A jelly-like artificial muscle for an untethered underwater robot

Underwater robots desire versatile, water-adaptive, untethered, and rapidly actuating soft artificial muscles. Existing artificial muscles compromise between high water compatibility and untethered rapid actuation. Taking inspiration from the watery and fast contraction characteristics of jellyfish, we present a jelly-like muscle design that features an extremely soft (elastic modulus, 66.9 kPa) and watery (water content, 83.3%) structure. The jelly-like muscle can instantly respond to electrical stimuli and provide underwater propulsion. The muscle can shift propulsion direction by simply tuning the voltage signal and quickly recover from electromechanical failures through repair. An untethered robot can be assembled by stimulating the muscle with an onboard power system. The robot reaches a maximum speed of 0.91 cm/s (0.3 body length per second) and has an endurance of 15.7 min with a 500-mAh lithium-ion battery. Robots can be constructed in different forms by tailoring the jelly-like muscle, which is promising for various applications.