Scientists have created a new form of "robot," not made out of metal, plastic, and wiring but formed entirely out of living cells.

Reporting in the journal PNAS, researchers from the University of Vermont and Tufts University describe how they crafted the first-ever “living machines" out of cells taken from the embryos of frogs. Dubbed “xenobots,” these miniature monsters were designed using algorithms that mimic the forces of natural selection.

"These are novel living machines. They're neither a traditional robot nor a known species of animal. It's a new class of artifact: a living, programmable organism," co-lead author Joshua Bongard, a computer scientist and robotics expert at the University of Vermont, said in a statement.

"You look at the cells we've been building our xenobots with, and, genomically, they're frogs," added co-leader Michael Levin, who directs the Center for Regenerative and Developmental Biology at Tufts. "It's 100 percent frog DNA – but these are not frogs. Then you ask, well, what else are these cells capable of building?"

The new "lifeforms" might be smaller than a pinhead for now (they're around 650-750 microns in diameter), but they’re already capable of performing specialized jobs. One of the living machines is able to propel itself through water using two limbs, while another has a pocket that could be used to carry some very tiny cargo. Using these skills, they could be used to deliver medicine in patients’ bodies or clean up pollution from the sea.

A simulate organism (left) and an actual xenobot (right) built entirely from frog skin (green) and heart muscle (red) cells. Sam Kriegman, UVM

Squishy “living” machines hold many advantages over their rigid counterparts. As nature shows, living systems are notably more robust than any technology developed so far. For example, in theory, the xenobots could be developed to regenerate themselves and heal when damaged. They are also completely biodegradable.

For this project, the team started by developing an “evolutionary algorithm,” which simulates the process of natural selection to guide the xenobots' design. They assigned a task, such as movement in one direction, and then let the computer virtually assemble the simulated cells in different forms, over and over again, until one performed the skill. Inspired by the design crafted by the AI, the team assembled the xenobots using the skin and heart muscle cells of an African clawed frog (Xenopus laevis).

The research has a couple of implications: along with the potential practical uses, the creation of these little guys could be used to help "crack the code" of life.

"The big question in biology is to understand the algorithms that determine form and function," added Levin. "The genome encodes proteins, but transformative applications await our discovery of how that hardware enables cells to cooperate toward making functional anatomies under very different conditions."