Researchers Create Self-Replicating Living Robots
Professor Joshua Bongard, a computer scientist and robotics expert at the University of Vermont, and his colleagues from Tufts University and Harvard University’s Wyss Institute for Biologically Inspired Engineering — the same team that built the first living robots (Xenobots, assembled from cells of a frog species called Xenopus laevis) in 2020 — have discovered that these computer-designed and hand-assembled organisms can swim out into their tiny dish, find single cells, gather hundreds of them together, and assemble ‘baby’ Xenobots inside their Pac-Man-shaped ‘mouth’ — that, a few days later, become new Xenobots that look and move just like themselves; and then these new Xenobots can go out, find cells, and build copies of themselves.
Kriegman et al. show that clusters of cells, if freed from a
developing organism, can similarly find and combine loose cells into clusters
that look and move like they do, and that this ability does not have to be
specifically evolved or introduced by genetic manipulation. Image credit:
Kriegman et al., doi: 10.1073/pnas.2112672118.
“In a Xenopus laevis frog, these embryonic cells would develop into skin. They would be sitting on the outside of a tadpole, keeping out pathogens and redistributing mucus,” said Professor Michael Levin, director of the Allen Discovery Center at Tufts University.
“But
we’re putting them into a novel context. We’re giving them a chance to
reimagine their multicellularity.”
“People
have thought for quite a long time that we’ve worked out all the ways that life
can reproduce or replicate,” added Dr. Douglas Blackiston, the senior scientist
at Tufts University.
“But
this is something that’s never been observed before.”
In
their earlier experiments, the authors were amazed that Xenobots could be
designed to achieve simple tasks.
Now
they are stunned that these biological objects will spontaneously replicate.
“We
have the full, unaltered frog genome, but it gave no hint that these cells can
work together on this new task, of gathering and then compressing separated
cells into working self-copies,” Professor Levin said.
“These
are frog cells replicating in a way that is very different from how frogs do
it. No animal or plant known to science replicates in this way,” added Dr. Sam
Kriegman, a postdoctoral researcher at Tuft’s Allen Center and Harvard
University’s Wyss Institute for Biologically Inspired Engineering.
On
its own, the Xenobot parent, made of some 3,000 cells, forms a sphere.
“These
can make children but then the system normally dies out after that. It’s very
hard, actually, to get the system to keep reproducing. But with an artificial
intelligence program working on the Deep Green supercomputer cluster at Vermont
Advanced Computing Core, an evolutionary algorithm was able to test billions of
body shapes in simulation — triangles, squares, pyramids, starfish — to find
ones that allowed the cells to be more effective at the motion-based ‘kinematic
replication’ reported in the new research,” Dr. Kriegman said.
“We
asked a supercomputer to figure out how to adjust the shape of the initial
parents, and the AI came up with some strange designs after months of chugging
away, including one that resembled Pac-Man.”
Kinematic
replication is well-known at the level of molecules — but it has never been
observed before at the scale of whole cells or organisms.
“We’ve
discovered that there is this previously unknown space within organisms, or
living systems, and it’s a vast space,” Professor Bongard said.
“How
do we then go about exploring that space? We found Xenobots that walk. We found
Xenobots that swim. And now, in this study, we’ve found Xenobots that
kinematically replicate. What else is out there?”
The
researchers see promise in the research for advancements toward regenerative
medicine.
“If
we knew how to tell collections of cells to do what we wanted them to do,
ultimately, that’s regenerative medicine — that’s the solution to traumatic
injury, birth defects, cancer, and aging,” Professor Levin said.
“All
of these different problems are here because we don’t know how to predict and
control what groups of cells are going to build. Xenobots are a new platform
for teaching us.”
The
team’s work was published in the Proceedings
of the National Academy of Sciences.
_____
Sam
Kriegman et al. 2021. Kinematic self-replication in reconfigurable
organisms. PNAS 118 (49): e2112672118; doi:
10.1073/pnas.2112672118