Thermo-hardening hydrogel actuators as self-locking grippers

Soft grippers based on hydrogel actuators have aroused considerable attention due to their stimuli-responsive grasping and releasing capacity. However, it remains a significant challenge for hydrogel grippers to achieve robust grasping. Herein, we present a bilayer hydrogel gripper with a microgel-containing poly(N-isopropylacrylamide) (PNIPAm) hydrogel layer as the actuating layer and a poly(acrylic acid)-calcium acetate (PAA-Ca(CH₃COO)₂) hydrogel layer as the thermo-hardening layer. The soft gripper can perform the grabbing action owing to the contraction of the PNIPAm composite layer. Subsequently, the grab action can be locked by enhancing the stiffness of the PAA-Ca(CH₃COO)₂ layer, and the hydrogel gripper can lift up to 500 times its own weight. Moreover, the soft gripper is capable of working in various grasp modes, demonstrating its robustness in versatile tasks. The presented strategy is expected to open a new avenue for enhancing the grasp force of soft actuators.