In what is a remarkable cross between biological life and robotics, a team of scientists has repurposed living frog cells and used them to develop “xenobots.” The cells came from frog embryos, and the xenobots are just a millimeter wide. They are capable of moving towards a target, possibly pick up a payload such as medicine for the inside of a human body, and heal themselves after being cut or damaged.
“These are novel living machines,” according to Joshua Bongard, a computer scientist and robotics expert at the University of Vermont who co-led the new research. “They’re neither a traditional robot nor a known species of animal. It’s a new class of artifact: a living, programmable organism.”
The scientists designed the bots on a supercomputer at the University of Vermont, and a group of biologists at Tufts University assembled and tested them.
“We can imagine many useful applications of these living robots that other machines can’t do,” says co-leader Michael Levin who directs the Center for Regenerative and Developmental Biology at Tufts, “like searching out nasty compounds or radioactive contamination, gathering microplastic in the oceans, traveling in arteries to scrape out plaque.”
The research was published in the Proceedings of the National Academy of Sciences on January 13.
According to the team, this is the first time ever that research “designs completely biological machines from the ground up.”
It took months of processing time on the Deep Green supercomputer cluster at UVM’s Vermont Advanced Computing Core. The team included lead author and doctoral student Sam Kriegman, and they relied on an evolutionary algorithm to develop thousands of different designs for the new life-forms.
When the computer was tasked with completing a task given by the scientists, such as locomotion in one direction, it would continuously reassemble a few hundred simulated cells into different forms and body shapes. As the programs ran, the most successful simulated organisms were kept and refined. The algorithm ran independently a hundred times, and the best designs were picked for testing.
The team at Tufts, led by Levin and with the help of microsurgeon Douglas Blackiston, then took up the project. They transferred the designs into the next stage, which was life. The team gathered stem cells that were harvested from the embryos of African frogs, the species Xenopus laevis. Single cells were then separated out and left to incubate. The team used tiny forceps and an electrode to cut the cells and join them under a microscope into the designs created by the computer.
The cells were assembled into all-new body forms, and they began to work together. The skin cells developed into a more passive build and the heart muscle cells were responsible for creating ordered forward motion as guided by the computer’s design. The robots were able to move on their own because of the spontaneous self-organizing patterns.
The organisms were capable of moving in a coherent way, and they lasted days or weeks exploring their watery environment. They relied on embryonic energy stores, but they failed once flipped over on their backs.
“It’s a step toward using computer-designed organisms for intelligent drug delivery,” says Bongard, a professor in UVM’s Department of Computer Science and Complex Systems Center.
Since the xenobots are living technologies, they have certain advantages.
“The downside of living tissue is that it’s weak and it degrades,” says Bongard. “That’s why we use steel. But organisms have 4.5 billion years of practice at regenerating themselves and going on for decades. These xenobots are fully biodegradable,” he continues. “When they’re done with their job after seven days, they’re just dead skin cells.”
These developments will have big implications for the future.
“If humanity is going to survive into the future, we need to better understand how complex properties, somehow, emerge from simple rules,” says Levin. “Much of science is focused on controlling the low-level rules. We also need to understand the high-level rules. If you wanted an anthill with two chimneys instead of one, how do you modify the ants? We’d have no idea.”
“I think it’s an absolute necessity for society going forward to get a better handle on systems where the outcome is very complex. A first step towards doing that is to explore: how do living systems decide what an overall behavior should be and how do we manipulate the pieces to get the behaviors we want?”
“This study is a direct contribution to getting a handle on what people are afraid of, which is unintended consequences, whether in the rapid arrival of self-driving cars, changing gene drives to wipe out whole lineages of viruses, or the many other complex and autonomous systems that will increasingly shape the human experience.”
“There’s all of this innate creativity in life,” says UVM’s Josh Bongard. “We want to understand that more deeply — and how we can direct and push it toward new forms.”
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