Salt-Responsive Polyampholyte-based Hydrogel Actuators with Gradient Porous Structure

Stimuli-responsive materials with shape deformation properties play an important role in many fields such as artificial muscles, soft robots, and tissue engineering. Among them, stimuli-responsive hydrogels as actuators possessing shape deformation properties have been focused on. In this paper, a polyampholyte-based hydrogel with gradient pore construction is synthesized by a facile one-step random copolymerization, in which two sides of the reaction mold possess different hydrophilicity and hydrophobicity. The micro-Fourier transform infrared spectra prove the gradient distribution of chemical composition. Owing to the gradient pore construction and the ionic bonds, the polyampholyte-based hydrogel can rapidly change the shape when exposed to the environmental-friendly stimulus of water and recover to the original shape in salt solution, and the maximum bending angle reaches about 180°. Besides, this hydrogel actuator has a shorter recovery time compared with response time and the response/recovery time ratio is 2. By adjusting chemical and non-chemical factors including physical cross-link content, aspect ratio, salt solution concentration and soaking time, shape deformation degree and response/recovery time are controllable. Gradient pore construction and locomotion make this hydrogel actuator become a potential material for multiple applications.