Inspired by natural creatures, soft robots possess the unique advantages of large actuation and excellent adaptability. Untethered designs of soft robots are drawing more attention to researchers, but current research is limited. Also, there is an increasing need to improve the performance of bio-mimetic robots. This work describes an untethered soft robotic jellyfish with high mobility that can mimic a natural jellyfish’s performance. The electrode of the robotic jellyfish is made by sandwiching carbon grease between two layers of dielectric elastomer film. The frame of the material, where six plastic paddles are attached, is made from a silicone elastomer. The robotic jellyfish has a maximum recorded swim speed of up to 1 cm s−1, with a peak thrust force of 0.000 12 N. A finite element simulation is developed to study the performance of the robotic jellyfish in a theoretical manner. By embedding a compact remote-controlled power source, the robotic jellyfish is made autonomous. In this case, the max peak speed is around 0.5 cm s−1. Ultimately, the working principles of the bio-mimetic robotic jellyfish can be useful in field studies and to guide the design of soft robots and flexible devices.

Soft pneumatic actuators possess attributes of large deformation, high driving force and light weight in the application of soft robots and smart devices. However, most reported soft pneumatic actuators are with rigid hydraulic source such as motor driven pump, piston and pressurized reservoir. These rigid and heavy hydraulic sources limit the actuation and compliance of the soft robots. Inspired by the bladders and hydrostatic skeleton of natural creatures, we propose a soft hydraulic robot consisting of dielectric elastomer (DE) and hydrogel, exhibiting an excellent actuating performance. An inflated DE balloon functions as the soft hydraulic source, in which the pressure of the containing water can be tuned by voltage. Hydrogel chambers are connected to the DE balloon as the hydraulic actuator, deforming as a soft robotic gripper. A new analytical approach is proposed to describe the system’s behaviors, which couples the electromechanical actuation of DE and the hydraulic deformation of hydrogel chamber. The proposed model is validated by good agreement between the numerical and experimental data. The proposed model could serve as a new tool for modeling and characterizing soft robots with hydraulic actuation. The working principles can guide the design and control of soft robots and smart structures.