From clumps of stem cells derived from the African clawed frog, these tiny living machines can be described as somewhere between a living organism and a robot.
Last year, researchers at Tufts University and the University of Vermont (UVM) created self-healing frog cells that moved around, pushed a payload, and even behaved collectively in the presence of a swarm of other frog cells.
The same team now created life forms capable of self-assembling bodies from single cells and moving without muscle cells, and even showing a recordable memory. They also have the ability to navigate different environments, move faster, and last longer than their predecessors. They can still work together as a team and heal themselves if damaged, too. Researchers published their findings in the journal Science Robotics.
Tufts and the University of Vermont have developed a new version of the Xenobots, which is capable of “self-assembling a body from just a single cell, moving without muscle cells, and even recording memories”. These Xenobots are also faster, can navigate more complex environments, can live longer, work together, and can self-heal.
Xenobots, Roll Out!
Tufts described the construction of the first generation Xenobots as “top-down.”. By manually arranging and surgically sculpting cells of the heart and skin, the researchers were able to create tiny biorobots in a variety of shapes.
As a result, their movements were influenced by their shapes, selected with the help of a Xenobots simulator.
Winkler reported that Xenobots could crawl, move in circles, and even partner with other organic bots to accomplish tasks collectively.
The researchers used a bottom-up approach to create Xenobots 2.0, which was published in the journal Science Robotics. Researchers scraped skin stem cells from embryos of frogs, instead of fabricating a frog’s heart and stem cells. Cells on their own merged together to form spheroids when left unattended.
They could live without food for 10 days and even grow if there was sugar added. “We’ve grown them for over four months in the lab,” Tufts’ Doug Blackiston, study co-author, told Science News. “They do really interesting things if you grow them,” including forming new, balloon-like shapes.
New Xenobots were much faster and better at collecting garbage than last year’s models, working together in a swarm to gather iron oxide particles from a petri dish. In addition, they can travel through narrow capillaries or cover large flat surfaces. Additionally, these studies suggest that in the future, in silico simulations may be used to optimize further features of biological bots. Xenobot update includes a feature that can record information.
In robotics, memory is a central feature that can be used to modify the robot’s actions and behavior. Taking this into account, Tufts researchers developed a read/write function onto the Xenobots to record a single bit of information using a fluorescent reporter protein called EosFP, which normally glows green. Upon exposure to light at 390 nm wavelength, the protein however emits red light.
Xenobots are created by injecting the frog embryos with proteins coding for the EosFP protein before cutting out the stem cells. A fluorescent switch is built into the mature Xenobot, which can measure exposure to blue light around 390nm.
A 390nm laser beam was used to illuminate one spot of a surface so that ten Xenobots could swim around that spot to test their memory. They found red lights coming from three bots two hours later. Most of the remaining segments remained green, effectively tracking “travel experiences.”
Future applications of molecular memory could include not only light detection and recording, but also detection of elements such as radiation, chemical pollutants, drugs, or diseases. Adding more functionality to the memory function would enable the bots to record multiple stimuli (more bits of information) or to release compounds or alter behavior in response to stimuli.
Bongard states, “Customized bots can be designed to execute more elaborate tasks when we advance the capabilities of the bots supported by computer simulations.”. It may be possible to design them not only to report conditions in their environment but also to modify and repair them.”
“As far as potential features in the bots are concerned, biological materials offer many possibilities – cells can be sensors and motors, and can transmit and compute information,” Levin explained. In comparison to their metal and plastic counterparts, Xenobots, as well as future versions of biological bots, have the ability to construct their own body plans as their cells grow and mature, and to repair and restore themselves as needed. The ability to heal is a natural characteristic of living organisms, and it is preserved within Xenobot biology.”
Biological robots also have the advantage of metabolism, says Levin. Biological robots are different from metal and plastic robots in that their cells can absorb and break down chemicals, synthesize chemicals and excrete proteins. Rather than reprogramming single-celled organisms to make useful molecules, the whole field of synthetic biology can now be seen as a way of harnessing multicellular organisms.
They were remarkably good at healing and repaired half an inch-long lacerations within 5 minutes thanks to their exceptional ability to heal. All the injured bots ultimately recovered from their injuries, regained their shape, and continued to work.
Life in a new form?
Xenobots’ original work raised questions regarding their existence. Do they have a life?
Robots, made of biological material instead of metal parts?
Thus, it is not surprising that these improved versions – which organize themselves – are already provoking more of the same.
Eva Jablonka, an evolutionary biologist from Tel Aviv University who is not affiliated with the research, told Quanta Magazine they represent a new form of life that is “defined more by what it does than where it belongs developmentally and evolutionarily.”
In addition to providing insight into how ancient single-celled organisms evolved into multicellular organisms, Xenobots and their descendants may also provide evidence of how biological organisms acquire information processing, decision-making, and cognition skills.
To take advantage of the incredible potential of this technology, Tufts University and the University of Vermont have established the Institute for Computer Designed Organisms (ICDO). To make living robots even more advanced, the institute will combine resources from each university and outside sources.
A full description of the biological bots was presented in a TED talk by Michael Levin. In his talk, he mentioned that these tiny biological robots can be useful in tasks of the environment or potentially in therapeutic applications. He also mentioned that these bots can be useful in providing the foundation for regenerative medicine as these bots help in providing evidence on how individual cells come together, communicate, and specialize to create a larger organism, as they do in nature to create a frog or human.
Xenobots and their successors may also provide insight into how multicellular organisms arose from ancient single celled organisms, and the origins of information processing, decision making and cognition in biological organisms.
Main reference: “A cellular platform for the development of synthetic living machines” by Douglas Blackiston, Emma Lederer, Sam Kriegman, Simon Garnier, Joshua Bongard and Michael Levin, 31 March 2021, Science Robotics. DOI: 10.1126/scirobotics.abf1571