基于电接枝技术镁合金血管支架表面RGD多肽仿生膜层构建与降解行为研究

Magnesium alloy has been the research hotspot of cardiovascular stent for its excellent biocompatibility and biodegradability. However, insufficient support force caused by its fast degrade rate and weak endothelialization are main limitations for its practical application. This project intend to prepare poly vinyl coating and biomimetic coating condensed with RGD peptide consequence on Mg−Zn−Y−Nd cardiovascular stent, which has strong attachment with Mg stent and high endothelialization property. The corresponding relation, which between the property of polymeric coatings and grafting potential range, grafting time and the stand electrode potential, is systematically studied. The influence mechanism, which related to the Mg substrate, potential range and monomer structure on the structure of grafted coatings, is also revealed. Then, the research of in-vitro degradation behavior, endothelialization degree of biomimetic film, adsorption capability of blood platelet and the adhesion, and proliferation capacity to smooth muscle cells and endothelial cells, is comprehensive extended. Finally, the discussion, included the condensation style on the function express of RGD peptide consequence, the degradation law of composite film, cytocompatibility and endothelialization ability, is elucidated. By this project, the research of internal relation between electrografting, condensation reaction, degradation behavior and endothelialization, provide scientific evidence for the exploration and application of biodegradable Mg cardiovascular stent with fine endothelializaiton property.

镁合金以其优异的生物相容性和可降解性成为新一代血管支架材料的研究热点，但镁支架降解过快导致支撑力不足，同时支架表面内皮化程度较差限制了其实用化。本项目拟通过电接枝技术，在自主研发的Mg−Zn−Y−Nd合金支架表面制备乙烯基聚合物膜层与RGD多肽序列复合的高结合强度、内皮化友好的仿生膜层，系统研究电位区间、接枝时间、基底元素标准电位等与聚合物膜层性能的对应关系，揭示镁合金基体、电化学电位、有机物结构对合金表面电接枝聚合物膜层结构的影响机理；通过研究仿生膜层的体外降解行为、血小板吸附能力以及细胞黏附及增殖能力，考察膜层的降解能力和内皮化程度，揭示缩合方式对RGD多肽序列功能表达的影响，以及复合膜层的降解规律、细胞相容性和内皮化能力，最终建立电接枝-缩合反应-降解行为-内皮化的内在关系，为开发内皮化友好的可降解镁合金血管支架及其临床应用提供科学依据。

针对当前血管支架用镁合金表面有机涂层与基体间结合力较弱的问题，本项目开发了电接枝技术在生物镁合金表面的应用。研究发现，接枝电位是影响涂层质量的决定性因素。丙烯酸(AA)和丙烯酸羟乙酯(HEA)无法在镁合金表面获得完整覆盖的涂层；而甲基丙烯酸羟乙酯在较大的过电位下可形成不致密涂层，对镁合金的保护性不大；丙烯酸乙酯(EA)分子可在镁合金表面获得致密性高的涂层，可有效延缓镁合金的降解速率。.分子动力学结果显示PEA大分子在纯镁表面可形成较强吸附，而在氧化镁表面不吸附，说明只能通过阴极电接枝方法在活性较高的镁合金表面制备涂层，这与实验理论相一致； PEA涂层与镁合金间通过共价键结合，第一性原理结果表明Mg原子中的3s轨道电子与C原子2pz轨道上电子参与了新键形成。.正交实验结果显示工艺参数对PEA涂层在模拟体液(SBF)中的电化学性能的影响能力大小为：扫描速率 > 循环圈数 > 溶液浓度；优化后的样品自腐蚀电位比镁合金基体提高0.27 V，电流密度降低3个数量级；完整覆盖的PEA涂层可以有效地降低镁合金的降解速率；在接触SBF后，PEA首先发生分子链的重构，随后发生溶胀现象并以酯基水解的形式发生降解；PEA涂层具有优异的血液相容性，但对内皮细胞的分化增殖影响不明显。.在聚多巴胺(PDA)涂层的基础上制备了柠檬酸(CA)和RGD多肽的复合涂层，可明显降低镁合金降解速率、促进内皮细胞存活率。通过恒电流法在镁合金表面电聚合PCL涂层，比浸涂法制备的涂层具有好的结合力，使镁合金降解速率降低50%；以此为打底层，可有效复合功能涂层，负载肝素钠(Hep)可有效减少血小板的粘附和激活，同时负载Hep和RGD的涂层既有较好的血液相容性又能促进内皮细胞的粘附增殖。.以水杨酸钠(SS)和多巴胺(DA)的混合水溶液为电解液，采用恒电流方法，通过“镁基材阳极溶解→钝化→ePDA成膜→水杨酸根离子参与反应→涂层破坏”首次在镁合金表面制备平滑的电聚合多巴胺涂层，以解决传统自聚合涂层表面粗糙度大的问题，有效提升了镁合金表面二次改性的质量。