Early last year, a team of researchers announced the world's first living machines—bundles of stem cells from African clawed frogs (Xenopus laevis) that could be programmed to accomplish certain tasks. The sand grain–sized cells could successfully move microscopic objects, whiz around Petri dishes and even self-heal, Katherine J. Wu reported for Smithsonian last year.
"Most people think of robots as made of metals and ceramics but it's not so much what a robot is made from but what it does, which is act on its own on behalf of people," co-author Josh Bongard, a computer scientist at the University of Vermont, tells Katie Hunt for CNN. "In that way it's a robot, but it's also clearly an organism made from genetically unmodified frog cell."
Since their original study, the team has been working to harness the power of these tiny robots—named "xenobots" after the clawed frogs' genus Xenopus. In a new development, the team announced that xenobots can now reproduce in a way that is completely different from any plant or animal known to science: by scooping up free-floating cells and assembling them into new clusters, Nicola Davis reports for the Guardian. The team published their findings this week in the journal Proceedings of the National Academy of Sciences.
"Frogs have a way of reproducing that they normally use but when you ... liberate (the cells) from the rest of the embryo and you give them a chance to figure out how to be in a new environment, not only do they figure out a new way to move, but they also figure out apparently a new way to reproduce," co-author Michael Levin, a biologist at Tufts University, tells CNN.
To create the xenobots in the first place, the team used a supercomputer to create a blueprint for a new life form. With the design in hand, they collected stem cells from the frogs' embryos and incubated them before reconfiguring them Frankenstein-style using tiny tweezers and an electrode into the shape designed by the supercomputer. The xenobots could then be programmed to complete certain tasks, and they've grown more complex since then, according to a press release.
In about five days, xenobots can form spheres of around 3,000 cells when they cluster. Since they're able to work together, the robo-blob can move around and push single cells together to form new xenobots, Carissa Wong reports for New Scientist.
It's a process called kinematic self-replication, a process only observed in molecules and not living things, Tom McKay reports for Gizmodo.
"One [xenobot] parent can begin a pile and then, by chance, a second parent can push more cells into that pile, and so on, generating the child," co-author Josh Bongard, an expert in evolutionary robotics at the University of Vermont, tells New Scientist.
But there's a limit to how many baby bots can be created. "It turns out that these xenobots will replicate once, one generation, they will make children. But the children are too small and weak to make grandchildren," Bongard tells the Guardian.
Plus, the xenobots could only reproduce under specific conditions. To make them more effective, the team used artificial intelligence to test billions of different body shapes and configurations on a supercomputer. Instead of a sphere, it found that a Pac-Man-like, C-shaped bot was the best at gathering individual stem cells in its mouth and bundling them into new baby bots, CNN reports.
"The AI didn't program these machines in the way we usually think about writing code. It shaped and sculpted and came up with this Pac-Man shape," Bongard tells CNN. "The shape is, in essence, the program. The shape influences how the xenobots behave to amplify this incredibly surprising process."
Though this research is in its infant phases, the team has high hopes for the xenobots. With further development, they could be used in medicine—such as to help deliver drugs within the body—or to clean up environmental contaminants, Smithsonian reported last year.
"There's all of this innate creativity in life," Bongard says in the press release. "We want to understand that more deeply—and how we can direct and push it toward new forms."