| Magnesium(Mg)-based biodegradable alloys and composite materials have attracted great interest from researchers in the fields of clinical medicine and materials science due to their excellent biocompatibility and mechanical properties.However,creating medical degradable magnesium alloys and magnesium matrix composites that combine corrosion resistance and antibacterial properties still faces many challenges in promoting magnesium alloys for orthopedic clinical applications on a large scale.In this study,we focused on improving the corrosion resistance of magnesium alloys while ensuring their antibacterial properties by using silver(Ag),which has a broad-spectrum antibacterial effect,and hydroxyapatite(HA),which has excellent biocompatibility,as the main media.We used a two-step method to modify the surface of the AZ31 B magnesium alloy,namely,the first step of preparing a Mg-Ag-HA composite material containing hydroxyapatite(HA)by stirring friction processing(FSP),and the second step of using a micro-arc oxidation strategy to grow a silver-containing MgO-based ceramic coating in situ on the basis of the first step,aiming to develop a novel assembly structure suitable for medical metal materials using our unique dual-process technology.XRD,SEM,EDS,TEM,XPS,electrochemical workstation,and biological performance testing methods were used to study the influence of Ag content on the microstructure,corrosion behavior,antibacterial properties,and biocompatibility of the composite material(coating precursor)and its coating.The main conclusions of this paper are as follows:(1)Using FSP technology,Mg-Ag-HA composite materials with almost equal HA content but different Ag content were prepared.The results showed that Ag particles with an average particle size of 1 μm were crushed into nanoscale particles with an average particle size of around 10 nm and dispersed in the magnesium matrix after 10 passes of FSP.(2)The introduction of a small amount of Ag into the composite material can improve its corrosion resistance,but as the silver content gradually increases,the galvanic corrosion effect intensifies and the corrosion resistance of the composite material decreases.Thanks to the release of Ag ions from the nanoscale Ag particles,even the lowest Ag-containing composite material,FAg0.1,exhibits antibacterial properties above 99%.Compared with the Mg-based material(BM),the addition of a small amount of Ag can improve biocompatibility,but as the silver content gradually increases,cytotoxicity increases.(3)Using MAO,layers of Ag-containing MgO-based ceramic coating were in-situ generated on the Mg-Ag-HA composite material.The results showed that the elements from the substrate and electrolyte could be incorporated into the coatings.The HA from the precursor in the coating promoted the growth and formation of the coating,while the size of the Ag particles from the precursor in the coating remained unchanged.The variation in Ag content in the precursor led to a phase transformation in the microstructure of the coating,and the proportion of MgO phase in the coating decreased as the galvanic corrosion became stronger.(4)The corrosion resistance of the coating was determined by both the proportion of MgO phase and the variation in Ag content,with the latter being dominant.When the Ag content in the precursor was increased by less than 1%,the corrosion resistance of the coating gradually improved,and the MFAg1.0 had the best corrosion resistance.However,when the Ag content in the precursor was increased beyond 1%,the corrosion resistance of the coating gradually decreased.The Ag particles from the precursor in the coating still endowed the coating with excellent antibacterial properties,with even MFAg0.1 containing silver having over 90% antibacterial effectiveness.The addition of a small amount of silver and the introduction of HA enhanced the biocompatibility of the coating,but with the gradual increase of silver content,the cytotoxicity increased. |
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