Xenobots, named after the African clawed frog (Xenopus laevis), are synthetic lifeforms that are automatically designed by computers to perform some desired function and built by combining together different biological tissues. Whether or not xenobots are robots, organisms, or something else entirely remains a subject of debate among scientists, with one of the researchers saying: "They're neither a traditional robot nor a known species of animal. It's a new class of artifact: a living, programmable organism."

Xenobots are less than a 1 millimeter (0.039 inches) wide and composed of just two things:

skin cells and heart muscle cells, both of which are derived from stem cells harvested from early (blastula stage) frog embryos.

The skin cells provide rigid support and the heart cells act as small motors, contracting and expanding in volume to propel the xenobot forward.

The shape of a xenobot's body, and its distribution of skin and heart cells, are automatically designed in simulation to perform a specific task, using a process of trial and error (an evolutionary algorithm).

Xenobots have been designed to walk, swim, push pellets, carry payloads, and work together in a swarm to aggregate debris scattered along the surface of their dish into neat piles.

They can survive for weeks without food and heal themselves after lacerations.

Other kinds of motors and sensors have been incorporated into xenobots.

Instead of heart muscle, xenobots can grow patches of cilia and use them as small oars for swimming.

However, cilia-driven xenobot locomotion is currently less controllable than cardiac-driven xenobot locomotion.

An RNA molecule can also be introduced to xenobots to give them molecular memory: if exposed to specific kind of light during behavior, they will glow a prespecified color when viewed under a fluorescent microscope.

 

Note:   The above text is excerpted from the Wikipedia article Xenobot, which has been released under the GNU Free Documentation License.