Jin Gyun Lee

Researchers at CU Boulder have created tiny, microorganism-inspired particles that can change their shape and self-propel, much like living things, in response to electrical fields.

One day, these shape-shifting “active particles” could be used as microrobots that deliver medications inside the human body, particularly in areas that are hard for drugs to reach on their own, or for building large-scale dynamic materials that are responsive and self-healing.

The findings are described in a new paper published in January 2026 in Nature Communications.

“This discovery opens new possibilities for precise, programmable control of microrobots, enabling them to adapt their motion to different environments or tasks,” said Jin Gyun Lee, a postdoctoral associate in CU’s Shields Lab who co-led the research with Seog-Jin Jeon, a visiting scholar in the Hayward Research Group at the university’s Department of Chemical and Biological Engineering.

How the particles work

Active particles take energy from the surrounding environment and convert it into propulsion. The concept of active particles has been around for decades, but the CU researchers’ particles are among the first that can change their shape and the way they respond to electrical stimulation.

Active particles were originally inspired by microorganisms, according to Lee. So far, most research has used these particles to study how bacteria and other microscopic swimmers move and organize themselves, but newer studies are looking at ways to harness the power of that controlled movement for a variety of applications.

While biological swimmers can change their shape and trajectory to get where they’re trying to go, most active particles developed so far don’t have those capabilities. So the CU researchers aimed to create something a little more lifelike.

“We wanted to bring these systems closer to biology by designing soft, shape-morphing active particles that can bend, reconfigure and ultimately steer themselves,” Lee said.

A microscopic image shows a curled particle transitioning to a straight shape. (Credit: C. Wyatt Shields)

The researchers’ particles measure up to 40 micrometers in length—comparable in size to some larger bacteria and other microorganisms, said Jeon. And they’re made from layers of two very different materials. One layer is a soft hydrogel material that swells and shrinks as it absorbs and releases water, while the other is a hard, glassy substance that does not swell or shrink.

When the surrounding temperature changes, Jeon said, the hydrogel layer changes its size. It absorbs water and swells at cooler temperatures; at warmer temperatures, it releases water and contracts. Because the glassy layer doesn’t change, the difference in swelling between the two layers bends the particle into a new shape.

In the new study, the researchers placed the particles in a chamber filled with water within an AC electrical field. They adjusted the temperature of the water, which caused the particles to change shape and orient themselves in certain directions. The AC electric field then polarized the particles, causing ions within the hydrogel and the surrounding water to start flowing.

This asymmetric ion flow allowed the researchers to propel the particles around in a manner that is controlled by the shape and composition of each layer.

“By adjusting the temperature of the water, we can reversibly alter the shape and effective polarizability of the particles,” Lee said. “This allows us to effectively change the direction and type of propulsion in real time.”

Potential applications

C. Wyatt Shields, the co-principal investigator of the study and an assistant professor in CU’s Department of Chemical and Biological Engineering, said there are many possible uses for his team’s active particles.

Medical microrobots are one possibility for the future. Although they are a new technology and haven’t yet been cleared for use in the human body yet, they could one day be used to deliver drugs, and the researchers’ particles could help steer such microrobots to help them navigate challenging environments.

These robots would need a different way to propel inside the body since running an AC current there might not be safe or practical. But Shields believes the particles could also be used for other applications such as biomedical devices, flexible electronics and sensors.

As a result of this work, Shields and co-principal investigator Ryan Hayward, professor and chair of CU’s Department of Chemical and Biological Engineering, recently received $550,000 in new grant funding from the National Science Foundation (NSF).

“We are very excited about this new NSF-funded project”, Hayward said, “which will allow us to further explore ways to control the motion of single particles as well as to understand the collective behavior of larger groups of particles.”

Said Shields, “We believe this paper opens the door to a new class of active matter that will offer new functional capabilities and take us one step closer toward recapitulating some of the dynamics of living systems, which in turn could help us translate these types of systems toward practical real-world use.”