Bubbles can be useful tools for microscopic robots, helping them move, steer, create flows of liquid and perform other functions. But designs based on trapping a bubble, a common approach, are unwieldy and unpredictable because bubbles can be hard to catch and control.

“Why are we trying to trap these bubbles?” said Itai Cohen, the Josephson Family Professor of physics in the College of Arts and Sciences (A&S). “Let’s just make them where we want them, when we want them.”

Researchers in Cohen’s lab have developed a way to create and direct microbubbles on demand, without requiring trapping. Set within a 3-millimeter area on a chip, the device produces hydrogen gas bubbles on a grid of electrodes, then powers the bubbles up with acoustic energy through ultrasound. Bubbles resonating on the electrodes can work alone, in pairs or in larger groups to create and direct flows of fluid.