Az91d Magnesium Alloy Micro-arc Oxidation Of Surface Modification And Biocompatibility

Magnesium is an exceptionally lightweight metal.With a density of 1.74 g/cm³,magnesium is 1.6 and 4.5 times less dense than aluminum and steel respectively and is very close to the density of human bone(1.75 g/cm³).The fracture toughness of magnesium is greater than ceramic biomaterials such as hydroxyapatite,while the elastic modulus and compressive yield strength of magnesium are closer to those of natural bone than is the case for other commonly used metallic implants.Moreover, magnesium is essential to human metabolism and is naturally found in bone tissue.It is the fourth most abundant cation in the human body,with an estimated 1 mol of magnesium stored in the body of a normal 70 kg adult,with approximately half of the total physiological magnesium stored in bone tissue.Magnesium is a co-factor for many enzymes,and stabilizesthe structures of DNA and RNA.Due to functional roles and presence in bone tissue,magnesium may actually have stimulatory effects on the growth of new bone tissue.Thus,it is projected that magnesium and its alloys be applied as lightweight,load bearing and good biocompatibility bone implants.However,the major drawbacks of magnesium in many applications are low corrosion resistance.So some surface treatments should be applied to meet the use of long-term implantation.Micro-arc-oxidation(MAO)is a recently developed surface treatment technology under anodic oxidation. Through MAO,in-situ-grown ceramic coating is directly formed on the surface of magnesium alloy,titanium alloy and aluminum alloy,by which its corrosion resistance,wear resistance are greatly improved in industrial environment.This research will introduce the AZ91D magnesium alloy into the field of oral implants.Micro-arc-oxidation technology will be used to AZ91D magnesium alloy surface modification,using scanning electron microscopy(SEM),X-ray diffraction(XRD),cytotoxicity expriment and some animal expriments to analysize the morphology,composition and biocompatibility of the modified alloy surface.PartⅠThe surface modification and evaluation of corrosion resistance of AZ91D magnesium alloyObjectives:To research the surface modification and corrosion resistance of new bone implant materials AZ91D magnesium alloys.Methods:Micro-arc-oxidation method was used to AZ91D magnesium alloy surface modification,using scanning electron microscopy(SEM), X-ray diffraction(XRD)analyses the modified alloy surface morphology and composition.Results:The surface of ceramic coatings is rough and porous observed by SEM.XRD analysis shows the coating is mainly composed of Mg_0.36Al_2.44O₄,MgAl₂O₄,Mg₃Al₂Si₃O₁₂,Al₁₂Mg₁₇.The corrosion resistance of modified AZ91D magnesium alloys increases obviously.Conclusions:The surface of modified AZ91D magnesium alloys suit bone implant materials and micro-arc-oxidation ceramic coatings can be effectively improved the corrosion resistance of alloys in Hank's fluids.PartⅡEvaluation of cytotoxicity of AZ91D magnesium alloy after micro-arcoxidation surface treatmentObjectives:To evaluate the cytotoxicity of magnesium alloy after micro-arc-oxidation(MAO)surface treatment.Methods:Samples of AZ91D magnesium alloy for test are made by MAO and the different concentration water extracted from the samples was obtained according to national standard.The extracts were measured by cell cultivation in vitro,MTT colorimetric to evaluate their cytotoxicity. Light absorption values(optical density,OD)were measured with enzyme-linked immunoassay instrument,cell relative growth rate(RGR)were calculated.Cytotoxicity was evaluated with 6 grade classification and OD values were analyzed statistically by ANOVA.Cell growth status was observed under microscopy.Results:L929 cells showed normal proliferation and morphology during observation periods,the cytotoxicity of AZ91D Magnesium alloy made from MAO was 0～1 grade. Conclusions:AZ91D magnesium alloy made from MAO has good biocompatibility.PartⅢEvaluation of biocompatibility of AZ91D magnesium alloy after micro-arc-oxidation surface treatmentObjectives:To evaluate the biocompatibility of AZ91D magnesium alloy after micro-arc-oxidation surface treatment.Methods:Acute toxicity test,haemolysis test,Ames tests,skin sensitization test,mucous membrane irritation were performed on the AZ91D magnesium alloy after micro-arc-oxidation surface treatment based on GB/T 16886 standard.Results:The results showed that no acute toxicity,the result of Ames test was negative,the allergenic rates and score of skin reaction were 0,no histomorphologic changes were observed in mucous membrane and the haemolysis rate of this material was 1.10%.Conclusion:The AZ91D magnesium alloy after micro-arc-oxidation surface treatment has a good biocompatibility,and is safe and nonpoisonous.