| Artificial bone implant materials are the key to treat orthopedic diseases such as fractures and bone defects.Biodegradable magnesium alloy has the similar density and elastic modulus to human bone,and also can be completely degraded in vivo to avoid secondary surgery.It has become the most ideal candidate for bone implant materials.However,magnesium alloy presents poor corrosion resistance in body fluids,making it difficult to satisfy continuous load-bearing requirements.Its corrosion usually causes local alkalization and hydrogen evolution,causing tissue necrosis and endangering the health of the body.Related research pointed out that,coatings which combine corrosion protection and good biocompatibility show great potential in improving the properties of magnesium alloy.In this paper,a polydopamine/hydroxyapatite?PDA/HAp?composite coating was successfully prepared on degradable AZ31 magnesium alloy substrate by oxidative self-polymerization and hydrothermal method.The composite coating showed distinguished anti-corrosion performance and biocompatibility.The specific contents and results of this study are as follows:?1?By optimizing the solvent selection,PDA coating was prepared in ethanol solution.The results of scanning electron microscope?SEM?,energy dispersive spectroscopy?EDS?and Fourier transform infrared spectroscopy?FTIR?confirmed the successful preparation of PDA coating.The PDA film prepared in ethanol solution reduced corrosion of the substrate and improved the morphology of the coating.Results of atomic force microscope?AFM?showed that the surface roughness of PDA coating decreased from 13.36 nm to 9.10 nm.At the same time,PDA coating significantly improved the hydrophilicity of the substrate.Electrochemical test showed that the corrosion current density(Icorr)decreased from 6.32×10-5 A/cm2 to 8.64×10-6 A/cm2,and the corrosion protection efficiency was 86.4%.After soaking in SBF for 7 days,the composition of Ca and P on the surface of PDA coating increased,which could induce the deposition of calcium phosphate.?2?HAp coating was prepared by hydrothermal method on the basis of PDA layer.The formation mechanism of PDA/HAp composite coating is as follows:PDA coating can be used as a secondary reaction platform,the rich catechol groups on the surface actively combine with Ca2+,increase Ca2+supersaturation at the interface,and promote HAp nucleation.That is,PDA can induce HAp coating formation.SEM and EDS results showed that the HAp coating induced by PDA layer has a more compact structure.Tensile shear test results showed that PDA inner layer can improve the binding strength of HAp outer layer.The corrosion current density of PDA/HAp composite coating further decreased to 2.04×10-7 A/cm2,and the protection efficiency of the composite coating reached 99.6%.The results of immersion test showed that the macro and micro morphology of the composite coating have not changed significantly within 15 days.PDA/HAp composite coating did not cause local alkalization and severe hydrogen evolution.?3?The blood compatibility and cell compatibility of the PDA/HAp composite coating were evaluated.The hemolysis rate of PDA/HAp composite coating was only 0.51%.The cytotoxicity results showed that the composite coating extract has no toxic effect on the cells.Ca and P from PDA/HAp promoted the proliferation of MC3T3-E1 cells at 100%extract concentration.Compared with other samples,the most cells were observed on the surface of PDA/HAp coating,and the cell morphology was the most complete.The pseudopodia structure was differentiated,which proved that PDA/HAp coating has the biological function of inducing osteoblast adhesion. |
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