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.

"These are novel living machines," said Joshua Bongard, one of the lead researchers at the University of Vermont, in the news release. "They're neither a traditional robot nor a known species of animal. Xenobots don't look like traditional robots -- they have no shiny gears or robotic arms. Instead, they look more like a tiny blob of moving pink flesh. The researchers say this is deliberate -- this "biological machine" can achieve things typical robots of steel and plastic cannot. Some xenobots had holes in their center -- which could potentially be used to transport drugs or medicines.