Preparation And Properties Of MAO/Silane-BPs Multifunctional Coatings On Magnesium Alloy For Bone Implantation

Magnesium alloys were considered as materials with great development potential for degradable bone implant devices owning to their biodegradability,great mechanical properties and biocompatibility.However,the rapid degradation rate of Magnesium alloys limits its wide application in the biomedical field.Bisphosphonates（BPs）are commercially available drugs for the treatment of bone disorders,inhibiting bone resorption and promoting the growth of osteoblasts.In this work,a strategy was proposed to prepare the bio-functionalized anticorrosion coating by loading commercial drugs that have an inhibition effect on Mg corrosion.ETN can not only inhibit the degradation of magnesium alloys,but also have biological functions.This provides a new idea for the design of multifunctional coatings on Mg alloy for biomedical applications.It is of great significance to promote their applications in the field of orthopedics.In this paper,the effects of two bisphosphonates,etidronate（ETN）and alendronate（ALN）,on the degradation behavior of ZE21C Magnesium alloy in simulated body fluids were investigated by static weight loss test and electrochemical test.Subsequently,the ETN-loaded functional composite coating was prepared on the surface of ZE21C Magnesium alloy by micro-arc oxidation and silanization treatment.The effect of ETN on the structure,corrosion resistance and biocompatibility of composite coatings was systematically investigated.The degradation mechanism of the composite coating and the corrosion inhibition mechanism of ETN were discussed.The experimental results show that ETN and ALN can significantly slow down the corrosion rate of ZE21C Magnesium alloy in simulated body fluid.The corrosion inhibition efficiency of ETN and ALN on magnesium alloy can reach 58.57%and 90.91%at the highest.The reason is that the phosphonic acid groups in ETN and ALN undergo chelation reaction with Mg²⁺generated during the degradation of magnesium,and the formed stable chelate precipitates on the surface of the alloy to inhibit the corrosion of magnesium.The preparation process of the composite coating was optimized by investigating the surface morphology and corrosion resistance,the optimal preparation process is as follows:300 V of MAO,2 h alkaline heating on the MAO surface,8 h of silane hydrolysis,30 min of silane solution dip coating,the loading of ETN inhibitor in the coating is 1 mmol·L^-1.The results of SEM,FTIR and XPS indicated that the silane coating was successfully prepared on the MAO surface and covalently bonded to the MAO substrate;ETN was successfully loaded in the composite coating,and the loading of ETN did not change the morphology,thickness and structure of the coating.The contact angle experiment indicated that the water contact angle of the MAO/PAPTMS-ETN composite coating is 45°,which with great hydrophilic properties.The micro-scratch test indicated that the MAO/PAPTMS-ETN composite coating has great bonding strength.Atomic force microscopy（AFM）results indicated that the roughness of MAO/PAPTMS and MAO/PAPTMS-ETN composite coatings was increased compared with the Magnesium substrate,the roughness of the coatings was still at the nanometer level which can facilitate the occurrence of osseointegration.The polarization curve results showed that the corrosion current density(I_corr)of the MAO/PAPTMS-ETN composite coating is one order of magnitude and two orders of magnitude lower than that of the MAO/PAPTMS coating and the Magnesium substrate,respectively.In a 7-days hydrogen evolution experiment,the MAO/PAPTMS-ETN composite coating exhibited long-term anticorrosion performance in simulated body fluids.Cell culture experiments indicated that the ETN-containing composite coating have great osteogenic properties and promote the adhesion and proliferation of MC3T3-E1 cells.The hemolysis rate of the coating samples was lower than 5%,and the addition of ETN reduced the hemolysis rate of the composite coating to 0.37±0.1320%.