Hydraulically Enhanced Electrostatic Creeping Actuator Enabled by a Liquid-Metal Fluid Electrode

Soft actuators are the core components of soft robotics. However, existing representative soft actuators, such as dielectric elastomers and hydraulically amplified self-healing electrostatic (HASEL) actuators, usually require high driving voltages (several kilovolts), limiting their practical application for human-interactive soft robotics. Here, we introduce a unique class of soft actuators, termed hydraulically enhanced electrostatic creeping (HEEC) actuators, which leverage a coupled hydraulic-electrostatic creeping mechanism to achieve excellent electro-responsive actuation under a low driving voltage. The HEEC actuator is fabricated by sandwiching a polyvinyl chloride gel (PVCG) pouch, filled with liquid metal serving as a fluid cathode, between two copper mesh anodes. In this configuration, the electric field is applied only to the dielectric PVCG membrane. The inner fluid electrode's hydraulic pressure and the PVCG's creeping adsorption simultaneously contribute to the actuation performance, allowing the HEEC actuator (achieving 19% actuation strain and 200 mN output force at 600 V) to outperform existing dielectric and hydraulic-amplified soft actuators. Furthermore, the series assembly of multiple HEEC actuators enables the design and fabrication of versatile piston actuators with tunable strokes. Finally, the application potential of the HEEC actuators is demonstrated through their successful integration into a humanoid mask (for simulating eye blinking) and a robotic arm actuation device. The HEEC actuators feature low-voltage operation and excellent deformation, making them highly promising for human-interactive soft robotics.