MIT engineers have fabricated transparent gel robots that can grab and release live fish. The robots are made entirely of hydrogel - a rubbery material that’s composed mostly of water. Each robot is made up of hollow, precisely designed hydrogel structures, connected to rubbery tubes. When the researchers pump water into the 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. If designed for underwater applications, the robots may be virtually invisible.