Now a team of scientists has repurposed living cells — scraped from frog embryos — and assembled them into entirely new life-forms. These millimeter-wide “xenobots” can move toward a target, perhaps pick up a payload (like medicine that needs to be carried to a specific place inside a patient) — and heal themselves after being cut. “These are novel living machines,” says Joshua Bongard, a computer scientist and robotics expert at the University of Vermont who co-led the new research. “They’re neither a traditional robot nor a known species of animal. It’s a new class of artifact: a living, programmable organism.” Roboticists tend to favour metal and plastic for their strength and durability, but Levin and his colleagues see benefits in making robots from biological tissues. When damaged, living robots can heal their wounds, and once their task is done they fall apart, just as natural organisms decay when they die. The biological robots have an advantage over their much larger metal or plastic brethren — they leave no trace behind. “These xenobots are fully biodegradable,” Bongard said in the statement. “When they’re done with their job after seven days, they’re just dead skin cells.” “These are very small, but ultimately the plan is to make them to scale,” co-author Michael Levin, the director of the Allen Discovery Center at Tufts University, told The Guardian. “You look at the cells we’ve been building our xenobots with, and, genomically, they’re frogs. It’s 100 percent frog DNA – but these are not frogs. Then you ask, well, what else are these cells capable of building?” said biologist Michael Levin of Tufts University. “As we’ve shown, these frog cells can be coaxed to make interesting living forms that are completely different from what their default anatomy would be.” Although the team calls them ‘living’, that may well depend on how you define living creatures. These xenobots are not able to evolve on their own, there are no reproductive organs, and they are unable to multiply. When the cells run out of nutrients, the xenobots simply become a small clump of dead cells. (This also means they are biodegradable, which gives them another advantage over metal and plastic robots.) Although the current state of the xenobots is relatively harmless, there is the potential for future work to incorporate nervous system cells, or develop them into bioweapons. As this field of research grows, regulation and ethics guidelines will need to be written, applied and adhered to. But there is plenty of potential good, too. “We can imagine many useful applications of these living robots that other machines can’t do,” Levin said, “like searching out nasty compounds or radioactive contamination, gathering microplastic in the oceans, travelling in arteries to scrape out plaque.” While the frog-bots are still at a very early stage in development, it’s possible that more complex versions could be used in the future for tasks like nano-surgery (performing jobs such as cleaning plaque from arteries or delivering drugs) and cleaning up micro-plastics.