Nature-inspired strategies for the synthesis of hydrogel actuators and their applications

Nature endows numerous organisms with the ability to realize their basic physiological activities through stimulus-responsive actuation. Inspired by these interesting biological structures, various biomimetic hydrogel actuators with excellent controllability, fast response, and toughness have been developed. Here, the principles of enabling stimulus-responsive behavior in polymer materials are first reviewed for the example of biological materials and subsequently recent progress in implementing stimuli-response behavior in bioinspired hydrogel actuators are being discussed. Particular emphasis is on the mechanisms underlying mechanical toughening of hydrogel actuators and its role in applications. The goal is to highlight recent progress, find the common threads, and discuss the fundamental differences to determine the current challenges and future directions for this field.