Scientists Revealed Brine Shrimp’s Swimming Secrets Could Help Tiny Robots Deliver Drugs to Tumors

Imagine tiny swimmers, smaller than the width of a human hair, gracefully moving through water in ways that defy our everyday understanding of physics. These aren’t just microscopic organisms or particles—they belong to a special realm called the mesoscale, bridging the gap between the microscopic and macroscopic worlds. Now, physicists at Aalto University are uncovering how these small creatures swim so efficiently, paving the way for microscopic robots capable of delivering drugs directly inside the human body.

What is the Mesoscale?

Physics is often divided into different scales. In the macroscopic world—the world of humans, cars, and planets—motion is dominated by inertia, the tendency of objects to keep moving unless acted on by a force. In the microscopic world—think bacteria and molecules—viscosity dominates, meaning that water feels almost like honey and tiny organisms must work hard to move.

The mesoscale sits in between these two extremes. Here, neither inertia nor viscosity alone explains how objects move. Forces from both realms interact in complex ways, requiring new physics to describe motion. Surprisingly, nature has already solved many of these challenges. Tiny organisms like small larvae, shrimp, and Artemia (commonly known as brine shrimp) navigate this world with incredible efficiency—but until recently, scientists didn’t fully understand how.

The Discovery: How Mesoscale Organisms Swim

Researchers at Aalto University’s Department of Applied Physics, led by Assistant Professor Matilda Backholm, set out to study how mesoscale organisms swim. Their work was recently published in the journal Communications Physics and provides fascinating insights into the physics of movement at this scale.

The team focused on Artemia, tiny creatures ranging from 400 to 1,500 micrometers long—just under 2 millimeters at their largest. Using a specially developed micropipette force sensor, they were able to measure the forces exerted by Artemia as they swam in water, without harming the creatures.

During their observations, the researchers noticed a unique motion: Artemia flexed a joint in their antennae, tracing a figure-eight pattern as they moved. This motion, explained doctoral researcher Sharadhi Nagaraja, added a degree of freedom to the organism’s movement and revealed a remarkable physical principle at work: time reversal symmetry breaking.

Time Reversal Symmetry: Swimming Physics Explained

Time reversal symmetry is a concept from physics that is crucial in very viscous environments. Simply put, if you film a microscopic organism swimming, its motion must look different when the video is played forward versus backward. If it looks the same in both directions, the organism cannot move forward—meaning swimming at tiny scales requires careful coordination.

At the mesoscale, this rule is less strict. Organisms like Artemia don’t need to break time reversal symmetry to swim, but interestingly, they do. The researchers found that when Artemia performed more asymmetric, non-reciprocal motions with their antennae, they swam faster and with greater force.

“This is the first time anyone has directly measured this phenomenon in a living organism,” said Nagaraja. “We were able to connect the physics principle directly to how well the organism swims.”

To analyze the complex swimming patterns, the team used machine learning, tracking countless frames of movement and measuring forces in real time. This combination of biology and physics allowed them to map out the hidden mechanics behind meso-swimming—a task that has challenged scientists for decades.

From Nature to Technology: Mesorobots on the Horizon

Understanding mesoscale swimming is not just an academic curiosity—it has the potential to revolutionize medicine. According to Backholm, the principles discovered in Artemia could inform the design of mesorobots: tiny, programmable robots that move inside the human body.

“Imagine robots small enough to travel through blood vessels, delivering drugs directly to a tumor or a damaged organ,” Backholm explains. “Instead of spreading medication throughout the entire body and risking side effects, these robots could carry precise doses exactly where they are needed. They could also transport more medicine than microscopic alternatives like nanoparticles.”

Such robots would rely on the same principles as Artemia: efficient, non-reciprocal motion at the mesoscale. Engineers can mimic the figure-eight antenna motion or other asymmetric patterns to optimize propulsion in tiny fluid environments.

Backholm emphasizes that this is a rare case where science is catching up with nature. Over millions of years, evolution has perfected the swimming mechanics of small organisms. Now, engineers are learning how to translate these biological strategies into technology.

Why Mesoscale Research Matters

The research has multiple implications:

1. Medical Applications: Targeted drug delivery could become safer and more efficient. Mesorobots could also assist in minimally invasive procedures, like clearing clots or delivering regenerative therapies.

2. Fundamental Physics: The study helps fill a gap in understanding forces at the mesoscale, a realm where neither classical nor microscopic physics fully explains motion.

3. Robotics and Engineering: Designing robots for complex environments—inside the body, in oceans, or even in microfluidic devices—requires a deep understanding of how forces interact at small scales. Mesoscale research provides that foundation.

4. Machine Learning in Biology: The combination of physics, biology, and AI allows scientists to analyze highly complex systems, bridging gaps that were previously impossible to quantify.

The Road Ahead

While the discovery is exciting, it’s just the beginning. Backholm and her team are now exploring how different mesoscale organisms achieve efficient swimming and how these principles can be adapted for robotic applications. They are also refining the micropipette force sensor technique, which allows precise measurements of living organisms in motion.

“Nature has already solved many of these problems,” Backholm says. “Our job is to learn from it and apply it. The better we understand the physics of meso-swimming, the more we can engineer solutions for medicine, robotics, and beyond.”

The research represents a convergence of multiple fields: physics, biology, engineering, and artificial intelligence. By studying how tiny creatures navigate their fluid world, scientists are laying the groundwork for a new generation of tiny robots that could one day swim through the human body, delivering life-saving treatments with unprecedented precision.

Conclusion

The mesoscale world is a fascinating frontier where the rules of physics are both familiar and strange. Organisms like Artemia demonstrate that efficiency in movement is not just about speed or size, but about the clever application of asymmetric, time-breaking motion. By uncovering these secrets, researchers are opening the door to mesorobots, microscopic machines capable of transforming healthcare.

This research is a vivid reminder that nature often solves problems before humans even realize they exist. As Backholm puts it, evolution has been perfecting swimming mechanics for millions of years. Now, armed with new tools and interdisciplinary expertise, humans are finally beginning to understand—and perhaps replicate—these extraordinary feats.

The study by R. A. Lara et al., published in Communications Physics (2026), DOI: 10.1038/s42005-025-02486-3, marks a significant step toward bridging the gap between fundamental physics and practical medical applications. The tiny swimmers of the mesoscale may one day inspire a revolution in drug delivery, robotic engineering, and beyond.