The Research Of Supramolecular Shape Memory Hydrogel Based On Dynamic Covalent Bond

As a soft matter with stimulating responsiveness,shape memory hydrogels have attracted many researchers'attention due to their softness,toughness,high water content and excellent biocompatibility.However,conventional hydrogels are crosslinked into three dimensional networks by chemical crosslinkers,which hinders their plastic deformation process.More importantly,the function and applications of shape memory materials are dramatically restricted by the number and complexity of memory shapes.Therefore,it is significant to develop a plastic shape memory hydrogel to realize the rebuilding and recycling of the gel.Hydrogels constructed by supramolecular interactions or dynamic chemical bonds can adjust their intermolecular interactions by external stimuli at room temperature.Thus,plastic deformation and shape memory process can be realized via the reversible destruction of cross-linking points.In other words,shape memory hydrogels based on supramolecular action or dynamic covalent bonds can achieve plastic deformation and shape memory process simultaneously.The methods of constructing Supramolecular Shape Memory Hydrogels?SSMHs?with multiple stimuli responsiveness have gradually developed in the collective efforts of scholars at home and abroad.However,the mechanical properties of these gels are generally poor and their shape memory ratios and stability are relatively low,which keep them far from the actual application.Therefore,it is still a great challenge to develop a SSMH with faster shape memory and recovery ratios and excellent mechanical properties.This thesis has done the following work on the construction and application of SSMHs based on dynamic covalent bonds:1.PAAm/PVA hydrogels with semi-interpenetrating network structure were obtained through heat-induced polymerization of the mixture of acrylamide?AAm?,bisacrylamide?Bis?and polyvinyl alcohol?PVA?.Fast shape memory process of the gel can be achieved in borax solution and shape recovery process can be realized in acid/glucose solution on the benefit of the small molecule-induced extremely simple shape memory strategy.These shape memory/recovery process can be continuously adjusted between minutes and tens of minutes.What's more,this method not only plays an important role in shape memory,but also is a good strategy for constructing tough hydrogels.The dynamic boronic ester bond network with the ability to dissipate huge energy is introduced into the chemically cross-linked polyacrylamide network,which effectively realizes the transformation of the single network gel with poor mechanical properties to the tough dual-network gel.2.Pure PVA hydrogels were prepared by freezing-thawing cycle method,and the gel can be remolded into arbitrary shape at 60°C.By controlling the number of freezing-thawing cycle and programming time of shape memory,fast and efficient shape memory processes of the gel in borax solution and rapid shape recovery processes in acidic or fructose solutions were achieved.These shape memory/recovery processes can be efficiently controlled within minutes,which have significant improvements over PAAm/PVA gels.The PVA hydrogels can complete the transition from single crosslinked single network structure to double crosslinked single network structure via soaking the sodium tetraborate solution.In addition,the method is also a good strategy for constructing a tough physically crosslinked hydrogel.There are two kinds of physical crosslinks in PVA networks.This structure can effectively dissipate a large amount of energy.3.The fluorescence PVA hydrogels were obtained via incorporating perylene tetracarboxylic acid grafted gelatin into the PVA hydrogel system by physical blending method and their shape memory behavior and fluorescence emission properties were explored.Based on the mechanism of photoinduced electron transfer,selectively quenching fluorescence was achieved by ionoprinting with filter paper adsorbed with Fe³⁺,which realized the loading of the pattern and text information and information encryption on the gel.In order to further improve the confidentiality of information,shape memory function and information load capacity of the gel were combined to develop a fluorescent shape memory hydrogel anti-counterfeit label with helix structure.