Preparation Of Zinc-containing Coating Developed On Medical Magnesium Alloy And Investigation On In Vitro Biocompatibility

As the lightest structural metal material,magnesium alloy has the similar density and Young’s modulus to human bone,which can effectively alleviate the stress shielding effect.Magnesium alloy is considered as a revolutionary degradable metal implant material.Although magnesium alloy can be used as a degradable implant material to avoid secondary surgery,the degradation rate in the living body is too fast.Micro-arc oxidation（MAO）is an effective surface treatment technology to improve the performance of magnesium alloy.In this paper,EDTA-ZnNa₂,which has excellent solubility in water,was selected as the zinc-containing electrolyte.In the alkaline and neutral solutions,the electrolyte composition and electrical parameters were adjusted in order to improve the corrosion resistance of magnesium alloy.The beneficial trace element zinc was introduced into the coating to improve its biocompatibility and achieve surface layer functionalization.This paper mainly carries out the following three aspects of work:Firstly,the effects of sodium silicate and EDTA-ZnNa₂ concentrations on surface morphology,chemical composition,phase structure and corrosion resistance of MAO coatings were investigated.The entrance mechanism of Si and Zn into MAO coatings was discussed.The results show that in a certain concentration range,sodium silicate can increase the uniformity,thickness,corrosion resistance and Si content of MAO coating,while the excessive concentration is detrimental to coating thickness and corrosion resistance.EDTA-ZnNa₂ is a corrosive agent of magnesium alloy.When EDTA-ZnNa₂ concentration is low,the increased EDTA-ZnNa₂ can improve the Zn content in MAO coating.However,with the increase of EDTA-ZnNa₂ concentration,the corrosion resistance of MAO coating decreases.In addition,the coating integrity may be affected and even anodic coating can’t develop on magnesium alloy.Secondly,in the neutral solution containing ammonium salt,the effects of process parameters on the corrosion resistance and zinc content of the oxide film were investigated by an orthogonal experiment.The results show that in the neutral electrolyte,one-step MAO treatment can successfully prepare a Zn-containing coating with the highest zinc content 4.12 wt.%on WE43 magnesium alloy.The influencing sequence of processing factors on Zn content in anodic coating is EDTA-ZnNa₂>NH₄HF₂>Phytic acid>H₃PO₄,while the rank on I_corr of MAO treated samples is EDTA-ZnNa₂>NH₄HF₂>H₃PO₄>Phytic acid.Within a certain treating time range,the prolonged treatment time can gradually decreases the Zn content of anodic coating and slightly increases the coating thickness.Thirdly,in a neutral solution,the influences of EDTA-ZnNa₂ concentration on surface morphology,chemical composition,corrosion resistance and biocompatibility of Zn-containing MAO coatings were investigated.The results show that in a certain range,with the increase of EDTA-ZnNa₂ concentration,the corrosion resistance of MAO coating is slightly decreased,and the Zn content in anodic coating is increased.The prepared zinc-containing MAO coatings have good biocompatibility.The MAO coatings have good cell adhesion and do not show obvious cytotoxicity.The cell proliferation and differentiation on the surface coatings are promoted.Among them,when added EDTA-ZnNa₂ is 6 g/L,the fabricated MAO treated sample achieves the best osteoblast differentiation.