Corrosion Behaviour And Biological Activity Of Micro-arc Oxidation Coating Coupled With Puerarin On Magnesium Surface

Magnesium and magnesium alloys have high potential as implant materials due to their good biocompatibility and degradability.They can also solve the problems of stress shielding,secondary surgical removal of traditional titanium alloys and other implants.However,the degradation rate of magnesium in vivo environment is too fast,resulting in a large amount of hydrogen production and alkalization of the body fluid environment around the implant,thus inhibiting wound healing and leading to tissue necrosis.Therefore,it is urgent to improve the corrosion resistance of magnesium and its alloys.Composite functional coatings with corrosion resistance and bioactivity were prepared on pure magnesium surface to reduce the degradation rate in vivo and promote bone growth at the same time.Porous ceramic coatings were prepared on pure magnesium surface by ultrasonic micro-arc oxidation(UMAO).Puerarin,a traditional Chinese medicine extract with different concentrations,was coupled with phytic acid(PA),silane(SCA)and silane/phytic acid(SP)to form a biologic composite coating.The structure,element distribution and functional groups of the coatings were analyzed by scanning electron microscopy,energy dispersive spectrometry,infrared spectroscopy,X-ray photoelectron spectroscopy and liquid chromatography.The wettability and corrosion resistance of the coatings were analyzed by wetting angle instrument and electrochemical workstation,and the coatings with better corrosion resistance were selected to study the biological activity in vivo through animal implantation.The experimental results showed that the porous surface of pure magnesium after UMAO electrical breakdown had defects of through pores,which makes body fluid penetrate into the magnesium matrix and causes corrosion.PA drug-loaded composite coating,SCA drug-loaded composite coating and SP drug-loaded composite coating could achieve sealing,and made up for the defects of UMAO coating.The presence of C-C,C-O and C=O functional groups indicated that puerarin was loaded into the coating.The initial release concentrations of PA,SCA and SP-conjugated puerarin were 28.6?g/mL,4.91?g/mL and 25.4?g/mL,respectively.The drug loading was PA coating>SP coating>SCA coating.The Si-O-Si dense skeleton structure of silane provided less space than the large chelating ring formed by phosphate in phytic acid,and the filling amount of Puerarin was smaller.The corrosion resistance of the coating was SCA coating>SP coating>PA coating.The corrosion resistance of these coatings was high than UMAO coating.The self-corrosive current density of SCA-3mg/mL coating reached the minimum of 0.08?A/cm~2 and the maximum impedance.Three coatings were implanted in vivo and found to promote the formation of new bone,which was superior to the UMAO group.The composite coatings on the surface of UMAO were obtained by different coupling agents loaded puerarin.The drug-loading layer first degraded,and the inner layer of UMAO did not degrade until the 8th week.The release of puerarin from the drug-loaded coating at the early stage of degradation promoted bone growth,reached the dynamic balance between bone growth and degradation of magnesium coating,and improved the activity of the coating.After silane/phytic acid double-coupling puerarin,the drug release concentration was25.4?g/mL,the corrosion resistance and biological activity were excellent,and the comprehensive performance was the best.