An iodine-driven muscle-mimicking self-resetting bilayer hydrogel actuator

Hydrogels that can swell and deswell under the influence of opposing external stimuli have frequently been reported as muscle-mimicking materials. However, the mechanism of such materials is markedly dissimilar to that of natural muscles. Natural muscles contract when fueled by ATP and spontaneously relax once ATP is completely consumed. The subtlety of this "self-resetting" mechanism is avoiding the equivalent opposite modulation to reset the size and shape of the muscle, which may easily result in the cumulation of action error after several repeating cycles. In this article, we fabricate a bilayer hydrogel actuator with the aid of the I₂-responsiveness of poly(ethylene glycol)-based hydrogel. When this actuator is coupled with a reaction network containing NaIO₃, NaI, and CS(NH₂)₂, which generates I₂ as an intermediate product, it will temporarily deform and recover spontaneously with the consumption of I₂. Such an actuator is highly similar to natural muscles in terms of the actuation mechanism. Several biomimicking functions were achieved by this actuator.