Clear hydrogel robots that can quickly move and exert measurable force were inspired by glass eels, "tiny, transparent, hydrogel-like eel larvae that hatch in the ocean and eventually migrate to their natural river habitats."
Via MIT News:
The robots are made entirely of hydrogel — a tough, rubbery, nearly transparent material that's composed mostly of water. Each robot is an assemblage of hollow, precisely designed hydrogel structures, connected to rubbery tubes. When the researchers pump water into the hydrogel robots, the structures quickly inflate in orientations that enable the bots to curl up or stretch out. The team fashioned several hydrogel robots, including a finlike structure that flaps back and forth, an articulated appendage that makes kicking motions, and a soft, hand-shaped robot that can squeeze and relax.