A natural amphoteric polyelectrolyte hydrogel film was prepared by solution blending of soybean protein (SPI) and carboxymethylchitosan (CMCS), and cross-linked with epichlorohydrin. Under electric stimulus such a hydrogel quickly bends toward one electrode, showing an electrical sensitive behavior. Because of its amphoteric nature, the hydrogel bends either toward the anode (pH＜6) or cathode (pH＞6), depending on the pH of the electrolyte solution. Besides pH value, other factors, such as electric field strength and thickness of the hydrogel also influence the electromechanical behavior of the hydrogels. Compared with two other natural electroactive hydrogels, i.e., chitosan/carboxymethylcellulose hydrogel and chitosan/carboxymethylchitosan hydrogel reported previously, SPI/CMCS hydrogel exhibits a good electrical sensitivity either at a relative strong acidic condition (pH＝3～4) or a neutral condition (pH＝7), which widen the application area of the natural electroactive hydrogels.

Key words: protein, polysaccharide, amphoteric, smart hydrogel