(CNN) Scientists have created the world's first living, self-healing robots using stem cells from frogs.

Named xenobots after the African clawed frog (Xenopus laevis) from which they take their stem cells, the machines are less than a millimeter (0.04 inches) wide -- small enough to travel inside human bodies. They can walk and swim, survive for weeks without food, and work together in groups.

These are "entirely new life-forms," said the University of Vermont, which conducted the research with Tufts University's Allen Discovery Center.

Stem cells are unspecialized cells that have the ability to develop into different cell types. The researchers scraped living stem cells from frog embryos, and left them to incubate. Then, the cells were cut and reshaped into specific "body forms" designed by a supercomputer -- forms "never seen in nature," according to a news release from the University of Vermont.

A xenobot with large hind limbs and smaller forelimbs, layered with red heart muscle.

The cells then began to work on their own -- skin cells bonded to form structure, while pulsing heart muscle cells allowed the robot to move on its own. Xenobots even have self-healing capabilities; when the scientists sliced into one robot, it healed by itself and kept moving.

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