Thu. Jan 20th, 2022

Scientists have constructed what they say are the first self-replicating ‘robots’ ever made from living cells.

At first, these freaky-looking ‘xenobots’ might seem remarkable for their superficial resemblance to Pac-Man, but their resemblance to the video game character is probably the least strange thing about them.

These unusual robotic creatures are a spin-off of what the same scientists revealed last year when they unveiled the world’s first robots constructed entirely of living cells – in this case stem cells taken from embryonic frogs.

“These are new living machines,” explained computer scientist and robotics scientist Joshua Bongard of the University of Vermont at the time.

“They are neither a traditional robot nor a known animal species. It is a new class of artifacts: a living, programmable organism.”

Now, Bongard and his collaborators have taken the next step, giving xenobots the opportunity to replicate themselves and create new versions of themselves.

In this case, self-replication is not achieved by the kind of reproduction techniques we normally see in biological life forms.

Instead, the researchers found that if they placed enough of the xenobots in close proximity to each other in a petri dish, their collective motion began to pile up other loose seed cells floating side by side in the solution.

Once enough of these cells were stacked together, the total pile of about 50 cells became a kind of offspring for the xenobot organism, capable of swimming by itself and thus gathering its own offspring.

The phenomenon, called spontaneous kinematic self-replication, has been seen before in other kinds of molecular machines and models, but never before in living multicellular systems like xenobots.

“We find that synthetic multicellular assemblies can also replicate kinematically by moving and compressing dissociated cells in their environment into functional self-copies,” the researchers explain in a new paper describing the reconfigurable organisms.

“This kind of perpetuation, previously unseen in any organism, occurs spontaneously over days rather than evolving over millennia.”

XenobotSimulationAndRealityComparison(Sam Kriegman and Douglas Blackiston)

Above: Simulation (left) actually predicts in vitro self-replication system (right).

To make the self-replicating robots, the researchers extracted pluripotent stem cells from African cleaved seeds (Xenopus laevis) embryonic skin and incubated them in a saline solution, during which time a series of cells would adhere to a spheroid organism and grow cilia on its outer layer, which allowed them to move around.

When a dozen of the first-generation organisms were lost in another bowl along with dissociated stem cells, the movement of the organisms clumped the stem cells into piles, forming a new generation of organisms, which then continued to repeat the same behavior as stacking up cells in heaps.

However, the same dissociated stem cells left alone in solution did not accumulate on their own, indicating that they needed the initial movement of the progenitor xenobots to trigger their formation into aggregated organisms.

That this kinematic self-replication, a behavior never seen before in plants or animals, could occur without genetic modification, shows how radically biological entities can adapt and change in response to their environment, the researchers explained in their paper.

The team also found that they could amplify the phenomenon by using artificial intelligence to simulate conditions that could improve self-replicating behavior.

“Simulations indicated that some body shapes enhanced pile size and rounds of replication, while others attenuated or stopped self-replication,” the researchers explain. “Some but not all geometries were better than the spheres.”

In the end, the semitorus shape (Pac-Man in 3D, basically) was the best candidate to stack loose seed cells into new organisms, and changes in the environment – the introduction of walls that restrict the movement of xenobots – also helped.

While we are still very much at the beginning of tinkering with these living robotic creatures, scientists say that the unusual organisms may one day perform useful work if we can continue to figure out how they work and also decide the real jobs to give them.

“This suggests that future technologies, with a little external guidance, may become more useful as they spread,” the team explains, “and that life contains surprising behaviors just below the surface waiting to be revealed.”

The results are reported in PNAS.

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