Actuators assembled from hydrogel blocks of various shapes via condensation reactions

Hydrogel-based actuators have attracted much attention and shown promising applications in many fields. However, it remains a challenge to assemble two hydrogel sheets into a double-layer actuator due to their slippery and non-adhesive nature. Herein, we present a simple and reliable strategy that allows two hydrogel sheets to be bonded together well with chemical bonds formed in condensation reactions, only requiring interfacial contact and then heat-treatment. The results shown that the condensation reactions can occur under heat-treatment and that the two hydrogel layers have good interfacial bonding. The double-layer strip hydrogels prepared in this method showed different deformation rate and bending extent, which can be well tuned by changing internal structures and external stimuli. Complex and controllable three-dimensional shapes of the assembled blocks can be obtained through well-tailored structures. A four-arm gripper prepared in this approach can implement the grasping and releasing an object quickly with different stimuli. This work provides a facile approach in achieving hydrogel bonding and preparing intelligent double-layer soft actuators.