Xenobots: Cell-Based Living Robots That Can Self-Replicate

Preserved tadpoles of a frog named Frankixalus jerdonii, a new genus of frogs, are seen at Systematics Lab at the University of Delhi, Department of Environmental Studies, in New Delhi. Stem cells of another species, Xenopus laevis, is taken to generate xenobots on Jan. 14, 2016. Altaf Qadri/AP Photo

Swarms of tiny living robots have discovered the ability to self-replicate, i.e. reproduce, through the process of gathering single cells and assembling them together to form new organisms, through a unique process not seen until now in plants or animals, scientists say.

Researchers Sam Kriegman, Douglas Blackiston, Michael Levin, and Josh Bongard from Tufts University, Harvard, and the University of Vermont created the life forms, called xenobots, in 2020, using stem cells taken from the embryo of the African clawed frog, Xenopus laevis.

Unspecialized cells that have the capability to evolve into different types of cells are known as stem cells. Researchers scraped off living stem cells from frog embryos and incubated them without manipulating the genes in order to create xenobots.

Xenobots aren’t technically robots, which are commonly understood to be constructed of inorganic matter, but are named as such because of their ability to act on behalf of humans, according to researcher Bongard.

These frog-celled life forms are less than a millimeter—0.04 inches—wide, and under the right lab conditions have been observed moving around in their environments, working together in groups, and self-healing. Researchers have now discovered that the creatures can self-replicate as well through an entirely new form of biological reproduction.

“They find and combine building blocks into self-copies. Here we 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,” according to the research article.

Formation of Xenobots

When the stem cells are placed in a saline solution, they form into sphere-shaped clumps of approximately 3,000 cells around half a millimeter wide. The clumps are then covered in cilia, hair-like structures that help the xenobots move, propelling the cilia in an oar-like motion, according to the article.

Xenobot clumps, when placed in dishes with disassociated stem cells, work together and gather loose cells into piles, which then form new xenobots, in a process known as spontaneous kinematic self-replication.

“In short, progenitors build offspring, which then become progenitors,” the study states.

Each reproductive cycle produces slightly smaller xenobot offspring, eventually ending in clumps with less than 50 cells that can’t swim or replicate further.

Maximum Efficiency Using AI

The researchers then made use of artificial intelligence and tested billions of potential xenobot shapes that maximize replication rate. They found that C-shaped clumps are most effective at gathering loose cells, as the mouth collects and moves cells more easily.

This algorithmic improvement resulted in Pac-Man-shaped xenobots reproducing four generations, twice more than spherical-shaped xenobots.

“By manipulating the shape of the parents, you can make a better shovel to move more cells,” Bongard told New Scientist.

According to researchers, xenobots and their newly discovered reproductive mechanisms can be utilized in various ways, for example, gathering microplastics in the oceans or inspecting root systems.

Regarding concerns of self-replication, the scientists said that the experiments were regulated by ethics experts and the living organisms were contained within the lab environment.

“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,” Levin wrote in a University of Vermont report.

“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.”