Study On Surface Modification And Regulation Of Electrochemical Corrosion Behavior And Biocompatibility Of Magnesium Alloys

Magnesium alloy has become a research hotspot of degradable metal biomaterials because of its good mechanical property and biodegradability.However,the rapid degradation in physiological environment and poor biocompatibility restrict its applications.Because the corrosion behavior and biocompatibility of the material are closely related to the surface performances,it is of great scientific significance to regulate the electrochemical corrosion degradation behaviors and biocompatibility of medical magnesium alloy by surface modification.In order to improve the corrosion resistance and biocompatibility of AZ31B magnesium alloy,several multi-functional bioactive coatings were constructed on the surface of AZ31B magnesium alloy by in-situ surface modification technologies such as surface chemical treatment,surface self-assembly,surface chemical grafting and layer by layer self-assembly.The electrochemical corrosion degradation behaviors and biocompatibility of the modified magnesium alloy were also studied in detail.?1?The chitosan/heparinized graphene oxide?Chi/HGO?multilayer coating was prepared on the magnesium alloy surface by layer-by-layer self-assembly technology,and the multilayer coating significantly improved the hydrophilicity of the material surface.At the same time,the multilayer coating on the surface significantly increased the corrosion potential of the magnesium alloy and reduced the corrosion current density.In addition,the coating reduced the release of Mg²⁺in the simulated physiological environment and effectively inhibitted the alkaline increase of the surrounding environment.This indicates that the multilayer coating could improve the corrosion resistance of the magnesium alloy.Moreover,the Chi/HGO coating reduced the hemolysis rate,platelet adhesion and promoted the adhesion and proliferation of vascular endothelial cells.?2?The chitosan functionalized graphene oxide/heparin?GOCS/Hep?multilayer coating was successfully prepared on the magnesium alloy surface by in-situ chemical reaction technology and layer-by-layer self-assembly.The coating was not only compact and significantly enhanced the hydrophilicity of the magnesium alloy,and the water contact angle was only 18°for the multilayer coating.The degradation of the magnesium alloy modified by GOCS/Hep multilayer coating was slow,and the relatively complete coating could be maintained after immersion in simulated body fluid for 7 days.On the other hand,heparin released slowly from the coating and it can significantly reduce the hemolysis rate,effectively prevent the platelets adhesion and activation,and thus greatly improve the blood compatibility of the magnesium alloy.In addition,the GOCS/Hep multilayer coating was not only suitable for the adhesion and proliferation of the endothelial cells,but also can promote the vascular endothelial growth factor?VEGF?generation and the nitric oxide?NO?release of the endothelial cells.?3?On the basis of the immobilization of 16-phosphonohexadecanoic acid by self-assembly,GOCS was grafted on the magnesium alloy surface followed by immobilizing heparin and bone morphogenetic protein 2?Hep/BMP2?to prepare GOCS@Hep/BMP2composite coating on the surface.The result of water contact angle showed that the hydrophilicity of the magnesium alloy surface was significantly improved after surface modification.The composite coating can significantly reduce the corrosion tendency and corrosion rate of the magnesium alloy,and the p H values in simulated physiological environment was effectively reduced.These results suggested that the corrosion resistance of the magnesium alloy had been significantly improved.Although the effect of grafting GOCS on the corrosion resistance of magnesium alloy was significant,the blood compatibility was not satisfied.After immobilization Hep/BMP2,the anticoagulant was significantly improved.BMP2 in the surface coating can significantly promote the osteoblast adhesion and proliferation,and up-regulate the expression of alkaline phosphatase?ALP?and osteocalcin?OCN?,indicating that the coating has good osteogenation.?4?The chitosan coating containing zinc and bone morphogenetic protein 2?Chi?Zn/BMP2??was prepared on the magnesium alloy surface by in-situ self-assembly.Hydroxyapatite?HA?was further deposited on the surface to prepare Chi?Zn/BMP2?@HA composite coating.The Chi?Zn/BMP2?coating had a significant effect on improving the corrosion resistance of the magnesium alloy.After the modification,the release of Mg²⁺and the impact on the p H value of the corrosion environment of the magnesium alloy were significantly reduced.However,the blood compatibility of the coating was not satisfactory.The deposition of HA on the surface acquired good hydrophilicity and the water contact angle was only 3.3°.At the same time,it can reduce the platelet activation on the surface and the hemolysis rate.The deposition of HA coating on the surface did not significantly affect the release behaviors of Zn²⁺and BMP2.The Zn²⁺release can reduce the adhesion and proliferation of escherichia coli on the HA surface,and enhance osteoblasts adhesion and proliferation,as well as the ALP and OCN release.?5?After the immobilization of GOCS,zinc?Zn?and propranolol?Pro?were introduced in the coating to prepare GOCS?Zn/Pro?multifunctional coating on the surface.The coating endowed the magnesium alloy with good surface hydrophilicity,and the water contact angle was only 7°.The multi-functional coating can effectively reduce the corrosion tendency,the corrosion rate,and the impact on the p H value of the corrosion environment,and thus effectively improve the corrosion resistance of the magnesium alloy.The coating not only had an obvious effect on platelet adhesion and activation,but also can effectively reduce the hemolysis rate,leading to the improved blood compatibility.Endothelial cells had better growth behavior on the multilayer coating,which endow the magnesium alloy with good cytocompatibility.At the same time,Zn²⁺in the coating had better antibacterial activities,and it can effectively inhibit the adhesion and proliferation of escherichia coli on the surface.In conclusion,in the light of the different applications,this study provides several surface modification strategies that can simultaneously improve the physiological corrosion resistance and biocompatibility of magnesium alloy,and regulate the electrochemical behavior and biocompatibility of medical magnesium alloy.It can be used in the blood contact materials and bone-substituted biomaterials.