Solvent-responsive strong hydrogel with programmable deformation and reversible shape memory for load-carrying soft robot

Abstract

The development of shape deformation hydrogels has aroused interests of their immense applications in diverse fields such as actuators, soft robotics, and artificial muscles. However, the existing deformable hydrogels can hardly meet the requirements of facile preparation, excellent mechanical properties and reversible shape memory, which greatly limits their further applications. In this work, a new type of fully physically cross-linked deformable hydrogel with mechanically strong, tough, stretchable, and solvent-responsive property is fabricated via free radical polymerization at room temperature, followed by immersed in a Fe3+ aqueous solution. The strong physical interactions of polyacrylic acid (PAA)-Fe3+ metal complexation and hydrogen bond endowed this hydrogel with high tensile strength (~5.14 MPa), high stretchability (~1000%), high toughness (~20.36 MJ/m3) and excellent flexibility (~0.53 MPa). In addition, programmable shape deformation hydrogel is achieved by selective coating of Fe3+ on surface, the hydrogel strips can be deformed into arbitrary shapes such as the letter “o”, “d”, “s”, and “w”. More impressively, reversible shape recovery of hydrogel has been achieved via two methods: the elimination of coated Fe3+ with the reaction of NaOH and the dehydration of the glycerin. Taking advantage of this property, we simulate the closure and opening of hydrogel flower by soaking it into water and NaOH/glycerin alternately. Moreover, the soft robotic gripper has been fabricated based on the mechanically strong and solvent-triggered hydrogel, capable of grabbing about 1.56 times its own weight, which indicating the potential application as load-carrying soft robots.