Preparation And Characterization Of Hydroxyapatite/Tannic Acid Coating On AZ31 Magnesium Alloys

Magnesium alloys have similar mechanical properties to bone tissues,and can be degraded rapidly under physiological conditions,making them biodegradable materials for orthopedics.However,magnesium alloys also have extremely negative potential and very poor corrosion resistance.In vivo,especially when there is a large amount of chloride ions in the body fluid,the degradation rate is too fast to meet the clinical enough time for bone tissue healing,which will affect bone bonding and limit its application and development in biomedical field.Objective:The hydroxyapatite/tannic coatings on AZ31 magnesium alloys will be prepared to improve the corrosion resistance and biocompatibility of AZ31 magnesium alloys.Methods:tanning acid coating was prepared on the surface of AZ31 magnesium alloy by chemical conversion method.Then hydroxyapatite coating was prepared on the surface of tannic acid coated AZ31 magnesium alloyby biomimetic method.Scanning electron microscopy(SEM),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR)and Energy dispersive X-ray spectroscopy(EDS)were used to perform the relevant characterization of the samples.The corrosion resistance of the samples was studied by potentiodynamic polarization,electrochemical impedance spectroscopy and hydrogen evolution test.The cytocompatibility of the samples was evaluated by MTT method and morphological observation.Results:the characterization results showed that hydroxyapatite/tannic acid coating was successfully prepared on the surface of AZ31 magnesium alloy.Its surface was homogeneous,porous crystal network structure,Ca/P ratio was 1.62,and the coating was well bonded to AZ31magnesium alloys.The corrosion evaluation results showed that the corrosion potential of the HA/TA coated AZ31 magnesium alloy was the highest(1.304±0.006 V vs.AgCl),and its corrosion current density was the lowest((5.649±0.318)×10-~8A/cm2).Compared with AZ31,the corrosion potential of HA/TA/AZ31 increased by about 158mV,and the corrosion current density decreased two orders of magnitude.At the same time,the hydrogen release rate of HA/TA coated AZ31 magnesium alloys was the slowest.The cytotoxicity evaluation showed that the cell proliferation rate of HA/TA coated AZ31 magnesium alloys was higher than 100%.The morphologies of the cultured cells in the extraction of HA/TA coated AZ31 magnesium alloys were similar to negative control group,and the amount of cells of its is the largest.Conclusion:Hydroxyapatite/tannic coatings are successfully prepared on the surface of AZ31 magnesium alloy,and the corrosion resistance and cytocompatibility of the modified AZ31magnesium alloy are greatly improved.Therefore,it lays a certain foundation for the development of biodegradable implant materials.