The millimeter-wide computer-designed “xenobots” – made of cells scraped from frog embryos – can move toward a target, perhaps pick up and deliver a payload (such as a medicine), and heal themselves after being cut. These “living robots,” say the researchers, promise advances in applications from in-patient intelligent drug delivery to toxic waste clean-up.
“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.”
The new creatures were designed using months of processing time on the Deep Green supercomputer cluster at UVM’s Vermont Advanced Computing Core and then assembled and tested by biologists at Tufts University (Medford, MA).
Co-leader Michael Levin, who directs the Center for Regenerative and Developmental Biology at Tufts, says, “We can imagine many useful applications of these living robots that other machines can’t do, like searching out nasty compounds or radioactive contamination, gathering microplastic in the oceans, traveling in arteries to scrape out plaque.”
The xenobots were developed using an evolutionary algorithm to create thousands of candidate designs for the new life forms. Attempting to achieve a task assigned by the scientists — like locomotion in one direction — the supercomputer would, over and over, reassemble a few hundred simulated cells into myriad forms and body shapes.
As the programs ran — driven by basic rules about the biophysics of what single frog skin and cardiac cells can do — the more successful simulated organisms were kept and refined, while failed designs were tossed out. After a hundred independent runs of the algorithm, the most promising designs were selected for testing.
To transfer the “in silico” designs into life, the researchers first gathered stem cells, harvested from the embryos of African clawed frogs – i.e., species Xenopus laevis and hence the name “xenobots.” These were separated into single cells and left to incubate. Then, using tiny forceps and an even tinier electrode, the cells were cut and joined under a microscope into a close approximation of the designs specified by the computer.
Assembled into body forms never seen in nature, the cells began to work together. The skin cells formed a more passive architecture, while the once-random contractions of heart muscle cells were put to work creating ordered forward motion as guided by the computer’s design, and aided by spontaneous self-organizing patterns — allowing the robots to move on their own.
The reconfigurable organisms, say the researchers, were shown to be able move in a coherent fashion and explore their watery environment for days or weeks, powered by embryonic energy stores. Turned over, however, they failed, like beetles flipped on their backs. The researchers also tried slicing the xenobots almost in half and report that they stitched themselves up and kept going.
Later tests showed that groups of xenobots would move around in circles, pushing pellets into a central location — spontaneously and collectively. Others were built with a hole through the center to reduce drag. In simulated versions of these, the scientists were able to repurpose this hole as a pouch to successfully carry an object.
Looking ahead, say the researchers, they see their work as one step in applying insights about the biologoical algorithms that determine form and function to both biology and computer science.
“What actually determines the anatomy towards which cells cooperate?” says Levin. “You look at the cells we’ve been building our xenobots with, and, genomically, they’re frogs. It’s 100% frog DNA — but these are not frogs. Then you ask, well, what else are these cells capable of building?”
For more, see “A scalable pipeline for designing reconfigurable organisms.”
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