水性生物医用可降解聚氨酯材料用于脑组织修复研究

The brain injuries after cerebral diseases or trauma always lead to central lesion, which can not be regenerated using the existing clinical treatment, resulting in permanent disability of these patients. In this project, to overcome the dilemma, a novel extracellular matrix microenvironments for axon regeneration of central nervous system after injury will be designed and constructed based on .biodegradable waterborne polyurethanes. The mechanical properties and degradation rate of these polyurethanes scaffolds could be adjusted via employing different degradation rate of the soft segments，the ratios between soft segments and hard segments, and types of chain extenders for these polyurethanes synthesis. Moreover, neurotrophic factors, neurite outgrowth peptide IKVAV and cytidine diphosphate choline will be added into in these biodegradable waterborne polyurethane materials for preparation of adjustable pore size scaffolds by freeze-drying method. These scaffolds will provide a suitable microenvironment for nerve cell growth and axonal regeneration. These influences of polyurethane porous scaffolds on axonal regeneration, microglia, radial astrocytes and neuron cells will be investigated in vitro and in vivo. The interactions between these polyurethanes scaffolds and nerve cells in the central nervous system, and their role for axonal regeneration will be revealed. These mechanisms of polyurethane scaffolds inducing axon regeneration, and possibility of these scaffolds activating endogenous neural stem cells in adult animals, induction of differentiation into functional neurons and migration of these neurons in these polyurethanes scaffolds, and to establish functional neural circuits with the nerve tissue of original host will be deeply explored. These studies will provide a useful theoretical and scientific basis for CNS repair tissue engineering scaffold design.

因疾病或外伤造成对大脑神经的损伤导致其原有功能丧失，临床现有治疗无法对其进行修复，造成病人终身残疾。本课题提出以水性聚氨酯材料为基础，设计、构建适合受损脑神经神经修复的细胞外基质微环境。通过调节聚氨酯的组成实现支架材料的力学性能及降解速度可调；并在水性聚氨酯材料中负载神经营养因子、IKVAV多肽和胞二磷胆碱，采用冷冻干燥法制备孔径大小可调的多孔支架，为神经细胞生长提供合适的微环境。采用体内、外实验研究聚氨酯多孔支架对神经轴突再生的影响和对神经元细胞、小胶质细胞和星形胶质细胞的影响。揭示支架材料与神经细胞之间的相互作用和聚合物在中枢神经修复过程中所起到的作用。探索聚氨酯支架诱导轴突再生机理和激活成年动物内源性神经干细胞，诱导其分化成功能性的神经元以及神经元在支架中的迁移，并与宿主原有神经组织建立起功能性神经环路可能和机理，这将为中枢神经修复组织工程支架的设计提供有益的理论基础和科学依据。

中枢神经再生是再生医学的难题，由于损伤后剧烈的微环境改变及炎症反应会使损伤部位的星形胶质细胞形成致密胶质瘢痕，并进一步导致炎症长期存在，抑制内源性再生。本项目通过对水性聚氨酯化学结构进行调整，并调节聚氨酯支架的制备方法和拓扑结构，获得了不同力学性能、微孔表面结构、表面电位、降解性能及包载药物的用于神经修复的聚氨酯支架。通过构建大鼠脑运动中枢损伤模型、猪脑运动中枢损伤模型、脑出血损伤模型、外周神经损伤模型，系统研究了水性聚氨酯支架对脑损伤及外周神经的修复效果及机理。通过模拟重症脑损伤的动物实验研究发现，PEG含量在25%左右的水性聚氨酯乳液，通过冷冻铸造技术所获得的孔隙率为85-90%，孔径为100μm左右，湿态压缩模量为2-10kPa的聚氨酯支架在中枢神经损伤修复中有良好的效果。该支架内部的多孔结构、亲水性和其内部存在的自由水，使支架对多种因子具备吸附作用，能够将损伤核心部位的细胞因子转移到支架内部，使得炎症在损伤后迅速得到抑制，并形成修复性的微环境。微环境的变化使得支架与组织界面形成疏松的胶质增生带，为内源性神经干/祖细胞顺利进入支架内生长提供了桥架，促进其分化为新生神经元，形成神经网络。水性聚氨酯三维多孔支架通过调节脑损伤后病理生理学过程及损伤空间分布，促使再生信号通路如WNT信号通路激活，促进了脑损伤后内源性脑组织再生。项目的研究成果为中枢神经修复支架的设计和开发提供了坚实的理论依据和方法。此外聚氨酯支架在周围神经长节段损伤修复中同样具有良好效果。另外，着眼于我国对生物医用材料及其制品的巨大需求，研究团队实现了医用水性聚氨酯基础材料的产业化，攻克了均相、大尺寸组织工程多孔支架制备工艺的关键技术。并探索了该聚氨酯支架在口腔黏膜、全层皮肤、声带等损伤修复方面的应用，为软组织修复用聚氨酯支架真正走向临床奠定了坚实基础。

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