November 30, 2021

US scientists manufacture first living machines out of frog skin and heart cells

Exciting new uses

The anatomical blueprint for a computer-designed organism and the living organism itself / Sam Kriegman, UVM

A book is made of wood. But it is not a tree. The dead cells have been repurposed to serve another need.

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 a 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.” His research was published earlier this month in the Proceedings of the National Academy of Sciences.

The new creatures were designed on a supercomputer at UVM—and then assembled and tested by biologists at Tufts University. “We can imagine many useful applications of these living robots that other machines can't do,” says co-leader Michael Levin who directs the Center for Regenerative and Developmental Biology at Tufts, “like searching out nasty compounds or radioactive contamination, gathering microplastic in the oceans, traveling in arteries to scrape out plaque.”

The xenobots 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.

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. “It's a step toward using computer-designed organisms for intelligent drug delivery,” says Bongard.

Many technologies are made of steel, concrete or plastic. That can make them strong or flexible. But they also can create ecological and human health problems, like the growing scourge of plastic pollution in the oceans and the toxicity of many synthetic materials and electronics. “The downside of living tissue is that it's weak and it degrades,” say Bongard. “That's why we use steel. But organisms have 4.5 billion years of practice at regenerating themselves and going on for decades.” And when they stop working—death—they usually fall apart harmlessly. “These xenobots are fully biodegradable,” say Bongard, “when they're done with their job after seven days, they're just dead skin cells.”

The scientists see the work presented in their new PNAS study—”A scalable pipeline for designing reconfigurable organisms,”—as one step in applying insights about this bioelectric code to both biology and computer science. “What actually determines the anatomy towards which cells cooperate?” Levin asks. “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?”

Michael Cook is editor of BioEdge.

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