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Researchers at the University of Colorado Boulder have created a new way to build and control tiny particles that can move and work like microscopic robots, offering a powerful tool with applications in biomedical and environmental research.

The published in Nature Communications, describes a new method of fabrication that combines high-precision 3D printing, called two-photon lithography, with a microstenciling technique. The team prints both the particle and its stencil together, then deposits a thin layer of metal—such as gold, platinum or cobalt—through the stencil's openings. When the stencil is removed, a metal patch remains on the particle.

The particles, invisible to the naked eye, can be made in almost any shape and patterned with surface patches as small as 0.2 microns—more than 500 times thinner than a human hair. The metal patches guide how the particles move when exposed to electric or magnetic fields, or chemical gradients.

"The shape of surface patches gives particles information about where to go," said Assistant Professor Wyatt Shields, one of the paper's authors. "We've not had good methods to control the shape of those patches until now."

With this control, these particles could potentially help improve how drugs spread through human organs, improving the drug's overall effectiveness, or aid in the removal of pollutants from contaminated environments.

The research team includes first author Kendra Kreienbrink, a materials science and engineering Ph.D. student in the Shields Lab, along with two undergraduate students: Zoe Cruse, majoring in chemical and biological engineering and computer science, and Alisha Kumari, in biomedical engineering.

"This paper not only represents the exciting things that can be accomplished in active particles and microrobots using nonconventional microfabrication," Shields said, "but that the inclusion and mentorship of undergrads early in research can lead to innovative outcomes."