Hydrogel-actuated Soft Sucker with Mucus Secretion

Suction is a nature-inspired adhesion strategy which has been successfully applied in industry for decades. Their high adhesive force and energy efficiency make suckers light weight and low cost. However, the requirement for compact grippers conflicts with the bulky and heavy vacuum pumps used in existing suckers. This work proposes a novel hydrogel-actuated soft sucker inspired by the octopus sucker to realise compact, compliant and adaptive suction which needs no external vacuum supply. The sucker is actuated through volume change within a double-network, thermo-sensitive hydrogel. When the hydrogel is heated, its molecular structure collapses, generating a suction force and simultaneously secreting water around the sucker rim to strengthen the suction. When the hydrogel is cooled, it reabsorbs water, recovering its initial shape and eliminating the suction force. On a dry on-land surface, the proposed sucker is capable of adhering to rough surfaces by utilizing water secretion, similar to the mucus secretion of octopus suckers. Underwater, the sucker further exhibits reversible attachment and detachment capability. Simulation results and experimental results demonstrate the practicality of this suction strategy. By applying a current of 0.3 A to generate joule heat, pressure differentials of -4.54 kPa and -4.02 kPa with respect to atmospheric pressure can be generated underwater and on land, respectively. We believe this hydrogel-actuated soft sucker is a significant new technology for next-generation safe, compliant and compact robotic suckers.