| In order to improve the corrosion resistance of medical Mg-1Zn-0.2Ca-1MgO alloy and meet the clinical medical requirements of bone repair implant materials,micro-arc oxidation ceramic coatings were prepared on the surface of the alloy by micro-arc oxidation process in a mixed electrolyte of silicic acid and phosphoric acid.The effects of different forward voltages on the micro-arc oxidation coating of Mg1Zn-0.2Ca-1MgO alloy were systematically analyzed.In order to further improve the osteogenic properties of magnesium-based alloys,polydopamine was grown on the surface of micro-arc oxidation coating by immersion method.The effects of different immersion time on the microstructure and properties of MAO coating were discussed.The inclusion complex of β-CD and NG was synthesized by freeze-drying method.The changes of tissue properties of PDA-β-CD/NG coating at different inclusion complex concentrations and the release of naringin in simulated body fluid were studied.In order to protect the MAO coating from the destruction of dopamine,polycaprolactone was bonded to the micro-arc oxidation coating by impregnation method,and then the drug loading treatment was carried out again.Through the study of phase,microstructure,corrosion resistance and bone formation of polycaprolactone drug-loaded coating,the following conclusions are drawn:(1) The MAO samples prepared at different forward voltages during micro-arc oxidation are mainly composed of Mg,MgO,Mg2SiO4 and Ca3(PO4)2.The surface and cross-section microstructure results of the coating show that when the voltage increases from 450 V to 550 V,the coating holes are gradually filled,the compactness is improved,and the corrosion resistance of the sample is improved.The results of electrochemical and hydrogen evolution experiments show that the F3 coating has the largest corrosion potential:-1.318 V,the lowest corrosion current density:1.808 μA/cm2 and the lowest annual corrosion rate:0.09 mm/y.Continue to increase the voltage (600 V) will cause the generation of large pores,and more defects appear in the cross section,which aggravates the destruction of corrosive ions.(2) When the MAO sample is immersed in dopamine buffer,the coating will change with the extension of immersion time.When the soaking time reaches 10 h,the porosity reaches the lowest (13.62 %),the coating is the densest,and the coating thickness reaches 40 μm.Electrochemical and hydrogen evolution experiments show that the corrosion resistance of the coating increases first and then decreases with the immersion time,and has the best corrosion resistance when the immersion time is 10 h.(3) After the inclusion complex drug was added to the dopamine buffer solution,the coating increased from 50 μm to 57 μm with the increase of concentration,and the compactness was also gradually improved.When the concentration reaches 2 wt %,the electrochemical results show that the coating has the highest corrosion potential (1.345 V) and the lowest corrosion current density (2.162 μA/cm2).(4) With the increase of polycaprolactone concentration,the ceramic phase composition of the coating remained unchanged,but the characteristic peak of polycaprolactone at 20-25°was enhanced,and the corrosion resistance of the coating was improved.After drug loading treatment,the NG release amount of PCL drugloaded coating in simulated body fluid was measured by linear regression equation,which was equivalent to that of MAO drug-loaded coating,indicating that the addition of PCL did not affect the release of NG in vivo.The results of cell experiments showed that the magnesium alloy released Mg2+ in the later stage and caused certain cytotoxicity,and the MAO drug-loaded coating had the best cell activity in the later stage.Since NG has the ability to induce the expression of osteogenic factors and promote bone formation,immunoblotting also shows that the MAO drug-loaded coating has the best osteogenic performance. |
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