Engineers have fabricated transparent gel-based robots that move when water is pumped in and out of them and can perform tasks like grabbing and releasing a live fish or kicking a ball under water.

According to the results — published in the journal Nature Communications — these robots can also perform fast and forceful tasks like kicking a ball underwater.

The robots are made entirely of hydrogel — a tough, rubbery, nearly transparent material that's composed mostly of water. 

"Hydrogels are soft, wet, biocompatible and can form more friendly interfaces with human organs," said Xuanhe Zhao, associate professor at Massachusetts Institute of Technology.

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.

Since the robots are powered by and made almost entirely of water, they have similar visual and acoustic properties to water. 

The researchers propose that these robots, if designed for underwater applications, may be virtually invisible.

"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," Zhao added.