镁合金表面杂化涂层的制备、变形机理和生物降解的研究

Coating modified magnesium alloys have been considered as the revolutionary biodegradable materials used as orthopedic implants due to their desirable mechanical properties and biocompatibility. However, the implants have to shoulder a constant stress or cyclic stress when they serve inside the human body, cracking and peeling off of the coating from magnesium substrate due to the elastic/plastic deformation mismatching between coatings and magnesium alloy substrates lead to fast degradation, and hereby limit the clinical application. In this project, based on the structural characteristics of phytic acid and silanes, and the easily chelating of phytic acid with magnesium, hybrid coatings were synthesized in situ on magnesium alloys using chemical conversion and solvothermal methods to improve the deformation matching of magnesium alloy substrate to coatings. In order to achieve the controllable synthesis of hybrid coating on magnesium alloys, and then explore the constitutive relation and deformation mechanism of hybrid coating deformation, the process of the dissociation, hydrolysis, polycondensation of phytic acid and silanes were investigated in this study. Meanwhile, the degradation behavior and the biological properties of the coated magnesium alloys in vitro and in vivo were also studied, and the influence of degradation behavior, composition and microstructure changes of the coatings under the applied pressure on the biological properties is elaborated in a systematic and scientific way, aiming at achieving the hybrid coatings coated magnesium alloys with good biological properties and controllable degradation rate. The proposed design ideal and manipulation technology of the controllable deformation coating on magnesium alloy is therefore expect to pave the way to the further investigation of the surface functional optimization of medical alloys.

涂层改性镁合金有望成为重要的可降解吸收骨植入材料，但在生理环境中，因涂层与镁合金基体的弹/塑性变形不匹配，在体内受力条件下，涂层开裂、脱落，致使植入体的降解速度与骨组织的再生进程失配。本项目利用植酸和硅烷的结构特点，以及植酸与镁离子的螯合作用，将化学转化和溶剂热法相结合在镁合金上原位合成杂化涂层，改善涂层与镁合金的变形匹配性。重点研究体系中解离、水解和缩聚过程及其产物的调控因素，从而设计涂层的组成和结构，实现涂层的可控合成，进而调节杂化涂层的变形性能和功能特性，探究杂化涂层的本构关系和变形机理。同时，开展涂层改性镁合金的体内外降解和生物学研究。系统阐明体内受力条件下材料降解、涂层组成和结构变化对材料生物学的影响规律，从而获得具有良好生物性能、可控降解的杂化涂层改性镁合金材料。本项目提出的镁合金上可控变形杂化涂层的设计思路和制备技术，为进一步研究医用金属或合金表面的生物功能复合化奠定了基础。

镁及其合金作为一种医用金属材料，因其具有与自然骨相匹配的力学性能，可降解及良好的生物相容性，有望成为新一代可降解硬组织修复植入材料。但在人体环境内因Cl−的存在使其降解速率过快，导致其力学性能过早失效，不能提供长期有效的力学支撑，限制了其临床应用。本项目利用植酸和硅烷的结构特点，将化学转化法和水热法、微波液相法相结合，在镁合金上原位合成了系列杂化涂层。研究了植酸、硅烷与镁离子的螯合作用，以及杂化涂层构建的调控因素和形成机理。重点研究了杂化涂层在受力条件下材料的降解、涂层组成和结构变化，及其对材料生物学的影响规律。.在镁合金上成功制备出表面形貌均匀、致密，与镁合金基体结合紧密的多种杂化和复合涂层，如植酸/γ-APS硅烷、植酸/羟基磷灰石、β-TCMP/羟基磷灰石等涂层。植酸/羟基磷灰石杂化涂层与基体的结合强度达到24.3 ± 1.7 MPa，主要是源于植酸与镁合金间强烈的螯合作用，以及水热过程中缺陷的原位修复。β-TCMP/羟基磷灰石复合涂层具有优异的耐蚀性能，其交流阻抗值和自腐蚀电流密度分别为1197 kΩ.cm2和0.043 μA/cm2，为无涂层包覆的镁合金试样的2000倍和1/1000。模拟体内受力环境，研究了在压应力作用下杂化涂层包覆镁合金试样的腐蚀行为，力学性能变化规律。前期受力试样的腐蚀速率更快，但在第6 天后，受力条件下试样的腐蚀速率小于或等于不加压的条件，可能与裂纹的修复有关。.在体外细胞实验中，杂化涂层促进了材料对培养基中蛋白质的吸附，有利于成骨细胞在涂层表面的黏附和增殖，以及骨相关蛋白的表达。体内大白兔动物实验表明，杂化和复合涂层包覆的镁合金骨板和骨钉具有更优异的成骨性能，其耐腐蚀性能满足一般骨组织修复所需的降解周期3-6个月。本研究成果可为可降解骨修复镁合金器件的开发提供大量的实验数据和丰富的理论依据，对临床应用具有重要的指导意义。