Chiral design of tough spring-shaped hydrogels for smart umbrellas

Developing hydrogel artificial muscles to mimic the motion of natural muscles have long attracted scientists from the perspective of materials science for potential applications in soft robotics. However, rational design of hydrogel artificial muscles with large stroke, rapid actuation speed, and high work capacity remains a major challenge. Herein, we reported two kinds of chiral spring-shaped hydrogels that were prepared via consecutive shaping process (e.g., stretching, twisting, folding, coiling, and fixing). By switching the chirality of coil, homochiral muscle and heterochiral muscle were obtained, respectively. Homochiral muscle could rapidly expand to 560% with an average speed of 6.7 % s−1 in response to NIR irradiation, whose maximum work capacity reached 45 J kg−1. On contrary, heterochiral muscle contracted 69% within 1 min under NIR irradiation with a maximum work capacity of 33 J kg−1. Interestingly, the parasol containing homochiral muscles opened autonomously during dehydration process, while the umbrellas containing heterochiral muscle could opened rapidly when water was applied. This work provided an innovative strategy for developing tough hydrogel muscles with opposite chiralities.