Bioinspired hydrogel jellyfish with mechanical flexibility and acoustic transparency

The uniqueness of soft materials such as hydrogels allows for great potential for new soft robots and actuators. Conventional underwater robots are generally crafted of rigid structures and materials with water-mismatched acoustic impedance, severely limiting their underwater operating capabilities. Therefore, flexible and acoustically transparent soft robots show great prospects for applications in marine exploration, biomedical engineering, etc. Inspired by the high water content of jellyfish, we report a hydraulically actuated bioinspired hydrogel jellyfish. The acoustic backscattered energy of the hydrogel jellyfish is reduced to about 1/270 compared with conventional underwater robots, achieving omnidirectional transparency under broadband acoustic detection from 10 kHz to 1 MHz. Moreover, the body length of hydrogel jellyfish can contract to about 1/3 of its original length under hydraulic control, exhibiting flexible motion to pass through narrow orifices. This design can potentially establish generic design principles for constructing next-generation mechanically flexible and acoustically transparent robots.