| As biodegradable medical metal materials with excellent mechanical properties,biodegradable properties and biocompatibility,Mg alloys have become a hot topic in the research of materials and medicine in recent years.Due to the rapid rate of degradation of Mg alloys,the surface modification method for reducing the corrosion rate of magnesium alloys have been used in order to meet the requirement of clinical applications.Phosphating treatment is a simple and effective method for improving the corrosion resistance of Mg alloys.This work use anhydrous organic solvent ethylene glycol to prepare phosphating solution creatively,to prepare phosphate coating in biomedical Mg-Sn-Mn alloy with good corrosion resistant properties and carry out research on its technology and performance.In this paper,ethylene glycol was used as the solvent of phosphating solution,phosphoric acid?H3PO4?and manganese nitrate?Mn?NO3?2?was selected as the film-forming agent,the influence of different ingredients and concentration,and different treatment process parameters to the effect of Mg-Sn-Mn alloy surface phosphate coating were studied.Scanning electron microscopy?SEM?and electrochemical polarization curves were used to characterize phosphate coating,and the results showed that the optimal concentration of phosphating solution film-forming agent was 0.10mol/L,the concentration ratio was 1:1;optimal phosphating process parameters were:phosphating time 30min,phosphating temperature60?.The SEM resault showed that the surface morphology of Mg-Sn-Mn alloy phosphate coating was flat and uniform,and tiny cracks and granular second phase Mg2Sn existed in the film.Section morphology showed the phosphate coating has dense structure,combined well with matrix,and its thickness was less than 10?m.EDS spectrum analysis and XPS full spectrum scan showed that the main elements of phosphate coating was Mg,Sn,O,P and Mn.It concluded that the film is mainly composed of Mg3?PO4?2 and Mn3?PO4?2 two compounds components by the fitting analysis result of high-resolution scanned XPS spectra.After analyzing the phosphate coating formation mechanism,it accounted that Mg-Sn-Mn alloy film-forming reaction in the phosphate solution consists of two parts,H+consumption and phosphate production.Since the dissolution reaction of magnesium and reaction of H+and NO3-,consumed a lot of H+,leading to the reaction to generate Mg3?PO4?2 and Mn3?PO4?2moved to the right,thereby producing phosphate precipitates.The phosphates nucleated,crystallized and grew on Mg-Sn-Mn alloy surface,forming phosphate coating.Electrochemical test method and immersion experiment were used to characterize the corrosion resistance of the Mg-Sn-Mn alloys both before and after phosphate treatment in simulated body fluid?SBF?.The polarization curves results showed that the corrosion potential of the phosphate treatment Mg-Sn-Mn alloy elevated from-1.674V to-1.414V,the corrosion current density decreased from 126?A/cm2 to 2.42?A/cm2,the theoretical corrosion rate was only 1.7%of the untreated magnesium alloy.The immersion experiment results showed that,the pH value of phosphated Mg-Sn-Mn alloy soaking solution was always lower than the untreated Mg-Sn-Mn alloy samples.After 20d's immersion,the weightlessness of phosphated Mg alloy was?3.21±0.39?%,far less than?12.2±0.59?%of the untreated Mg alloy.After immersion,both the macroscopic morphology and the SEM microstructure of Mg-Sn-Mn alloy samples showed that,the presence of phosphate coating significantly reduced the Mg-Sn-Mn alloy degradation rates in SBF and improved the corrosion resistance of Mg-Sn-Mn alloy.The in vitro biocompatibility of Mg-Sn-Mn alloy before and after phosphate treatment were analyzed by contact angle measurement,cytotoxicity test and hemolysis rate test.The results showed that the contact angle of the Mg-Sn-Mn alloy after phosphate treatment reduced significantly,the phosphated Mg alloy had better hydrophilicity.Cytotoxicity test results indicated that the cytotoxicity of phosphated Mg-Sn-Mn alloy to MG63 and VSMC was?grade,higher than untreated Mg alloys.The hemolysis rate test results showed that the hemolysis rate of Mg-Sn-Mn alloy before and after phosphate treatment was 7.7%and8.0%,respectively,there was no significant differences between them. |
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