医用镁合金微弧氧化工艺研究进展

从火花放电方面归纳整理了镁合金微弧氧化膜层的形成机理，并分析了膜层结构。在此基础上，结合国内外研究现状，阐述了预处理、电解质和添加剂以及电参数（电压、电流模式和脉冲频率）和封孔技术对镁合金微弧氧化膜层耐蚀性和生物相容性的影响。着重分析了电解质和添加剂的种类、浓度对膜层和生物性能的影响机制，其中电解质包括碱性硅酸盐和磷酸盐电解液等，添加剂包括甘油、氟化物、羟基磷灰石和纳米粒子等。研究发现，碱性磷酸盐电解质的加入可以降低膜层腐蚀速率，促进骨整合和细胞附着过程，羟基磷灰石、Ca、P等具有生物活性和对人体有益的粒子作为添加剂加入，可以显著提高膜层的耐蚀性和生物相容性。最后，基于研究现状，对镁合金微弧氧化技术在生物医用方面的发展进行了展望。

Research Progress on Micro-arc Oxidation of Medical Magnesium Alloy

Magnesium alloy is a highly promising biodegradable metal material for biomedical use, with the advantages of density and elastic modulus similar to those of human bone, reducing the stress-shading effect of bone implants, avoiding osteoporosis and promoting new bone growth. In addition, magnesium alloy also has good machinability, castability and fracture toughness at high temperature, which is more advantageous than other materials for biomedical materials. However, the defects of magnesium alloy as an implant material are that its corrosion rate in body fluids is too fast. Therefore, degradation rate is not easy to control, and the mechanical properties of the implant are greatly reduced, which is not enough to support human bone healing. To address this issue, the surface treatment is necessary to achieve degradation control and improve mechanical properties, corrosion resistance, biocompatibility and antibacterial properties of magnesium alloys. Among the surface technologies, micro-arc oxidation has the advantages of simple pretreatment, uniform film formation, high bonding strength with matrix and enhanced biocompatibility of magnesium alloys. Currently, there are few reviews on micro-arc oxidation technology of magnesium alloys. In this work, the formation mechanism and structure of micro-arc oxide film on magnesium alloy were summarized from the perspective of spark discharge theory. On this basis, from the classification of the affecting parameters of micro-arc oxidation, the effects of pretreatment, electrolyte, additives, electrical parameters (voltage, current mode and pulse frequency) and sealing technology on the corrosion resistance and biocompatibility of magnesium alloy micro-arc oxidation film were expounded combined with the research status in China and abroad. Thus, the research progress of micro-arc oxidation technology for medical magnesium alloys was introduced by studying the affecting parameters. Herein, the work mainly focused on the analysis of the type and concentration of electrolytes and additives on the membrane and biological properties of the mechanism, in which electrolytes included alkaline silicate and phosphate electrolyte and additives included glycerol, fluoride, hydroxyapatite and nanoparticles, etc. It was found that the addition of alkaline phosphate electrolyte could reduce the corrosion rate of the film and promote the process of bone integration and cell attachment. Besides, hydroxyapatite, Ca, P and other bioactive particles as additives could significantly improve the corrosion resistance and biocompatibility of the film. Last but not least, according to the further research, it was found that the affecting factors of process parameters on the micro-arc oxide film layer were not single linear. No matter the process parameters were lower than the minimum value or higher than the maximum value, the performance of the film would be damaged to some extent. From this perspective, it is necessary for researchers to strike an optimal balance between corrosion resistance and biocompatibility. At present, compared with other surface technologies, there is a lack of comprehensive and profound explanation of its film formation mechanism due to the complexity of micro-arc oxidation. Therefore, it is urgent to establish a rich and scientific mechanism research system. Finally, in view of the existing problems, the application of micro-arc oxidation in medical magnesium alloys is prospected.