প্রকাশ: 07/12/2021
Tiny “living machines” made of frog cells can replicate
themselves, making copies that can then go on to do the same. This newly
described form of renewal offers insights into how to design biological
machines that are self-perpetuating.
“This is an incredibly exciting breakthrough,” for the field
of biologically based robotics, says Kirstin Petersen, an electrical and
computer engineer at Cornell University who studies groups of robots. Robots
that can copy themselves are an important step toward systems that don’t need
humans to operate, she says.
Earlier this year, researchers described the behaviors of
the lab-made living robots, called xenobots (SN: 3/31/21). Plucked out of
frogs’ growing bodies, small clumps of skin stem cells from frog embryos
knitted themselves into small spheres and began to move. Cellular extensions
called cilia served as motors that powered the xenobots as they cruised around
their lab dishes.
That cruising can have a bigger purpose, the researchers now
report in the Dec. 7 Proceedings of the National Academy of Sciences. As the
xenobots bumble about, they can gather loose frog cells into spheres, which
then coalesce into xenobots themselves.
This type of movement-created reproduction, called kinematic
self-replication by the researchers, appears to be new for living cells.
Usually, reproducing organisms contribute some parental material to their
offspring, says study coauthor Douglas Blackiston of Tufts University in
Medford, Mass., and Harvard University. Sexual reproduction, for instance,
requires parental sperm and egg cells to get started. Other types of
reproduction involve cells splitting or budding off from a parent.
“Here, this is different,” Blackiston says. These xenobots
are “finding loose parts, sort of like robotics parts in the environment, and
cobbling them together.” Those collections then grow into “a second generation
of xenobots that can move around like their parents,” Blackiston says.
Left to their own devices, spheroid xenobots could generally
create only one more generation before dying out, the researchers found. But
with the help of an artificial intelligence program that predicted an optimal
shape for the original xenobots, the replication could be pushed to four
generations.
The AI program predicted that a C shape, much like an
openmouthed Pac-Man, would be a more efficient progenitor. Sure enough, when
improved xenobots were let loose in a dish, they began scooping up loose cells
into their gaping “mouths,” forming more sphere-shaped bots. A mobile offspring
took shape once about 50 cells had glommed together in a parent’s opening,
Blackiston says. A full-bodied xenobot consists of about 4,000 to 6,000 frog
cells.
Xenobots’ tiny size is an advantage, Petersen says. “The
fact that they were able to do this at such a small scale just makes it even
better, because you can start to imagine biomedical application areas,” she
says. Minuscule xenobots might be able to sculpt tissues for implantation, for
instance, or go inside bodies to deliver therapeutics to specific spots.
Beyond the possible jobs for the xenobots, the research
advances an important science, one that has existential importance for humans,
says study coauthor Michael Levin, a developmental biologist at Tufts. That is,
“the science of trying to anticipate and control the consequences of complex
systems,” he says.
“Originally, no one would have predicted any of this,” Levin
says. “These things are routinely doing things that surprise us.” With
xenobots, researchers can push the limits of the unexpected. “This is about a
safe way to explore and advance the science of being less surprised by things,”
Levin says.
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