Living tissue instead of metal or plastic – researchers have developed a new version of the so-called “Xenobots”: The small bio-machines are grown from frog stem cells and move using flagella. This allows them to migrate through structures or “sweep” particles together. The bizarre designer beings also heal themselves after injuries and can record information from their environment through a kind of built-in switch system. The prototypes thus illustrate the potential of this unusual robotics concept, say the researchers: For example, highly developed xenobots could one day be used in medicine or environmental protection.
Microscopic “submarines” that are on missions in complex environments or even in the body – this futuristic concept has taken on more and more shape in recent years: Scientists have already constructed small robots with drives and certain capabilities using various technical approaches. The building materials for the tiny ones were mostly metals or plastics and magnetic fields often ensure mobility. But about a year ago an interdisciplinary team of developers presented a concept that demonstrated the advantages of biological building materials and systems: They constructed millimeter-sized robots from living cell tissues of the frog Xenopus laevis, which could produce amazing effects.
“In a way, they have a similar structure to conventional micro-robots. We just use cells and tissues instead of artificial components to create the shape and create predictable behavior, ”says co-author Doug Blackiston of Tufts University in Medford. For the production of the first Xenobots, however, complex puzzle work under the microscope was necessary: The researchers tinkered the tiny pieces individually from skin tissue and equipped them with beating heart cells for the drive. As they now report, their new concept is significantly less complex – but even more effective: The Xenobots 2.0 assemble themselves independently, do not require any muscle cells for movement and are still faster and more durable than the “operationally” assembled predecessor models.
Xenobots 2.0 make themselves mobile
The scientists use the natural development potential of stem cells for production. In the new method, these cells are taken from frog embryos and divided into small units under the microscope, which then develop further in nutrient medium. As the researchers report, the stem cell structures form themselves into small spheres in which some cells then differentiate. Amazingly, so-called cilia form independently on the surface of the structure. These are scourge-like eyelashes that move in a directional manner. In frogs or humans, cilia are usually on the mucous membranes, such as in the lungs, to remove pathogens and other foreign bodies.
On the other hand, they provide the drive on the surface of the spherical Xenobots: Depending on how the structures have developed, the ciliary structures cause a rotation, but in some cases also a directed movement of the small cluster of cells. “This cellular collective shows a remarkable plasticity: Although the genome remains unchanged, a rudimentary new body shape can arise that differs significantly from the standard – in this case the frog body,” says co-author Michael Levin. His colleague Blackiston added. “From a biology perspective, this approach also helps us to understand how cells react to one another when they interact with one another during development, and how we can better control these processes.”
Reporter function and self-healing powers
For use as bio-robots, the researchers used computer systems to identify the xenobots with movement features that can be used. So they can show different behaviors – both individually and in groups. Through experiments, the researchers were able to show that Xenobots with certain properties develop special swarming behavior, for example in order to “sweep together” “dirt particles” in a medium. The experiments showed that they can also move in a directional manner through fine tube systems. Another important aspect of the biological system is that, unlike technical units, the xenobots can heal themselves after damage: if the researchers specifically injured them, the wounds quickly closed again. In addition, they can absorb the energy from the surrounding medium and draw from their supplies, so that they achieve a comparatively long service life, reports the team.
In order to show in principle that the Xenobots can also be equipped with a system for collecting information, the researchers fitted them with a kind of switch. To do this, they used a fluorescent reporter protein called EosFP, which usually glows green. However, when exposed to short-wave light, the protein then emits red light instead of green. To use the effect, the researchers injected the frog embryos with RNA, which leads to the production of the EosFP protein. They then removed the stem cells to create the Xenobots. The mature Xenobots thus carried a detection system for blue light: If they were exposed to this stimulus, they then fluoresced red instead of green. The researchers tested this memory function by letting ten Xenobots swim in a test vessel in which only one point was illuminated with the blue light. Then the red glow indicated that three of the bots had crossed the point – so their “travel experience” had been recorded.
“We want the Xenobots to do useful work. At the moment we’re giving them simple tasks, but ultimately we’re aiming for a new kind of living tool, ”says co-author Josh Bongard of the University of Vermont, Burlington. It is conceivable, for example, that further developed versions could one day recognize radioactive contamination, chemical pollutants or disease states, say the scientists. “It also seems possible to develop Xenobots with more complex behaviors and ability to perform complex tasks,” says Bongard. So it will be interesting to see what will develop from this “living” approach in robotics.
Source: Tufts University, technical article: Science Robotics, doi: 10.1126 / scirobotics.abf1571
Video: Doug Blackiston and Emma Lederer, Tufts University