| The use of biodegradable materials for the internal fixation of fractures is the new development trend of medical materials nowadays.Magnesium and its alloys have a highly promising potential in the field of hard tissue implant materials because of their biodegradability and excellent mechanical compatibility.However,the poor resistance to corrosion has hindered their wider use in biomedical applications.Consequently,magnesium alloys must be modified to ensure their biological safety and compatibility during the service.Micro-arc oxidation(MAO)is a simple and efficient surface treatment technology for magnesium alloys.However,some disadvantages exist in current MAO coatings,including high porosity and less thickness.Traditional methods for improving MAO coatings mainly include adjusting MAO operating parameters,altering the concentration and composition of electrolytes and sealing holes through the post-treatment.Actually,the microstructure of matrix is extremely important for improving the quality of MAO coatings.Therefore,we took sliding friction treatment(SFT)as the pretreatment process for pure magnesium and AZ31 alloy,prior to the MAO treatment,in order to change the microstructure of matrix.The high-quality FG-MAO and NC-MAO coatings were fabricated by combining SFT with MAO technology,which could provide a new approach for designing biodegradable magnesium-based orthopaedic implants.The effects of SFT pretreatment on the structure,composition,corrosion resistance and biocompatibility of the matrix and MAO coating were studied in this paper.The main research contents and results are as follows:(1)The 800 ?m thick deformation layers were successfully fabricated on the surfaces of pure magnesium and AZ31 alloy by the SFT pretreatment technology.The grains existing in the topmost layers of pure magnesium and AZ31 alloy were reduced to fine grain(FG)and nanocrystalline(NC)level,respectively.The corrosion test results showed that the corrosion resistance of the SFTed pure magnesium and AZ31 alloy were improved significantly,which indicated that SFT technology could be used as an effective means to enhance the corrosion resistance of magnesium-based materials.(2)MAO coatings were prepared on the surfaces of the original coarse grain(CG)and the SFTed pure magnesium and AZ31 alloy.Finally,the high-quality FG-MAO and NC-MAO coatings were successfully prepared by combining SFT with MAO technology.It was found that both FG and NC layers successfully survived after MAO processing.The chemical compositions of FG-MAO and NC-MAO coatings exhibited no significant difference from that of CG-MAO coatings prepared on original CG matrices.However,the surface roughness,contact angle and porosity of FG-MAO and NC-MAO coatings were relatively lower,and the coating thickness and the bonding intensity between the coating and matrix increased remarkably.(3)The electrochemical tests and immersion experiments showed that the corrosion resistance of FG-MAO and NC-MAO samples has been significantly enhanced compared with the traditional CG-MAO samples,indicating that the SFT pretreatment is beneficial for improving the quality of MAO coatings.(4)The biocompatibility of CG-MAO and NC-MAO samples was studied by cell proliferation,the hemolysis and platelet adhesion tests.The results of direct test showed that the cells adhered to the surface of NC-MAO coating exhibited multi-antenna morphology,while the adherent cells on the surface of CG-MAO coating showed unhealthy circular feature.The results of indirect test indicated that NC-MAO coating could better promote the adhesion and proliferation of osteoblasts than CG-MAO coating.The results of hemolysis and platelet adhesion test demonstrated that NC-MAO coating had favorable blood compatibility.The improvement of biocompatibility of NC-MAO coating benefited from its high-quality coating structure and excellent corrosion resistance. |
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