Electrically controlled underwater object manipulation with adhesive borate ester hydrogels

Underwater (especially under seawater) object manipulation is a highly desirable skill for automated or intelligent robots, yet it remains a daunting challenge. We show that simply pasting a piece of electrically controlled reversible adhesive borate ester hydrogel onto the robotic arm achieves underwater object manipulation capability. The hydrogels show high adaptability in underwater environments due to the coupling of rigid and flexible borate ester crosslinks. Under the electrical stimulation (voltage ≤15 V, duration ≤30 s), the hydrogels generate maximum adhesion strengths of about 52.2, 23.6, 35.2, and 32.5 kPa on a copper surface in air, freshwater, artificial seawater, and natural seawater, respectively. Simply reversing the electric field direction makes the hydrogels almost nonadhesive. A robotic manipulator assembled with the hydrogels can lift, carry, and release objects both in air and underwater environments. These electrically responsive adhesive hydrogels may provide an alternative route for the design of robotic manipulators.