron microscopy results show that the average fiber membrane thickness of magnesium alloy II is close to two times than titanium alloy and magnesium alloy III.While the thickness of magnesium alloy III and titanium alloy is flat basically,but still does not reach the requirement of clinical application.（9）The healing of the femur was mainly based on the repair of the skeleton.The external skeleton formed obviously,and the imaging confirmed that the formation of the internal skeleton was affected.The contact surface of the implant of titanium alloy,magnesium alloy II and magnesium alloy III have neo-trabecular bone’s formation,further BMP-2 immunohistochemical staining results show that magnesium alloy II and magnesium alloy III can increase the expression of BMP-2 in a short period of time,and promote the osteogenesis. |
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