Researchers from Tampere University in Finland and Anhui Jianzhu University in China have made a significant breakthrough in soft robotics. Their groundbreaking study introduces the first toroidal, light-driven microrobot that can move autonomously in viscous liquids, such as mucus. This innovation marks a major step forward in developing microrobots capable of navigating complex environments, with promising applications in fields such as medicine and environmental monitoring.
A peek through an optical microscope reveals a hidden universe teeming with life. Nature has devised ingenious methods for micro-organisms to navigate their viscous environments: for example, E. coli bacteria employ corkscrew motions, cilia move in coordinated waves, and flagella rely on a whip-like beating to propel themselves forward. However, swimming at the microscale is akin to a human attempting to swim through honey, due to the overwhelming viscous forces.
Inspired by nature, scientists specializing in cutting-edge microrobotic technologies are now on the trail of a solution. At the heart of Tampere University’s pioneering research is a synthetic material known as liquid crystalline elastomer. This elastomer reacts to stimuli like lasers. When heated, it rotates on its own due to a special zero-elastic-energy mode (ZEEM), caused by the interaction of static and dynamic forces.
According to First Author Zixuan Deng, Doctoral Researcher at Tampere University, this discovery not only represents a significant leap forward in soft robotics but also paves the way for the development of microrobots capable of navigating complex environments.
“The implications of this research extend beyond robotics, potentially impacting fields such as medicine and environmental monitoring. For instance, this innovation could be used for drug transportation through physiological mucus and unblocking blood vessels after the miniaturization of the device,” he said.
Here is an exclusive Tech Briefs interview, edited for length and clarity, with Deng.
Tech Briefs: What was the biggest technical challenge you faced while getting this toroidal microrobot to swim?
Deng: Well, there were challenges at pretty much every step of the project. First, we had to optimize the material composition to lower the phase transition temperature of the elastomer. This wasn’t just about cranking up the laser power — it’s a delicate balance. Too much heat could boil the surrounding liquid and cause air bubbles, which would ruin the experiment. Then, there’s the tricky part of choosing the right liquid for the bath. It needs to be highly viscous, optically transparent, and have a high boiling point, which is no small ask.
But I’d say the toughest challenge we faced was forming the elastomeric fiber into a perfectly looped torus, especially when we were working with sizes as tiny as 1-2 millimeters in diameter. Imagine trying to do that manually — it’s incredibly fiddly work! It took a lot of trial and error to get it right, but that’s the kind of problem-solving that makes this work so exciting.
Tech Briefs: Can you explain in simple terms how it works?
Deng: The way the torus starts spinning is all about managing two kinds of frustrations. The first one is a static frustration — it comes from the way the fiber is closed into a loop. That’s fixed once we shape the torus, so it doesn’t change. But then there’s the dynamic frustration, which kicks in when we expose the material to a stimulus like light. This dynamic frustration is like an extra push coming in from a different direction, and we can control how strong it is by adjusting the laser power.
Now, when the combined effect of these frustrations creates enough torque to overcome the system’s losses — things like friction or resistance inside the material — that’s when the magic happens. The torus starts rotating all on its own. It’s fascinating to see it go from a static state to spontaneous motion, all driven by this delicate balance of forces.
Tech Briefs: Do you have plans for future research/work?
Deng: We’re deeply inspired by the collective dynamics we see in living systems, where individual components come together to create something much greater than the sum of their parts. This toroidal structure is an exciting model for exploring many-body interactions because it allows us to study how these dynamics unfold in a controlled setting.
What’s truly remarkable, though, is the torus’s ability to rotate spontaneously — a behavior that comes from what we call a 'zero elastic energy mode.' This autonomy mirrors the out-of-equilibrium nature we find in all biological systems, where nothing is ever truly at rest. Studying these emergent behaviors in artificial systems operating far from equilibrium is both fascinating and incredibly challenging. It’s a frontier where physics, biology, and materials science all intersect, and we’re thrilled to be pushing the boundaries.
Tech Briefs: Do you have any advice for engineers/researchers aiming to bring their ideas to fruition, broadly speaking?
Deng: The idea behind this project actually began a few years ago, but it’s been refined and polished over time to reach the form you see today. It’s truly been a collaborative effort, blending both experimental work and analytical insights.
One thing I’d emphasize is the importance of patience throughout the process. Breakthroughs don’t happen overnight, and staying open to feedback and perspectives from others is just as crucial. Those external opinions often bring fresh ideas and help shape the project in ways you might not have considered on your own.
