功能型生物可降解聚氨酯小口径人工血管的构建及促原位再生修复血管损伤的效果和机制

Post-transplantational restenosis and thrombosis are the main problems which limit the application of small-diameter artificial blood vessel in clinical widely used, and have not been resolved effectively due to the fact that the current product cannot be rapidly endothelialized or does not have appropriate mechanical strength, and it is not important to pay attention to the function of the outer layer of blood vessels and the lack of optimal materials. We have designed and synthesized biodegradable polyurethane which can be highly chemically modified. The biodegradable polyurethane mechanical properties and degeneration speeds are adjustable, which provides a new idea for the preparation of artificial blood vessels. With the original researching basis, we will combine the electrospinning and thermal induced phase separation to prepare a novel functionalized biodegradable polyurethane bilayer small-diameter artificial blood vessel. First, the biodegradable polyurethane has better compliance, toughness and elasticity. Second, REDV could capture endothelial progenitor cells, preventing platelet adhesion and promoting rapid internalization as well as inhibit inflammatory reaction, and improve microenvironment of transplanted artificial blood vessel. In addition to this, the oriented topological microstructure in the outer layer can induce the phenotype of hVSMCs will switch to a contraction type in vivo, which is more conducive to the formation of endothelial layer. The hemodynamic status, restenosis rate, endothelium coverage and local thrombosis of the transplanted artificial blood vessel in rabbit carotid artery will be characterized via computer simulation of fluid dynamics, imaging technology, arteriography technology, optical microscope and SEM. This research will provide the theoretical foundation and experimental evidence for artificial blood vessel in fundamental research and clinical application.

小口径人工血管移植后再狭窄和血栓形成限制其临床应用，主要是不能快速内皮化、缺乏适当力学强度，未注重血管外层功能构建和缺乏最佳材料是关键。我们前期设计、合成可高效化学修饰的生物可降解聚氨酯，其力学性能和降解周期可调，为制备人工血管提供新思路。本课题采用静电纺丝和热致相分离联合技术制备功能型生物可降解聚氨酯小口径人工血管，在材料方面改善其生物相容性和力学性能，在结构上内、外层并重，其内层为修饰有PEG2k、肝素、REDV的纳米纤维，可俘获EPCs促进快速内皮化、抗血小板粘附、抑制炎症反应，外层为取向拓扑微结构，可重塑血管组织力学而稳定血流、诱导hVSMCs表型转变而利于内皮层形成；同时制作兔颈动脉血管移植模型，用计算机模拟流体力学分析移植血管血流动力学，用动脉造影和组织学检查等评价血管再狭窄率、内皮覆盖及局部血栓情况。本研究有望构建一种可临床应用的小口径人工血管，并为其提供实验依据。

由于缺乏最佳原材料，且小口径人工血管未注重血管内外层功能协同构建，造成移植后不能快速内皮化、力学顺应性匹配不佳，最终形成的狭窄和血栓限制了其临床应用。本项目实现了生物可降解聚氨酯PEEUU-NH2、PEEUU的可控合成，合成产率稳定保持在90%左右，合成的弹性体具有优良的可纺性和高密度化学接枝位点；采用静电纺和热致相分离联合技术制备纳米纤维小口径人工血管，理化测试、拉伸力学测试和体外降解研究结果表明，基于HDI、LDI、PEG600合成的纳米纤维具有不同的结晶性能，表现出不一样的热学、力学和降解特性。软段中PEG600的存在使得合成的聚合物更容易结晶；LDI型聚氨酯的热稳定性要强于HDI型；软段中PEG600的存在以及合成单体HDI换成LDI都会使聚合物的可纺性降低，同时纳米纤维的应力和应变都明显减小，但仍能满足血管移植的要求。另一方面，PEG600的加入使得纤维膜在24周的降解率从18%增加到70%，促进了纤维材料的降解；同时，我们还发现材料的亲水性和纤维的规整、均一形貌，对内皮细胞增殖、迁移有积极影响。在此基础上，我们将电纺的PEUU纤维氨基化，再通过酰胺化组装，将PEG和肝素小分子接枝到PEUU纤维表面，构建了一种高效功能化修饰的纳米纤维小口径血管支架PEUU@PEG2k-Hep，兔颈动脉移植实验结果发现该血管能够一周快速内皮化；将PEUU弹性体与明胶共混纺丝，制备了一种纳米纤维小血管，兔颈动脉移植实验结果发现这种血管具有良好的力学顺应性，完全能够通过材料与自体组织力学匹配性调控避免移植后急性栓塞发生。将合成的亲水性得到改进的PEEUU弹性体溶解后浇铸到含有管状织物的模具中，经过相分离和脱模处理制备了具有仿生细胞外基质结构的三维多孔织物增强的小直径管状移植物（PPTG），具有与自体血管匹配的力学性能和稳定的血液相容性，这种血管网不易发生阻塞。通过材料的选择、结构的优化设计与体内外的反复试验。研制的功能型人工小血管能够一定程度上解决小口径人工血管血栓/再狭窄的问题，为人工血管研究领域提供了新的理论基础和新的策略。

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