Intelligent polymer hydrogel (smart hydrogel) is a kind of intelligent material that can change volume, shape or color under the stimulation of external temperature, ionic concentration and pH. Among them, smart deformed hydrogels can transform all kinds of external energy into mechanical energy under the stimulation of the outside world, so that they can undergo reversible deformation. They will have broad application prospects in many emerging fields, such as flexible actuators, flexible sensors, soft robots, and so on. After years of development, intelligent deformed hydrogels have broken away from the single stimulus response mode and simple swelling and shrinkage behavior, and developed more complex two-dimensional and three-dimensional complex deformation. However, the traditional intelligent deformed hydrogels are usually endowed with anisotropy in the preparation of gelatin, and their deformation degree and deformation direction usually can not be changed again.
Researchers Chen Tao and Zhang Jiawei of Ningbo Institute of materials, Chinese Academy of Sciences provided feasible solutions to the above problems in the paper of "dynamic covalent polymer" album (to be published) in the 5th issue of polymer journal in 2019. Inspired by building blocks, the hydrogel is assembled and assembled like blocks. It is possible to obtain multiple anisotropic structures and multiple stimuli response capabilities from simple building blocks, thus achieving complex intelligent deformation. In this study, the phenyl boronic acid group was introduced into the hydrogel network, and polyvinyl alcohol (PVA) was used as the glue to form a dynamic borate ester bond with PVA on the surface of the hydrogel under alkaline conditions. The modular assembly of hydrogel containing benzene boronic acid group was achieved, and the adhesive strength of the hydrogel after assembly was larger than that of the bulk gel, which proved the validity of the method. Subsequently, polycation monomer acyl oxygen three ammonium chloride (METAC) and N- (NIPAm) were introduced to achieve double stimuli response of ion and temperature of double layer hydrogel. According to the design requirements, the study can be applied to any hydrogel by any glue, and successfully realized the complex reversible transformation of the hydrogel from two-dimensional to three-dimensional. Finally, the combination of two stimuli responsive hydrogels can achieve multiple stepwise driving in the same driving direction, which provides a feasible plan for the research of hydrogel soft mechanical fixture.