镁合金纳米晶微弧氧化复合表层的构建及其腐蚀、生物学行为研究

Conventional Mg alloys can’t meet the requirements of application for biomaterials due to their poor corrosion resistance. To achieve modification for corrosion resistance and bio-performance of Mg alloys, micro-arc oxidation (MAO) treatment has been a hot area of research. However, some issues deteriorating the protection efficiency of MAO coatings have limited their extensive applications, such as lower adhesive strength, inhomogeneous thickness as well as occurrence of macroscopic crack caused by coarse microstructure or inhomogenous element distribution of the Mg substrate. In our project, for the purpose of improving the comprehensive properties (e.g., corrosion resistance and biocompatibility) through microstructure design of both Mg matrix and surface coating, a nanocrystalline (NC) layer was firstly fabricated on Mg alloys surface by adopting sliding friction treatment, then a MAO outer layer grew on NC surface and finally the modified NC-MAO duplex layer was obtained. The microstructure, forming mechanism, degradation as well as biocompatibility of NC-MAO duplex layer will be studied, the exact relationship and corresponding regulation mechanism between coating microstructure, degradation as well as biological behavior will also be explored. This work not only provides design criteria and manufacturing principle for high quality MAO coating, but also provides theoretical direction for designing degradable implants as well as their performance optimization.

传统镁合金耐蚀性差不能满足医用材料的使用要求，对镁合金进行微弧氧化处理以改善耐蚀和生物性能一直是研究热点，但制约其应用的关键问题是：镁合金基体组织粗大或成分不均匀造成微弧氧化涂层结合强度低、厚度不均或产生宏观裂纹而降低防护效果。本项目拟利用滑动摩擦技术在镁合金表面制备纳米晶表层，再采用微弧氧化技术对纳米晶表层进行微结构重构，设计纳米化-微弧氧化复合改性层，通过基体与涂层的组织结构设计来实现耐蚀性和生物相容性的综合优化。研究纳米化-微弧氧化复合改性层的组织结构，揭示涂层形成机制并阐明其降解行为、生物相容性，探讨涂层结构与化学特性等与降解、生物学行为之间的依存关系及相关调控机制。此项工作能为性能优异的微弧氧化涂层材料的开发提供设计准则与制备原理，并为可降解植入器械设计和性能的进一步优化提供反馈和理论指导。

镁和镁合金的可降解特性及良好的力学相容性使其成为极具发展潜力的新型硬组织植入材料。然而，镁材料较差的耐蚀性限制了其在生物医学领域的广泛应用。因此，必须对镁合金进行改性处理以保障其在服役期间的生物安全性及生物相容性。.微弧氧化（micro-arc oxidation，MAO）是简单高效的镁合金表面处理技术，但MAO涂层存在孔隙率过高、厚度较小等问题。传统的解决方法主要是调整电参数和电解液配方或者进行封孔后处理，而实际上基体的结构对MAO涂层的质量起着至关重要的作用，因此，本项目提出在微弧氧化处理之前，采用滑动摩擦技术（sliding friction treatment，SFT）分别对纯镁和AZ31合金进行表面预处理，以改变基体的微观结构。通过SFT和MAO技术相结合的方法制备优质MAO涂层，为设计可降解镁基植入材料提供了新思路。本项目主要研究结果如下：.采用SFT技术成功在纯镁和AZ31合金表面制备出800 μm厚的超厚变形层，纯镁的最表层晶粒细化至细晶级（fine grain，FG）；AZ31合金最表层晶粒细化至纳米级（nanocrystalline，NC）。腐蚀实验结果表明SFT处理后纯镁和AZ31合金的耐蚀性能均得到显著提升。.在原始粗晶（coarse grain，CG）和细晶基体表面成功制备了MAO涂层，研究发现微弧氧化处理后，纯镁FG层和AZ31 NC层均成功保留下来。FG-MAO和NC-MAO涂层与原始粗晶基体上制备的CG-MAO涂层的化学组成没有明显差别，但FG-MAO和NC-MAO涂层的表面粗糙度和孔隙率相对更低，涂层的厚度显著增加，且涂层与基体的结合性能显著增强。.电化学测试及浸泡实验均表明复合处理FG-MAO和NC-MAO样品的耐蚀性得到明显改善，表明SFT预处理技术有利于制备出更优质的MAO涂层。.采用细胞增殖、溶血试验、血小板粘附试验对CG-MAO和NC-MAO样品进行了生物相容性研究。直接法试验结果表明NC-MAO涂层表面粘附的细胞呈现多触角形态，而CG-MAO涂层表面的细胞呈现不健康的圆形特征；间接法试验结果表明NC-MAO涂层比CG-MAO涂层更能促进成骨细胞的粘附和增殖。此外，溶血试验和血小板粘附试验结果表明NC-MAO涂层具有良好的血液相容性。NC-MAO涂层生物相容性的提高主要得益于其优质的涂层结构和优异的耐蚀性。