| With the development of biotechnology,many materials have been developed and applied to the medical industry.In particular,magnesium alloy has attracted people's attention due to excellent properties.Magnesium alloy has great prospects.However,the excessively fast degradation rate of magnesium alloy limits its application.In order to improve the corrosion resistance of magnesium alloy,people have tried various processes for magnesium alloy.At present,surface modification has become the most commonly used method of magnesium alloy treatment.Surface modification can not only enhance the corrosion resistance of magnesium alloy,but also improve its comprehensive properties and greatly expands its application fields.In this experiment,Mg-4.0Zn-1.0Sr alloy was designed by adding alloy elements to pure magnesium.Then,the biomedical coatings were prepared on the surface of Mg-4.0Zn-1.0Sr alloy by heat treatment,anodic oxidation treatment and subsequent sealing treatment.The effects of various process parameters on the morphology and corrosion resistance of the biomedical coatings were investigated,and the degradability and biocompatibility of the prepared magnesium alloy specimens were studied.Firstly,the Mg-4.0Zn-1.0Sr alloy was prepared by vacuum melting furnace and the alloy was heat treated.The metallographic images illustrate that Mg-4.0Zn-1.0Sr alloy is composed of grey alpha-Mg matrix and black second phase.Mechanical properties test results show that the elastic modulus of Mg-4.0Zn-1.0Sr alloy is 42.40 GPa,the yield strength is 85.49 MPa,and the tensile strength is 136.98 MPa,which are consistent with the parameters of human skeleton and conform to the requirements of biomedical materials.Secondly,four factors and five levels orthogonal experiments were used to carry out anodic oxidation of Mg-4.0Zn-1.0Sr alloy.Through SEM and electrochemical tests,the optimum process of anodic oxidation was determined to be 100 V,35 min,80 g/L NaOH,40 g/L Na2SiO3,110 g/L Na2B4O7,and 10 g/L glucose.Then,the self-corrosion current density of the sample reaches 7.623 ?A/cm2 and the self-corrosion potential reaches-1.3574 V.Then the anodic oxidation samples were sealed by subsequent sealing treatment,and three sealing processes were confirmed.One was boiling water sealing for 1 minute;the other was silane treatment.The volume ratio of silane agent GX-612WD and deionized water is 2:1 and the treated samples were kept at 150? for 20 minutes;the third was to add 10%CAU-524P to silane agent GX-612WD and the treated samples were kept at 150? for 20 minutes.The SBF simulated body fluid immersion tests were carried out on Mg-4.0Zn-1.0Sr alloy specimens with or without coating.It is found that surface treatment can improve the corrosion resistance of the specimens in SBF solution through morphology,weight loss rate of the specimens and the variation of pH.Finally,biocompatibility tests were performed on coated and uncoated Mg-4.0Zn-1.0Sr alloy samples,including hemolysis,cytotoxicity testing,and rat implantation experiments(implanted near the back spine and subcutaneous tissue of the head).The results of hemolysis rate test and cytotoxicity test of all samples meet the national standards.The results of sample quality loss show that the corrosion resistance of coated alloy samples is higher than that of uncoated samples,especially the treated with anodic oxidation and silane.Serum biochemical test and pathological analysis of rats implanted with coated/uncoated Mg-4.0Zn-1.0Sr alloys show that the implantations have no effect on the heart,liver,spine and skull of the rats,but have damage to the kidney.The presence ofcoating can reduce the damage.The sample treated with anodic oxidation and silane treatment(GX-612WD+10%CAU-524P)has minimal damage to the kidneys and shows good biocompatibility. |
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