基于光诱导塑化的冰冻多孔水凝胶的制备与性能研究

Porous hydrogels have shown great potential for a variety of applications including waste water treatment, chromatographic separation, and tissue engineering scaffolds. Cryo-pore-forming is a fast developing technique for the preparation of porous hydrogels. The resulted products show high mechanical stability and controllable pore structure. However, this technique has a major limitation in that only water soluble non-acidic monomers can be used, which prohibits further functionalization. This proposal aims to develop a new method based on photo-induced plasticity effect. Such an effect will be introduced into nonporous hydrogels using photo reversible cross-linkers. In the frozen state, the mechanical squeezing of the ice crystals will impose microscopic stress onto the polymer chains, which can be relaxed by the photo-induced plasticity. Porous hydrogels can then be obtained after melting of the ice crystals. Since the polymerization and the pore-forming procedure are decoupled, most monomers can be used. Moreover, the pore structure can be controlled by exploring the unique spatio-temporal characteristics of the light stimulus. The proposal will investigate the underlining mechanism and the controlling parameters for the photo-induced plasticity in a microscopically stressed multi-phase polymer system.

多孔水凝胶在污水处理、色谱分离、组织工程支架等领域中有很好的应用前景。冰冻致孔技术是一种发展很快的水凝胶致孔方法。该方法操作简单，所得的多孔水凝胶机械强度较好且孔结构可控,但也存在一突出缺陷：聚合在冰冻条件下进行，适用该方法的仅有一些水溶性的非酸性单体，不利于材料的多功能化。本申请拟探索基于光诱导塑化效应制备多孔水凝胶的新方法。通过光可逆交联剂的引入合成具有光诱导塑化能力的无孔水凝胶。在冰冻状态下，水凝胶中聚合物分子链因冰晶挤压而受到微观应力作用。通过光辐照将此应力松弛，冰晶熔融后就能得到多孔水凝胶。由于聚合及致孔解耦进行，此方法可适用于大多数单体，具有很强的通用性。此外，光特有的时空可控性也可用于实现孔结构的精确调控。本申请将对光塑化冰冻致孔方法涉及的关键科学问题，即微观应力作用下多相体系中的光诱导塑化产生机理及控制规律进行系统研究。

冰模板法能够高效、可控的制备多孔水凝胶。然而，冰冻区域的不可控性以及冷冻状态对聚合反应的巨大影响，制约了多孔水凝胶制备的广度。针对冰模板法制备多孔水凝胶的原理要求与制备难点，本研究首先采用传统冰冻致孔法，包括冰冻干燥法与冰冻聚合法，细致探究凝胶体系中冰晶生长的动力学过程与最终成孔状态之间的联系，揭示冷冻干燥法得到多孔结构临时的特征，并开发了基底亲疏水性调控多孔水凝胶孔结构的方法。在充分结合上述研究内容的基础上，本研究合成含有光诱导塑化性质的水凝胶。冷冻状态下，凝胶网链将由于冰晶生长而被拉伸，此时施加紫外光照，通过引发双硫键键交换来松弛被拉伸链段。当升温冰晶融化，因为网链已经松弛而不会发生回弹，将实现水凝胶的致孔。这一致孔方式，将水凝胶的合成与致孔解耦，拓展了多孔水凝胶的制备方式。同时，采用光刻技术，本研究实现了水凝胶孔结构的空间调控，诠释了微观内应力作用下光诱导塑化的机理。