光驱动界面作用动态构筑梯度结构水凝胶及其力学性能的控制与测定

Gradient mechanical environment of cell culture in vitro has a significant impact on its biological behavior. Relationship between mechanical property of cell culture and cell phenotypic shift has begun to attract more attention from the researchers. It is an important link in the above observation and research to build an saving energy and high efficient synthesis technology of polymer with gradient distribution in mechanical property. On the theoretical study on the frontal photopolymerization （FPP）for long time, we use self-assembling effect which is typical nonlinear characteristic of FPP to solve this problem. The onium salt is utilized as photoacid generator to produced protonic acid and drives organic precursor into nanoparticles while under UV light. Due to the poor compatibility of ionic onium salt, some fraction of onium salt will be squeezed out from the fast-formed hydrogel network with functional nanoparticles as crosslinking agent and concentrated in the lower layer gradually. The increased concentration of acid was of course in favor of the formation of nanoparticles. Thus, it will be understood that more and more inorganic particles is produced and denser linking network is formed with the polymerization front progresses. So the mechanical property of hydrogel will changed with the spatial variations of nanoparticles concentration. An electroresistance measurement will be firstly developed to accurately follow the front traveling frontal photopolymerization for the first time to investigate spatiotemporal dynamics。The reaction characteristics、controlling factors and gel mechanism will be discussed in detail. We also systematically study spatial micro-morphology and mechanical property. It has important and practical significance for exploring the polymer with special structure and property.

胞外基质的梯度力学环境对细胞生物学行为的影响是不可忽视的，基质力学性能与细胞表型改变的相关关系已开始引起研究者关注，而研究一种节能、高效，且能使力学性能梯度分布的材料制备工艺，是开展上述观察和研究的重要环节。本项目在长期研究前线光聚合应用的基础上，提出利用前线光聚合中前线界面自排挤这一非线性特征，在前线推进同时，使光产酸剂发生向下迁移富集，光解后形成酸值的轴向梯度分布，加速下层纳米前驱体的转化，促使功能化纳米粒子原位生成，并梯度分散于凝胶网络中，功能化纳米粒子即作为填充剂又作为交联剂参与单体聚合，在聚合物体系中形成交联密度梯度分布的聚合物网络。并首次采用电阻法实时监测前线光聚合时空动力学过程，对前线光聚合制备梯度水凝胶的反应特征、控制因素、凝胶机理进行理论上的深刻揭示，对产物的梯度微观形貌及力学性能进行了详细表征，这对于探索合成具有特殊结构和性能的材料具有重要的实际工作意义。

本项目利用前线光聚合的中前线的自排挤现象，在前线推进的同时，原位生成纳米粒子，自发在体系中形成浓度空间梯度分布，并稳定分散于同步形成的水凝胶网络中，构筑了力学强度梯度分布的杂化水凝胶。推导了光引发剂浓度，光强，初级自由基的产生速率等的时空方程；通过实验检测了前线推进过程中温度分布、分计量及分子量分布、残余引发剂浓度，发现与理论方程相对应，其分布均在空间呈现梯度的特性。对前线自排挤作用的产酸效应进行了定量测定；利用硅酸乙酯及碘鎓盐产酸机能，在前线推进的同时，原位生成纳米氧化硅/聚PNIPAm杂化水凝胶材料，发现纳米氧化硅在聚合物棒内存在轴向梯度分布。切片发分层检测，发现水凝胶内部存在微观结构及力学性能的梯度分布。研究合成一种既带有叔胺结构，又带有二苯甲酮结构，兼具光引发自由基反应及敏化功能的碘鎓盐大分子引发剂，来协调原位光产酸效率与前线推进速率的协同性，与小分子引发剂相比，大分子引发剂具有较快的引发速率。为改善纳米粒子与聚合物体系的相容性，本项目联用ATRP和NRC两种手段制备表面接枝PNIPAm的纳米粒子，改善了其团聚现象，使其更好地分散在水凝胶基质中。从本项目出发，衍生出剃度水凝胶的前线光聚合制备技术，为多种梯度材料制备提供了有益的技术和理论支持。