Fabrication Of Micro-nanostructures On The Surface Of Micro-arc Oxidation Films On Magnesium Alloys By Femtosecond Laser And Its Influence On Propertie

With the continuous improvement of people living standards,the shortcomings of traditional medical bone implant materials are increasingly apparent.For example,it is not easy to degrade,need a second operation to remove it,and is easy to cause stress shielding.Bacterial infection after clinical device implantation is also a problem.Therefore,it is urgent to develop biomaterials with both degradability and antibacterial properties.Biological magnesium（Mg）alloy can be spontaneously degraded and absorbed by human body.However,magnesium alloy still has defects such as excessive degradation rate and insufficient biocompatibility.In this paper,micro-arc oxidation（MAO）technology was used to prepare Ag-containing antibacterial coating on the AZ31B Mg alloy.The thickness,binding force,surface morphology,phase composition,corrosion resistance,biocompatibility and antibacterial properties of the coating were studied,and the antibacterial mechanism of the coating was discussed.Different micro-nano structures were prepared by changing the femtosecond laser（FSL）parameters to control the degradation rate of Mg alloys.The relevant research results are as follows:（1）The Ag-containing MAO coating was prepared by MAO technology.The morphology,phases,biocompatibility and antibacterial properties of the coating were researched.The results show that there are irregular micropores with different sizes on the surface of the coating.These micropores are interconnected,and smaller micropores can be directly observed from larger pores,but these micropores do not penetrate into the matrix material.The thickness of the coating is about 36μm.The interface between the coating and the substrate is tightly and coherent,and the internal dense layer can effectively prevent the corrosive medium from contacting with the substrate and slow down the corrosion rate.The XRD results show that the addition of CH₃COOAg leads to the formation of Ag₂O phase,and the release of Ag⁺during the degradation process makes the coating exhibit excellent antibacterial properties.The results of electrochemical experiments show that the corrosion current density of the micro-arc oxidation coating is about an order of magnitude lower than that of the magnesium alloy substrate,and the coating shows significant corrosion resistance.Through the analysis of the bonding force,it can be seen that the bonding force between the coating and the substrate is about 9.5N,and the coating prepared by this method has excellent bonding strength.The coating is non-toxic to osteoblasts and has a good proliferation effect,which is conducive to cell growth and has a significant inhibitory effect on E.coli.（2）On the surface of the MAO coating prepared above,groove-like micro-nano structures under different parameters were prepared by FSL.The effects of groove-like micro-nano structure on the microstructure,phases,degradability,biocompatibility and antibacterial properties of Mg alloy were researched.The results show that there are periodic microgrooves with different spacing and depth on the surface of the film prepared by different laser parameters.After FSL treatment,new Ag O phase and Mg O₂phase appeared in the coating.There is no significant difference in corrosion properties between samples under different laser parameters.However,its corrosion resistance is between Mg alloy and MAO coating.Due to its micro-groove structure,the corrosion resistance is weaker than that of MAO coating without femtosecond laser treatment.This groove-like micro-nano structure can appropriately reduce the degradation of Mg alloy,and the degradation rate can be controlled by changing the laser parameters.When the laser scanning speed is 50 mm/s and the scanning spacing is 0.1 mm,the sample has deeper grooves and larger surface area,and its degradation rate is also the largest,which is suitable for the growth rate of human bone.At the same time,the maximum OD value was obtained,showing good biocompatibility and strong antibacterial properties.（3）On the surface of the MAO coating prepared above,poriform micro-nano structures under different parameters were prepared by FSL.The effects of poriform micro-nano structure on the microstructure,phases,degradability,biocompatibility and antibacterial properties of Mg alloy were researched.The results show that there are through-holes with different sizes and distributions in the coating prepared under different laser parameters.This poriform micro-nano structure can also weaken the degradation of Mg alloys and the degradation rate can be controlled by changing the laser parameters.When the pore size of laser drilling is 50μm and the pore spacing is1 mm,the sample has the smallest pore size and the smallest porosity.The sample under this parameter has good hydrophilicity,and more bone-like apatite is deposited on the surface,showing good biological activity.And has the slowest degradation rate,can be suitable for human bone growth rate.It also shows good biocompatibility and excellent antibacterial properties.