Tiny Aquatic Organisms Could Serve as a Model for Robots Required to Move in Complex Environments

The graceful movements of unicellular organisms—Euglena—that acclimatize their body deformations based on the environment, could serve as a model for robots that need to move in challenging situations, for example, debris, soils, or even the human body.

This latest study, performed by SISSA, OGS, Scuola Superiore Sant’Anna, and Universistat Politècnica de Catalunya, has been reported in Nature Physics.

More than three centuries ago, Antoni van Leeuwenhoek, a microscopy pioneer, was enthralled by the microscopic creatures he detected in a drop of water in an adjacent pond. In particular, he was amazed by the behavior of Euglena cells. These creatures spend the majority of their time by swimming in water and they do so by beating their flagellum—this is similar to how most of their peers do.

Yet, at times, Euglena organisms carry out large amplitude, harmoniously coordinated cell body deformations, in a behavior called metaboly. In this context, van Leeuwenhoek was already puzzled as to why these cells engage in repetitions of this graceful gymnastics, which continues to be a mystery even today.

Now, a research team from SISSA and OGS in Trieste, Universistat Politècnica de Catalunya in Barcelona, and Scuola Superiore Sant’Anna in Pisa, demonstrated that metaboly enables Euglena to crawl unusually fast in narrow spaces. This aspect could be a source of motivation for innovative engineering application in the state-of-the-art field of soft robotics. The researchers have reported the results of the study in Nature Physics.

Studying movements using mathematical modeling

Approximately 10 years ago, Marino Arroyo, a professor at Universistat Politècnica de Catalunya and affiliated researcher at IBEC; and Antonio De Simone, a professor at SISSA and at Sant’Anna, were fascinated by the movements of Euglena—an interest driven by stunning amateur videos on YouTube. The duo initially attempted to understand them through mathematical modeling.

We understood the mechanism by which Euglena use their intricate active envelope to perform their peculiar dance, but the central question of why they do it kept bugging us.

Marino Arroyo, Professor and Affiliated Researcher, Universistat Politècnica de Catalunya and IBEC.

The agreement among biologists exploring the Euglena creatures is that metaboly is a functionless vestige gained via evolution from ancestors using it to consume huge prey.

This explanation, however, did not convince us; metaboly just looked too purposeful and elegant to be a remnant of the past.

Antonio DeSimone, Professor, SISSA and Scuola Superiore Sant’Anna.

The fastest crawling cell

“Previous studies and observations suggested that metaboly could be useful to move in crowded environments or narrow spaces.

Giovanni Noselli, Study First Author and Researcher, SISSA

Along with Alfred Beran, a biologist at OGS, Noselli cultured Euglena cells. However, when he placed them in growingly narrow tubes at the SAMBA Lab in SISSA to analyze their response to confinement, he observed that confinement stimulated metaboly, and more prominently, its function became obvious. Cells were able to crawl with remarkable effectiveness and elegance, at approximately one body length every 10 seconds, relatively faster than the fastest crawling animal cells, stated Giovanni Noselli. Integrating hypothetical and computational models, and experimental observations, the authors noted that the metaboly’s peristaltic body deformations enable Euglena cells to push on the fluid surrounding them or the constraining walls in order to move forward.

The study researchers are excited regarding the effect that their physical method could have on biology. The work identifies varied flavors of metaboly in varied species of Euglena based on their locomotion performance.

“Biologists may now ask the question of how these different styles fit into the evolutionary history of Euglena. More intriguingly, we now know that Euglena is an unicellular crawling organism able to move with extreme efficiency in confined environments. However, if or when these cells use this ability in their natural environment remains unclear,” stated Antonio DeSimone.

From Biology to Robotics

Apart from biology, the study can possibly inspire innovative technologies, believe the authors.

The active envelope of Euglena, composed of thin helical elastic strips connected by molecular motors, looks like an engineering marvel.

Marino Arroyo, Professor and Affiliated Researcher, Universistat Politècnica de Catalunya and IBEC.

The study showed that cells follow the principle of “embodied intelligence” to operate. This principle is a new example based on which a soft robot can respond reliably to complex and variable requests by manipulating its flexibility, instead of depending on intricate computations and sensing. “soft robots inspired by Euglena could be devised in the future to move in complex and confined environments including soils, debris, or the human body,” stated Antonio DeSimone.