Xenobots: the first living, self-healing robots in the world.
Xenobots are living reconfigurable biobots created using the stem cells of African Clawed frogs (Xenopus laevis). The first designs of the xenobots were created by the University of Vermont in collaboration with Tufts University’s Allen discovery centre.
An individual xenobot is composed of about 500 -1000 cells; making each one of them less than a millimetre (0.04 inches) in size.
How are they made?
According to the computer-simulated designs of xenobots, Vermont researchers recognized that the most suitable building blocks for the creation of these living systems are heart muscle cells and skin cells. Heart muscle cells are able to spontaneously contract and relax while skin cells can provide a more rigid structure. The desired heart muscle cells and skin cells are acquired by incubating stem cells that are capable of developing into different cell types. First, these pluripotent stem cells from early staged (blastula stage) frog embryos were extracted, dissociated and left to incubate precisely to achieve the desired number and types of cells. These derived heart muscle cells and the skin cells from the stem cells of frog embryos are then processed further, merged and set loose in vitro. The newly created xenobots had enough energy to self-locomote up to 10 days in an aqueous environment. But they may function longer if a nutrient-rich medium is provided.
The first designs were in silico!
The first models of the xenobots were designed in silico employing an evolutionary algorithm. The biological passive and the contractile building blocks that simulate skin cells and the heart muscle cells, were combined in a virtual environment and programmed to acquire desired behaviour patterns. Different configurations of building blocks yield different behaviours. First, several random configurations were used. Then the best configurations were selected using an evolutionary algorithm that mimics natural selection.
Those selected configurations were then crafted into xenobots by merging skin cells and heart muscle cells, and their behavioural patterns in vitro were compared against those predicted in the computer simulations. The complete process consists of three basic steps; evolutionary designing in-silico, manipulation in-vitro, and realization in-vivo.
The created xenobots were expected to exhibit four different behaviours; locomotion, object manipulation, object transportation, and collective behaviour.
All the designs successfully exhibited the locomotion behaviour in vivo as predicted in-silico. To determine whether the xenobot’s movement was a result of chance or due to the designs’ evolved geometry and tissue placement, one design was rotated 180° about its transverse plane and evaluated for another 25 times in silico and in vivo. The inverted design showed lesser net displacement compared to the upright design both in silico and in vivo confirming that the desired behaviour does not occur due to chance but due to the precise geometry and tissue placement itself (Figure 4).
Some evolved designs in silico had a hole through the centre of their transverse plan to reduce hydrodynamic drag. This hole was retained as a cavity to store and transport objects.
Moreover, several collective behaviours that were predicted in silico were observed in vivo; when several xenobots were kept together, they entangled, rotated around the same axis, moving towards the same direction. This collective orbital movement proves that xenobots can exhibit grouping behaviour.
Xenobots neither anatomically nor functionally represent traditional robots and they even exhibited self-healing capabilities; when the scientists sliced one robot, it reformed itself and kept moving.
Over time, conventional robots fail and can generate detrimental ecological and health side effects. Xenobots are more environmentally friendly than biological robots, and better for human health.
Possible applications
Xenobots can be used to deliver medication inside the human body, diagnose and destroy diseases such as cancer or even scrape out plaque in human arteries because of the nontoxicity and self-limiting lifespan. They can be further improved to clean up toxic waste and collect ocean microplastics. In addition, their capacity to restore birth defects may have a massive effect on regenerative medicine and developmental biology.
Along with these immediate functional tasks, xenobots may also help researchers to learn more about cell biology. Other than that, immunologically compatible biobots can be improvised out of one’s stem cells using xenobots as a model, contributing to future advancement in personalized medicine.
Ethical concerns
Living cells of Xenopus laevis are being employed to create these reconfigurable biobots. In its true essence, xenobots are genetically identical but anatomically distinct from Xenopus laevis. Though they function as an autonomous unit or an assemblage of living cells with rudimentary cognitive behaviours, they can not be entirely considered as ‘living organisms’, because they cannot reproduce, lack a nervous system rendering them incapable of performing sensory functions -those that are essential characteristics in a living organism. Consequently, it can only be recognized as a novel ‘life form’ without giving rise to a question of proper ethical consideration.
As a result of potential technological advances, if these biobots were to become more sophisticated, more biologically incorporated — even reproductively capable — ethical problems could emerge in the near future!
According to researchers, these novel reconfigurable bio-machines could revolutionize the fields of science and technology including medicine and healthcare in the near future.
