Underwater dielectric elastomer actuators with large bending deformation for soft robots

Soft robots are promising platforms for underwater exploration and biological sampling because of their compliance and adaptability. Dielectric elastomer actuators (DEAs), particularly bending DEAs, are appealing for underwater soft robots because they enable diverse robotic architectures. However, previously reported underwater bending DEAs still present opportunities for improvement in deformation capability, particularly in terms of deformation magnitude and actuation speed. Therefore, this paper presents an underwater DEA consisting of a layered elastomeric structure with an encapsulated water electrode and inextensible materials, which together generate unidirectional bending deformation when a high voltage is applied between the internal water electrode and the surrounding water. Consequently, the actuator achieves a maximum bending angle of 308.5° (corresponding to a curvature of 0.09/mm), which agrees well with predictions from an analytical model. Additionally, it attains an average actuation speed magnitude of 172.2°/s and a blocked force of 57.2 mN while maintaining stable actuation over 1000 cycles. The actuator was further demonstrated as an electrically driven biohybrid luminescent device incorporating Pyrocystis lunula and as a soft gripper capable of manipulating a live jellyfish. These results highlight the potential of the proposed DEA for advancing underwater soft robotic systems.