化学交联双网络纳米增强可降解仿生水凝胶及其促骨再生机理研究

Hydrogels are potential implants used for bone tissue engineering due to their structural similarity to extracellular matrix (ECM). However, the current synthesized hydrogels can’t meet the requirement from clinical settings. This project aims to develop a biodegradable, biomimetic, nano-reinforced double network hydrogel by chemical crosslinking for bone regeneration..Firstly, gelatin methacrylate（GelMA） is synthesized by adding methacrylate groups to the amine-containing side-groups of gelatin, which becomes photocrosslinkable. Secondly, methacrylated heparin (MAHep) were covalently coupled to the heparin main chains by reacting the carboxylic acid reactive groups of the heparin with the amines of the 2-aminoethyl methacrylate (AEMA) by carbodiimide chemistry. Thirdly, TiO2 nanoparticles were functionalized with atom transfer radical polymerization (ATRP)-initiating group (DA-BiBB) by the oxidative copolymerization of dopamine (DA) and ATRP-initiator modified-DA. Finally, the hydrogel is obtained through free-radical polymerization by exposing the GelMA, MAHep and DA-BiBB functionalized TiO2 to UV light. A high-density of covalent cross-linking sites on the surfaces of DA-BiBB functionalized TiO2 nanoparticles were initiated to GelMA and MAHep polymer via surface-initiated ATRP (SI-ATRP) method, which extremely reinforced the biodegradable GelMA/MAHep hydrogel. Then the surfaces of the composite hydrogel were modified with BMP-2 and VEGF for constructing a biomimetic microenvironment of natural ECM on the surfaces of implants, which further improved osteointegration and osteoinductivity of double network-reinforced hydrogel..This project will obtain synthetic routes of the double network hydrogel by chemical crosslinking with high toughnessl for the repair of bone defects, and uncover the mechanisms between the mechanical properties of hydrogel and double network hydrogel by chemical crosslinking . The interaction mechanisms between hydrogel intrinsic properties and cell/tissue will also be explored. The data from this project will provide fundamental principles for the design of next generation of hydrogel to treat bone defects as a single unit. The project will also be useful in the guidance for the development of biomedical engineering products in clinical applications.

水凝胶是目前骨组织修复常用的植入材料。但水凝胶存在力学性能差、不易降解、骨诱导性较差等问题，研究一种可降解的高强、仿生水凝胶材料是解决这一问题的关键。本项目拟采用表面引发自由基聚合技术，在可降解水凝胶中引入化学交联双网络结构，结合生长因子的高效固载和时序控释，合成具有高力学性能、较强骨诱导活性的可降解复合水凝胶。该水凝胶以改性明胶和肝素两种高分子为主要成分，并在基体中引入表面功能化的TiO2纳米颗粒，紫外作用下引发TiO2纳米颗粒、明胶、肝素间相互交联，形成纳米化学交联、高分子交联增强的可降解水凝胶。随后对水凝胶进表面仿生功能化，修饰骨诱导因子BMP-2和血管化因子VEGF，进而构建表面仿生微环境的的高强度可降解水凝胶，实现对骨缺损的快速有效修复。揭示水凝胶化学交联双网络与力学性能的关系, 阐明水凝胶物理化学性能与细胞/组织的相互作用机理。预期成果为临床骨修复材料的研发奠定基础。

组织工程水凝胶因其机械性能、化学组分和生物信号可以动态调控继而能在多尺度上模拟细胞外基质（ECM）微环境而受到医学研究者的广泛关注。特别是仿生组织工程支架的出现为组织修复提供了的有效的解决方法。然而，现有仿生支架在物化结构、降解性能、力学强度和生物活性方面很难同时满足骨组织修复要求。针对这些问题，我们通过组合筛选方法和纳米无机材料添加成功获得力学性能、生物活性和降解性能可调控的纳米复合高强水凝胶。 我们研究发现聚丙烯酰胺/双键化海藻酸钠/无机二维黑磷纳米复合水凝胶具有优越的力学性能和生物活性。值得注意的是，二维无机纳米黑磷材料可以在体外诱导CaP晶体颗粒形成，利用黑磷材料固有性质可以提高水凝胶的矿化能力。最后，体外和体内数据证明了植入材料内部复合的纳米黑磷材料、随后诱导CaP纳米颗粒结合其优异的机械性能（高刚性和超韧性）能为细胞和组织再生提供有利的ECM微环境，从而诱导细胞向成骨分化、提高复合材料骨组织再生的能力。在此基础上，我们还成功制备了可在湿润环境下对组织具有一定粘附强度的仿生植入材料， 该水下粘附材料结合水凝胶的表面修饰有望为水凝胶的湿润粘附带来新的解决方案，从而为骨组织缺损稳定修复提供灵感和思路。

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