Researchers at MIT have developed gel-based robots that are so at home in the water that you can barely see them when they're submerged.

Made from hydrogel — which as the name implies, is mostly just water — the scientists created a flapping fin robot, a kicking appendage robot and a grabbing claw robot that is featured in the video above. Each robot is powered by water pumped in and out of its structures, and that water is what allows the robots to move, kick or grasp. Similar hydrogel robots have absorbed water slowly, but that process makes those robots slow moving, and they perform their actions with less force than these water-pump-powered robots do.

Researchers are pleased with how fish responded to the soft robots. "When you release the fish, it's quite happy because [the robot] is soft and doesn't damage the fish. Imagine a hard robotic hand would probably squash the fish," lead researcher Xuanhe Zhao, an associate professor of mechanical engineering and civil and environmental engineering at MIT, explained in a press release.

While the robot would clearly make any angler's day, Zhao and his team are eyeing medical applications for their hydrogel robots.

"Hydrogels are soft, wet, biocompatible, and can form more friendly interfaces with human organs," Zhao says. "We are actively collaborating with medical groups to translate this system into soft manipulators such as hydrogel 'hands,' which could potentially apply more gentle manipulations to tissues and organs in surgical operations."

See-through robot is a fisherman's dream
The hydrogel robot is flexible but strong, and it's entirely powered by water.