Frog skin cells have turned into living machines – scientists


Using pieces of skin cells from frog embryos, scientists have grown creatures unlike anything else on Earth, a new study reports. These microscopic “living machines” can swim, sweep away debris, and heal themselves after a wound.

Scientists often seek to understand the world as it exists, says Jacob Foster, a collective intelligence researcher at the University of California, Los Angeles, who is not involved in the research. But a new study published on March 31 in Science Robotics , is part of a “liberating moment in the history of science,” says Foster. “Reorientation to what is possible.”

In a sense, the bots were self-made. Scientists extracted small clumps of skin stem cells from frog embryos to see what the cells would do on their own. Separated from their normal locations in the growing frog embryo, the cells organized into balls and grew. After about three days, the clusters, called xenobots, began to float.

Normally, hair-like structures called cilia on frog skin repel pathogens and spread mucus around. But on xenobots, eyelashes allowed them to move. This remarkable development “is a great example of how life reuses what’s at hand,” says study co-author Michael Levin, a biologist at Tufts University in Medford, Massachusetts.

A swarm of xenobots (bright spots) swims around and pushes small particles. DOUGLAS BLACKISTON

And this process happens quickly. “This is not some effect where evolution has found a new application over hundreds of thousands of years,” Levin says. “It happens before your eyes for two or three days.”

Xenobots have no nerve cells and no brain. However, the xenobots—each about half a millimeter wide—can swim through very thin tubes and navigate winding mazes. If placed in an arena littered with small particles of iron oxide, the xenobots can sweep the debris into piles. Xenobots can even heal themselves; after cutting, the bots return to their spherical shape.

Scientists are still developing the fundamentals of xenobot life. Animals can live for about 10 days without food. When fed sugar, xenobots can live longer (although they don’t grow). “We grew them for over four months in the lab,” says study co-author Doug Blackiston, also at Tufts. “They do really interesting things when you grow them,” including forming strange balloon-like shapes.

microscopic image of a xenobot
This xenobot is approximately 500 micrometers across and is made of frog cells, although it looks and acts nothing like a real frog.DOUGLAS BLACKISTON

It is not yet clear what, if any, work these xenobots might be doing. Clearing waterways, arteries or other small spaces comes to mind, the researchers say. More broadly, these organisms can teach lessons about how bodies are built, Levine says.

Ethical issues arise with the emergence of new organisms, warns Coby Lanes, a digital ethics researcher at the University of Melbourne in Australia. “Scientists like to create things and don’t necessarily think about the consequences,” she says. More conversations about unintended consequences are needed, she says.

Levine agrees. The little xenobots are fascinating in their own right, he says, but they raise bigger questions and open up more possibilities. “It’s a search for a whole galaxy of new weird things.”

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