| As a new generation of biomedical implant materials,magnesium alloy has attracted extensive attention all over the world because of its good mechanical properties and degradability.However,the chemical properties of magnesium alloys are very active,the degradation rate in human body is too fast,and the biocompatibility is not good enough.These problems limit the clinical application of magnesium alloy as medical implant materials.Therefore,the modification and surface modification of magnesium alloy itself is a hot research at present.Zinc is one of the necessary metal elements for human body.The addition of moderate zinc can improve the corrosion resistance of magnesium alloy to a certain extent;Hydroxyapatite is a bioactive material,which can improve the biocompatibility of magnesium alloys.In this paper,Mg-Zn alloy rod samples with different zinc content were prepared by gravity casting.A bioactive hydroxyapatite coating was prepared on the magnesium alloy substrate by electrophoretic deposition,and then PPy / PCL polymer composite coating was prepared on the surface of nHA coating by chemical polymerization and electrospinning.Finally,nHA/PPy/PCL composite coating was successfully prepared on the magnesium alloy substrate to enhance the corrosion resistance and biocompatibility of magnesium alloy.The outermost PCL spinning coating is doped with an appropriate amount of nano zinc oxide to make the coating have certain antibacterial properties.In the process of preparing Mg-Zn alloy with different zinc content and composite coating,the corrosion product components of the alloy and coating were obtained by X-ray diffraction(XRD),and the microstructure and corrosion morphology of the composite coating were obtained by field emission environmental scanning electron microscope(SEM).The corrosion resistance and biocompatibility of the composite coating samples were analyzed by electrochemical test,simulated body fluid immersion test,cytotoxicity test and antibacterial test.The experimental results show that among Mg-Zn alloys with different zinc content,Mg-6Zn alloy has the best corrosion resistance.After nHA/PPy/PCL composite coating was prepared on its surface,the corrosion resistance and biocompatibility of the alloy samples were significantly enhanced.When nHA coating was prepared on magnesium alloy substrate,the thickness and surface properties of the coating improved with the increase of suspension concentration,and reached saturation state when the concentration reached 0.02kg/L;The thickness,uniformity and density of the coating increased with the extension of aging time,and reached the best level in about 7d;In the range of 0-30 V voltage,the coating thickness increases with the increase of voltage.Therefore,in this experiment,the suspension concentration of 0.02 kg L,aging time of 7d and deposition voltage of 30 V were selected as the best process parameters of electrophoretic deposition.On the basis of using nHA to improve the biocompatibility of magnesium alloy,the outer layer was wrapped with PPy/PCL composite coating to improve the corrosion resistance of the whole sample.The addition of PPy improves the conductivity of the sample surface and lays a foundation for better preparation of PCL coating;The addition of PCL greatly improves the corrosion resistance of the whole sample,and the degradation rate of the sample can be controlled to a certain extent by adjusting the process parameters and experimental time of electrospinning to control the thickness and porosity of PCL coating.In vitro cell co culture experiment showed that the coating could improve the cell proliferation rate to a certain extent.The Mg-6Zn alloy composite with nHA/PPy/PCL composite coating has the highest cell increment rate and the best cell compatibility.The antibacterial experiment results show that the antibacterial effects of nHA,PPy and PCL on Escherichia coli and Staphylococcus aureus are limited,but it is confirmed that the PCL coating prepared by electrospinning can play the role of drug loading by doping drugs in PCL solution,so as to greatly improve the overall antibacterial effect of the composite coating.In conclusion,nHA/PPy/PCL composite coating is coated on biomedical Mg-6Zn alloy to obtain better corrosion resistance,biocompatibility and antibacterial properties,which is expected to become a new type of controllable degradation implant material. |
