A four-legged xenobot moving in its aquatic environment.
Image: Douglas Blackiston, Tufts University

With the help of a supercomputer, scientists have built tiny machines comprised entirely made of biological materials. Able to survive for days and even weeks, these xenobots could eventually be used to deliver drugs inside the body and to clean up the environment.

New research published in Proceedings of the National Academy of Sciences describes the xenobot—a “reconfigurable organism” designed by a collaborative team from Tufts University, the University of Vermont, and the Wyss Institute at Harvard.

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“These are novel living machines,” said Joshua Bongard, a roboticist from the University of Vermont and a co-leader of the new study, in a press release. “They’re neither a traditional robot nor a known species of animal. It’s a new class of artifact: a living, programmable organism.”

That the authors describe their creation as “organisms,” “living machines,” and “lifeforms” is bold, given these artificial creatures can’t reproduce, feed themselves, or respond to external stimuli, among other requirements for life. At the same time, however, these xenobots are remarkably lifelike in that they’re comprised entirely of biological materials, feed off energy supplied by their cells, move with intent, and even repair their injuries. We can certainly quibble about whether or not these robots qualify as being truly alive, but they’re most certainly a precursor to fully formed artificially constructed lifeforms.

But we’re getting a bit ahead of ourselves. These xenobots, which measure around a millimeter wide, could be immensely helpful even in this basic, preliminary form. They could eventually deliver drugs inside the body, assist with environmental remediation, and even improve our understanding of biology itself, according to the researchers. In the press release, Tufts University researcher and study co-author Michael Levin said the xenobots could hunt for “nasty compounds or radioactive contamination,” gather microplastics in the oceans, and travel inside “arteries to scrape out plaque.”

And because these robots are made entirely from cells, rather than steel or plastic, they’re biodegradable by default. Large fleets of xenobots could be sent out into the environment or inside the human body to do their work, and then simply deteriorate like any other biological cells once their task is complete. An advanced version of the xenobots, perhaps aided with molecular nanotechnology or bioengineered bacteria, could convert unwanted materials into an inert, harmless form.

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Top: Computer-generated xenobot designs. Bottom: The lab-grown xenobots, made from cells.
Image: UVM

The xenobots were initially designed by a supercomputer housed at the University of Vermont. Using an evolutionary algorithm, the researchers devised thousands of possible designs for their novel lifeform, with the capacity for unidirectional locomotion being a fundamental physical requirement. To do this, the algorithm took hundreds of simulated cells and reconfigured them in various ways until the most viable solutions emerged.

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The best candidates were then built and tested at Tufts University. There, the scientists acquired their basic biological building blocks by extracting stem cells from African frog embryos, specifically Xenopus laevis, which is where the name xenobots comes from. Specialized cells were then grown and meticulously assembled to match the form designed by the computer. Hardy skin cells provided the basic structure, and heart muscle cells, which spontaneously contract and expand, provided the means of locomotion.

Left: A xenobot blueprint produced by the evolutionary algorithm, in which green shows skin cells and red shows heart muscle cells. Right: the “living” xenobot inspired by the computer’s design.
Image: Sam Kriegman, UVM

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In tests, the xenobots were able to move around their aquatic environment for days, sometimes even weeks, depending on how much energy was available in their cells, without additional nutrients being added to the environment. Importantly, the bots were able to move in a single direction and even push pellets toward a central location. One design allowed for a pouch, inside of which chemicals, such as medicine, could eventually be stored for the purpose of delivery.

In a test to see what would happen when a xenobot was cut almost entirely in half, the bot automatically stitched itself together and was able to get back on track. This sort of “spontaneous behavior cannot be expected from machines built with artificial materials unless that behavior was explicitly selected for during the design process,” wrote the authors in the paper.

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Tara Deans, a biological engineer and an assistant professor from the University of Utah who wasn’t involved with the new study, told Gizmodo that the achievement was significant because the authors “used the power of biology” to create “a ‘living machine’ based on the parameters they set,” namely the goal of movement. Deans is particularly excited by the prospect of programmable organisms, which would let scientists encode instructions to biodegrade after a specified amount of time or when the bot senses an appropriate environment in which to degrade.

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“The examples of applications are endless,” wrote Deans in an email to Gizmodo. “Certainly this is a proof-of-concept paper, and there’s still a lot of work to do to get to major applications,” she said, adding that there’s “no Frankenstein story here.”

Indeed, the ability to build novel organisms from scratch might seem a bit hubristic and scary—and no doubt, we’ll eventually have to monitor and regulate these biological inventions as they become more advanced—but the benefits are simply too important to ignore.  

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