Study On The Inhibition Of Bacterial Infection And Osteogenesis By Self-Assembled Multifunctional Composite Coatings On Magnesium Alloy Surfaces

ObjectiveMagnesium(Mg)and its alloys have shown strong promise for repairing load-bearing areas and repairing sizeable segmental bone defects due to their unique biological features such as good biocompatibility,biodegradability,elastic modulus comparable to bone,and osteoconductivity.However,the rapid degradation of magnesium,limited antimicrobial capacity,and lack of sufficient osteogenic activity ultimately lead to implant failure.Therefore,improving magnesium implants’ corrosion resistance,osteogenic activity,and antimicrobial ability is critical in promoting their large-scale clinical application.In this study,we constructed polydopamine@gentamicin/calcium-phosphorus composite coatings by self-assembly on the hydrothermally pretreated magnesium matrix surface using co-deposition and polydopamine(PDA)-induced mineralization and investigated in detail the corrosion resistance,antibacterial properties and osteogenic activity of the magnesium matrix composites in vitro and in vivo.To explore its application prospects as a material for the repair of infected bone defects.This study provides an effective surface modification strategy for developing multifunctional magnesium-based implants,thus expanding the progress and development of their applications in bone defect repair.Methods1.AZ31 magnesium alloy was hydrothermally treated to obtain AZ31-OH,which was then immersed in a mixture of dopamine(DA)and gentamicin(G)solution and calcium-phosphorus(CaP)solution to prepare the composite coating,respectively.The obtained samples were divided into AZ31-P,AZ31-P@G,AZ31-P/CaP,and AZ31-P@G/CaP.2.The surface and cross-sectional morphology and elemental composition of each group of materials were analyzed by Scanning Electron Microscope(SEM),Energy Dispersive Spectroscopy(EDS),X-Ray Diffractometer(XRD),and Fourier Transform Infrared Spectrometer(FTIR)to examine the composition and structure of composite coatings on the surface of the materials.Simulated Body Fluid(SBF)immersion method and electrochemical tests were performed to analyze the composite materials’ corrosion behavior,drug release behavior,and degradation rate.3.The composite materials of each group were co-cultured with Staphylococcus aureus(S.aureus)and Escherichia coli(E.coli).SEM and inhibition circle assay evaluated the antibacterial properties of the composite coatings.The effect of each composite on the proliferation viability and adhesion behavior of mouse embryo osteoblast precursor cells(MC3T3-E1)was examined by the CCK-8 method,rhodamine-labeled ghost pen cyclic peptide staining,and SEM.Alkaline phosphatase(ALP)staining and activity assay were performed to assess the expression of ALP in each group.4.To establish a model of infected bone defects in rats,each group of composite materials was implanted in the corresponding location,the rats were euthanized,and the materials were taken at the specified time points.The in vivo resistance of the materials to infection was assessed by the coating plate method and Hematoxylin-eosin(H&E)staining.The collected specimens were subjected to microcomputed tomography(Micro-CT)with methylene blue/magenta staining to detect the osteogenesis of each group of materials at the site of bone defects and the degradation of the materials.H&E staining was performed to observe the pathological changes in rat organs to assess the biosafety of the materials in vivo.Results1.SEM shows that the surface of AZ31-P@G/CaP has porous,homogeneous lamellar crystals.The cross-sectional SEM results also show good continuity between the coating and the substrate,with a tighter bond.In vitro immersion and electrochemical experiments showed that AZ31-P@G/CaP exhibited better corrosion resistance and structural stability than the control group and had a more extended drug release profile.2.In vitro inhibition circle experiments and SEM observations showed that AZ31-P@G and AZ31-P@G/CaP exhibited good inhibition properties.Cellular assay results showed that AZ31-P@G/CaP significantly promoted the proliferation,adhesion,and osteogenic differentiation of MC3T3-E1 compared to the control group.3.In vivo experiments showed that the AZ31-P@G/CaP implant had good antibacterial properties in the early stage,significantly promoted bone regeneration under infected conditions,and had good corrosion resistance.No significant pathological changes were observed in the vital organs of the rats after implantation of the composite.Conclusions1.The P@G/CaP composite coating significantly improves the corrosion resistance of AZ31 magnesium alloy and has an excellent interfacial bonding ability with the magnesium alloy matrix.2.AZ31-P@G/CaP has good in vitro cytocompatibility and osteogenic differentiation and shows a strong antibacterial effect against Gram-positive and Gram-negative bacteria.In addition,AZ31-P@G/CaP exhibited excellent bactericidal and osteogenic effects in the in vivo infection setting.