可降解温敏型可注射水凝胶的设计、构建及其在关节软骨缺损修复中的作用研究

Cartilage defect caused by congenital abnormalities or disease and trauma is of great clinical consequence, given the limited intrinsic healing potential of the tissue. The rapidly emerging field of tissue engineering holds great promise for the generation of cartilage, by engineering tissue constructs loaded with seed cells in vitro for subsequent implantation in vivo. However, concerns associated with donor site morbidity, cell dedifferentiation, and the limited life span of the cell source have restricted the forefront of such applications. In this study, injectable hydrogels based on poly(N-isopropylacrylamide) (PNIPAAm) and chondroitin sulfate (ChS) will be developed, with the ultimate aim of synthesizing injectable, biocompatible and biodegradable hydrogels with improved mechanical strength for cartilage tissue engineering applications without seed cells implantation. The major limitation for PNIPAAm used in tissue engineering applications is that it is nonbiodegradable and not readily cleared away from the body under physiological conditions. Living radical polymerization will be employed to synthesize PNIPAAm with controlled molecular weight to be degraded and excreted from the body. In addition, click chemistry will be used to synthesize hydrogels with a well-defined structure and well-controlled properties, such as degradation rate and mechanical strength. The study will provide a novel system for the cartilage repair and promote the development of tissue engineering.

组织工程技术已成为关节软骨缺损修复的研究热点。传统的组织工程修复为体外培养足够的种子细胞，种植于生物材料上，构建细胞/支架复合物，进而植入体内修复软骨缺损。然而由于种子细胞来源有限，培养条件苛刻，且种植于生物材料上会部分或完全丧失生物活性，限制了其在临床应用中的普遍推广。本项目旨在设计合成一系列软骨组织工程支架，在不植入种子细胞的情况下，于体内诱生出具有修复功能的软骨细胞。基于这一思路，本项目设计了以聚N-异丙基丙烯酰胺(PNIPAAm)和硫酸软骨素(ChS)为基质的温敏型可注射水凝胶体系。然而由于PNIPAAm不可生物降解，在一定程度上限制了其作为支架材料的应用。本项目拟通过活性自由基聚合合成可生物降解的PNIPAAm基聚合物，通过点击化学精确控制引入的ChS的量，从而得到具有生物降解性及较好机械强度的可注射水凝胶体系，考察其对关节软骨缺损的修复效果，为关节软骨缺损修复提供新的思路。

利用支架促进骨修复是目前组织工程领域普遍采用的有效方法，然而，现有的支架存在操作复杂、创伤大、不易降解等缺陷。本项目旨在发展一种可生物降解的可注射水凝胶，探讨其作为骨修复支架的可行性。为此，我们利用活性可控自由基聚合合成了一系列聚N-异丙基丙烯酰胺(PNIPAAm)基聚合物，利用点击化学将生物大分子硫酸软骨素与聚合物骨架结合，制备了一系列可生物降解的、有较好机械强度的可注射水凝胶支架材料，考察了聚合物组成及分子量对可注射水凝胶性能的影响，研究了可注射水凝胶对大鼠颅骨缺损的修复效果。研究结果表明，聚合物及可注射水凝胶的合成分别采用活性自由基聚合和点击化学，可实现反应的高效可控和高选择性。凝胶设计摒弃了交联剂的使用，利用温敏型可注射水凝胶的形成机制制备一系列水凝胶，并将可注射水凝胶作为骨缺损修复的支架材料，方法简单易行，且对大鼠颅骨缺损有较好的修复效果。本项目的实施不仅拓展了PNIPAAm基聚合物在组织工程领域的应用，而且为解决传统骨修复支架操作复杂、创伤大、不易降解等问题提供了新的思路，为研制出新型骨修复支架奠定了理论和技术基础。

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