Preparation And Biocompatibility Of Mg-4.0 Zn-0.8 Sr Alloy With Multilayer Self-Assembled Biomedical Coating

With the development and progress of science and technology,many new materials have been put into the medical field.Magnesium and magnesium alloys attract more and more researchers' attention because of their excellent biocompatibility.However,the rapid degradation rate of magnesium alloy in vivo severely limits its application.In view of this,researchers have taken the means of surface modification to improve the biocompatibility and corrosion resistance of magnesium alloy,and comprehensively improve the performance of magnesium alloy,making the application of magnesium alloy in the medical field possible.In this experiment,according to the requirements of orthopaedic materials and referring to the previous experimental results,the mechanical properties,degradability and biocompatibility of the materials were considered.The Mg-4.0Zn-0.8Sr alloy was prepared,and the composite coatings of anodic oxide film,silane conversion film and chitosan film were prepared on its surface.The corrosion resistance and biocompatibility of the corresponding samples were studied Compatibility evaluation.The results are as follows:(1)after heat treatment,the grain size of Mg-4.0Zn-0.8Sr alloy is slightly larger than that before heat treatment,and the second phase is obviously changed and dispersed in the matrix of Mg alloy,which improves the properties of Mg alloy.The elastic modulus of the alloy is 4.2 GPA,the yield strength is 81.5 MPa,and the tensile strength is 181 MPa.The mechanical properties of the alloy are similar to those of human bone,which meet the needs of biomedical materials.(2)the best technological parameters for the preparation of anodic oxide film were determined by experiments,i.e.the voltage was 95 V,the time was 20 min,the concentration of NaOH was 60 g/L,the concentration of Na2SiO3 was 60 g/L,the concentration of Na2BaO7 was 80 g/L,the best adding amount of citric acid in the electrolyte was 5 g/dl,the best temperature of electrolyte was 20?,and the self-corrosion current density was 1.6 ?A/cm2.The optimal parameters for the preparation of the silane conversion film are 10 ml/dl KH570 concentration and 35.21 ?A/cm2 self-corrosion current density.The optimum parameters were confirmed by orthogonal experiment:chitosan concentration 2 g/dl,acetic acid 0.2 ml/dl,5 layers,glycerin 1ml/dl,self corrosion current density 18.38 ?A/cm2.The anodic oxide film was sealed with sodium silicate.The results of electrochemical impedance spectroscopy showed that the fit resistance porous layer was 7692?,and the dense layer was 3327 ?.(3)the weight loss rate of Mg-4.0Zn-0.8Sr alloy with or without coating is 0.708 g/(m2·h),which is much higher than that of uncoated Mg-4.0Zn-0.8Sr alloy 2.069 g/(m2·h).The results of pH value and the macromorphology of the samples were in accordance with the change of weight loss rate.The coating can protect the magnesium alloy matrix,improve its corrosion resistance and slow down its degradation rate.Through the electrochemical impedance spectroscopy test,the change of magnesium alloy coating is well reflected.The failure time of multi medium coating is much longer than that of single coating.The coating effectively improves the corrosion resistance of magnesium alloy samples.(4)through the hemolysis rate test and platelet adhesion test,it was confirmed that all samples had good biocompatibility.The hemolysis rate of the magnesium alloy samples without coating reached 3%at the highest after being immersed in normal saline for 7 days,and the hemolysis rate of the samples prepared with coating was greatly reduced,meeting the requirement of less than 5%.The morphology of platelet adhesion showed that there was no platelet degeneration and further aggregation in each group,good biocompatibility.The results of animal experiments showed that the health of rats was the most affected by the uncoated magnesium alloy samples within 15-30 days after implantation into the femur of rats.The concentration of magnesium ion in the blood reached 2 mmol/L.at the same time,there was obvious inflammatory reaction in the bone of the implanted area,and the kidney also had a great influence.The glomerulus was swollen,some glomeruli were disappeared,and the magnesium alloy+anodized membrane+sealed pore+silane membrane+chitosan membrane samples were implanted After 30 days,the concentration of magnesium ion in blood was only 1.31 mmol/L,which had little effect on the tissues and organs of rats,slight inflammation,normal kidney morphology and excellent biocompatibility.There was no effect on the heart,liver and lung of rat.