The same team of biologists and computer scientists from Tufts University and the University of Vermont that created the “Xenobots” last year have now developed Xenobots 2.0. Last year’s version were novel, tiny self-healing biological machines created from frog cells, and they could navigate, push payloads, and act as a collective unit in some cases.
The new Xenobots 2.0 are life forms that can self-assemble a body from single cells. They do not require muscles to move, and they have even demonstrated recordable memory. Compared to their previous counterparts, the new bots move faster, navigate even more environments, and have longer lifespans. At the same time, they can still work together and heal themselves when damaged.
The new research was published in Science Robotics.
With the Xenobots 1.0, the millimeter-sized automations were constructed “top down,” with the manual placement of tissue and surgical shaping of frog skin and cardiac cells, which produces motion. With the new version of the technology, they were constructed “bottom up.”
Stem cells were taken from the embryos of the African frog called Xenopus laevis, and this enabled them to self-assemble and grow into spheroids. After a few days, the cells differentiated and produced cilia that moved back and forth or rotated in a specific way.
These cilia provide the new bots with a type of “legs” that enables them to rapidly travel across surfaces. In the biological world, cilia, or tiny hair-like projections, are often found on mucous surfaces like the lungs. They help by pushing out foreign material and pathogens, but in the Xenobots, they offer rapid locomotion.
Michael Levin is a Distinguished Professor of Biology and director of the Allen Discovery Center at Tufts University. He is the corresponding author of the study.
“We are witnessing the remarkable plasticity of cellular collectives, which build a rudimentary new ‘body’ that is quite distinct from their default — in this case, a frog — despite having a completely normal genome,” said Levin. “In a frog embryo, cells cooperate to create a tadpole. Here, removed from that context, we see that cells can re-purpose their genetically encoded hardware, like cilia, for new functions such as locomotion. It is amazing that cells can spontaneously take on new roles and create new body plans and behaviors without long periods of evolutionary selection for those features.”
Senior scientist Doug Blackiston was co-first author of the study along with research technician Emma Lederer.
“In a way, the Xenobots are constructed much like a traditional robot. Only we use cells and tissues rather than artificial components to build the shape and create predictable behavior.” said Blackiston “On the biology end, this approach is helping us understand how cells communicate as they interact with one another during development, and how we might better control those interactions.”
Over at UVM, the scientists were developing computer simulations that modeled different shapes of the Xenobots, which helped identify any different behaviors that were exhibited in both individuals and groups. The team relied on the Deep Green supercomputer cluster at UVM’s Vermont Advanced Computing Core.
Led by computer scientists and robotics expert Josh Bongard, the team came up with hundreds of thousands of environmental conditions through the use of an evolutionary algorithm. The simulations were then used to identify Xenobots that could work together in swarms to gather debris in a field of particles.
We know the task, but it’s not at all obvious — for people — what a successful design should look like. That’s where the supercomputer comes in and searches over the space of all possible Xenobot swarms to find the swarm that does the job best,” says Bongard. “We want Xenobots to do useful work. Right now we’re giving them simple tasks, but ultimately we’re aiming for a new kind of living tool that could, for example, clean up microplastics in the ocean or contaminants in soil.”
The new version of the bots are faster and more efficient at tasks like garbage collection, and they can now cover large flat surfaces. The new upgrade also includes the ability for the Xenobot to record information.
Recording Memory and Self-Healing
The most impressive new feature of the technology is the ability for the bots to record memory, which can then be used to modify its actions and behaviors. The newly developed memory function was tested and the proof of concept demonstrated that it could be extended in the future to detect and record light, the presence of radioactive contamination, chemical pollutants, and more.
“When we bring in more capabilities to the bots, we can use the computer simulations to design them with more complex behaviors and the ability to carry out more elaborate tasks,” said Bongard. “We could potentially design them not only to report conditions in their environment but also to modify and repair conditions in their environment.”
The new version of the robots are also able to self-heal very efficiently, demonstrating that they are capable of closing the majority of a severe full-length laceration half their thickness within just five minutes.
The new Xenobots carry over the ability to survive up to ten days on embryonic energy stores, and their tasks can be carried out with no additional energy sources. If they are kept in various different nutrients, they can continue at full speed for months.
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