Novel, tiny living robots self-assemble from frog cells

Microscopic living robots that can evolve from single cells, maneuver rapidly through different environments in the absence of muscle cells, recall memories, heal themselves when damaged, and exhibit swarm intelligence have been grown using blobs of skin cells from frog embryos.

Xenobots manufactured from frog stem cells are the tiny balls visible in this photo. Photo from Doug Blackiston and Emma Lederer, Tufts University.

Swarms of robots developed from synthetic materials and moving biological systems, called Xenobots, were first described in January 2020. They were named after the frog species Xenophus laevis where the cells came from. Now the team behind these so-called Xenobots has released their version 2.0 which is better in design and more capable than ever.

Biologists from Tufts University in Massachusetts extracted small clumps of skin stem cells from 24-hour-old frog embryos which formed into thousand spheroid structures, as reported in an article titled “A cellular platform for the development of synthetic living machines” in Science Robotics journal as a method for creating Xenobots from frog cells.

“The fundamental findings here is that when you liberate skin cells from their usual context, and you give them a chance to reimagine their multicellularity, they can build other things than what they normally build” corresponding author Michael Levin, Distinguished Professor of Biology at Tufts University said in a press release.

According to him, cells voluntarily take on new roles and create new body plans and behaviors without long periods of evolutionary selection for these features. “We can see that cells can repurpose their genetically encoded hardware, like cilia, for new functions such as locomotion,” he added.

Normally, cilia are utilized to repel pathogens and spread mucous on frog skin, but Xenobots can move around in a coordinated manner with the help of these structures present on their surface.

Compared to the first version (Xenobots 1.0) which relied on the contraction of cardiac cells to produce motion, the upgraded Xenobots 2.0 move across a surface faster, being self-propelled by cilia. Furthermore, version 2.0 live three to seven days longer than their forerunners, which only last for about a week.

“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,” says Douglas Blackiston, PhD, senior scientist and co-first author on the study. “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,” added Emma Lederer, study’s Research Technician.

Team of computer scientists led by Joshua Bonguard at the University of Vermont ran an evolutionary algorithm on the Deep Green supercomputer cluster at the university’s Advanced Computing Core to simulate the behavior of these living machines under various random environmental states. This recognized that a group of individual Xenobots excel at working together to complete a task.

Despite having no nerve cells and brains, Xenobots can traverse through narrow capillaries and curvy paths. When put on a petri dish littered with small particles of iron oxide, these bots can quickly sweep them through and gather them to larger piles while working in a swarm. Xenobots can even self-heal after being cut by sealing themselves back into their spherical shapes.

Xenobots were engineered with a memory capability to record a bit of information. The Tufts biologists used a fluorescent reporter protein called EosFP that glows green, meanwhile the protein emits red light instead when exposed to blue light at 390 nm wavelength.

Prior to the removal of the tissues to create Xenobots, messenger RNA coding for the EosFP protein was injected to the frog embryos’ cells so that the mature Xenobots would have a built-in fluorescent switch that records exposure to blue light.

With the advent of new organisms comes ethical issues. Several attempts at creating living machines previously, at which a wirelessly controlled cockroach is one, have involved manipulating live animals, thus raising ethical concerns. However, Xenobots differ from these because they are made entirely of living cells.

As per Blackiston and Levin, due to the fact that they are created from cells, these bots eventually break apart and are totally biodegradable. Although it is not yet clear what sorts of jobs these Xenobots might do in the future, they hope that they can be used for biomedical and environmental applications.

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CITATIONS

D. Blackiston et al. A cellular platform for the development of synthetic living machines. Science Robotics. Published online March 31, 2021. doi: 10.1126/scirobotics.abf1571.