Researchers at the University of Colorado Boulder have developed microscopic particles capable of altering their shape and self-propelling in response to electrical fields. These "active particles," inspired by microorganisms, hold potential for various applications, including targeted drug delivery, advanced biomedical devices, and flexible electronics. The findings of this research were published in Nature Communications in January 2026.
Particle Mechanism and Design
Active particles are designed to convert energy from their environment into propulsion. The CU Boulder particles introduce a new capability by combining shape change with a modulated response to electrical stimulation.
The particles, which measure up to 40 micrometers—a size comparable to some larger bacteria—are constructed from two distinct material layers:
- Hydrogel Layer: This soft material expands by absorbing water at cooler temperatures and contracts by releasing water at warmer temperatures.
- Glassy Layer: This hard substance maintains a consistent size regardless of temperature fluctuations.
This layered construction allows the particle to bend into new configurations. Variations in ambient temperature cause the hydrogel layer to change size, and because the glassy layer remains static, this differential swelling or shrinking bends the particle.
In experiments, the microparticles were submerged in water within an AC electrical field. Researchers observed that temperature adjustments caused the particles to alter their shape and orientation. The AC field then polarized the particles, initiating an asymmetric flow of ions within both the hydrogel layer and the surrounding water. This ion flow facilitates particle propulsion, with control over the direction and type of movement achieved by adjusting the water temperature, which reversibly alters the particle's shape and effective polarizability.
Potential Applications
C. Wyatt Shields, a co-principal investigator, identified several potential applications for these active particles:
- Medical Microrobots: Future applications may include systems for targeted drug delivery that can navigate challenging internal bodily environments. Propulsion mechanisms for in-body use would require methods other than AC current.
- Biomedical Devices: Integration into advanced medical equipment.
- Flexible Electronics: Development of adaptable electronic components.
- Sensors: Creation of responsive sensing technologies.
- Dynamic Materials: Building large-scale materials that are responsive and self-healing.
Research Team and Funding
The research was co-led by Jin Gyun Lee, a postdoctoral associate in CU's Shields Lab, and Seog-Jin Jeon, a visiting scholar in the Hayward Research Group. C. Wyatt Shields, an assistant professor, and Ryan Hayward, a professor and chair, both in CU's Department of Chemical and Biological Engineering, served as co-principal investigators.
Shields and Hayward have received a $550,000 grant from the National Science Foundation (NSF). This funding will support further investigation into controlling the motion of individual particles and understanding the collective behavior of larger groups of these microparticles. The research contributes to the development of a new category of active matter, aiming to replicate aspects of living systems' dynamics for practical applications.