Corrosion Resistance And Biocompatibility Of Biodegradable Magnesium Alloy By Coating Graphite Carbon Nitride（g-C₃N₄）

Magnesium has good mechanical properties,biodegradability and biocompatibility.Its good mechanical properties include similar fracture toughness,elastic modulus and comparative strength to natural bone so that magnesium is regarded as an optimal biodegradable metal implant material.However,magnesium can be corroded easily in vivo,especially in an environment containing chloride,which results in local pH increase,premature mechanical failure and other adverse reactions.In this study,one-step chemical vapor deposition method using urea as a precursor was used to deposit carbon nitride film on the magnesium alloy to allow it to achieve a good corrosion resistance and biocompatibility.The material composition and characteristic functional groups of the as-prepared films were characterized by using X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FTIR）,energy dispersive spectroscopy（EDS）and X-ray photoelectron spectroscopy（XPS）.The surface morphology of the carbon nitride film on the magnesium alloy was observed by using a scanning electron microscope（SEM）and an atomic force microscope（AFM）.The corrosion resistance of magnesium alloy was investigated via the electrochemical method and immersion test.The biocompatibility and hemolysis rate of graphitic carbon nitride films were studied via the hemolysis test and cell experiments.The results showed that carbon nitride film was successfully prepared.The as-prepared film was smooth and dense,and its surface roughness was 2.08 nm.The results from the potential dynamic polarization test showed that the coating significantly reduced the self-corrosion current(i_corr).The results from the immersion test in simulation human fluid（PBS）showed that the coating decreased the hydrogen release significantly and that the p H value kept a lower level compared with the blank magnesium alloy.After coating,the magnesium alloy corrosion resistance was significantly improved.The hemolysis rate of the samples processed at 450℃was 3.6±0.2%,lower than the ISO10993-4 standard value of 5%,which meant that the graphitic carbon nitride film coated magnesium alloy had good blood compatibility.The results of the cell experiments showed the graphitic carbon nitride film coated magnesium alloy had good biocompatibility.The results of the animal experiments showed that the graphitic carbon nitride film coated magnesium alloy had good intergration with host bone tissue.