Tiny platform creates and directs microbubbles on demand

Source: Cornell Chronicle, written by Kate Blackwood (October 14, 2026). AI-generated summary by biochip.com, published October 15, 2026. Not independently reviewed.

Cornell researchers have built a 3-millimeter chip that creates hydrogen microbubbles exactly where they are needed, then uses ultrasound to make those bubbles direct fluid flow. The programmable platform avoids the usual challenge of trapping and controlling preexisting bubbles. Led by physicists Itai Cohen and Zhiyuan Zhang, the work could help make microfluidic devices and tiny robots more adaptable, including for highly targeted drug delivery.

Making Bubbles Instead of Catching Them

Microbubbles can act like tiny motors in liquid. When energized, they can move fluid, help microscopic robots steer, and generate localized flows. But conventional designs often rely on capturing a bubble in a fixed location, an approach that can be difficult because bubbles are inherently unstable and hard to control.

Cohen's group took a different approach: create a fresh bubble at a chosen electrode whenever it is needed. Their device contains an array of electrodes inside a 3-millimeter area on a chip. Applying voltage adds electrons that split water molecules, producing a hydrogen gas bubble at the tip of an electrode.

The longer the voltage is applied, the larger the bubble becomes. That gives the researchers real-time control over bubble size, number, and position. If a bubble does not work as intended, it can be detached and replaced with a newly formed one.

Ultrasound Sets the Flow

Once a bubble is formed, ultrasound supplies the energy that makes it oscillate. Like pushing a swing at the right moment, the sound must match the bubble's natural resonant frequency, the frequency at which it vibrates most strongly. Those vibrations transfer motion to the surrounding liquid and create flow.

Bubble size is central to this effect. In experiments, the team used nine electrodes arranged in a square, each measuring six microns across. The electrodes produced bubbles between 10 and 100 microns in diameter, and a bubble must be the appropriate size to respond strongly to a given ultrasound frequency.

For example, Cohen noted that a bubble that is too small or too large will not oscillate substantially under ultrasound at 40 kilohertz. A correctly sized bubble, however, can generate much stronger fluid movement. The study, Ultrasound-Driven Electronically Programmable Microbubbles, appeared in Science Advances on Oct. 14.

Programming Bubble Teams

A single resonating bubble can generate a local flow, but groups of bubbles offer more control. Two bubbles of the same size resonate at the same frequency and produce a symmetrical flow pattern. When neighboring bubbles differ in size, one can push fluid more strongly than the other, producing directional flow.

The researchers also demonstrated that the arrangement of active bubbles can program more complex fluid motion. Three bubbles placed in a horizontal row moved liquid from left to right. Three arranged diagonally directed flow upward and leftward, while five bubbles in an L shape produced a curved flow.

Zhang also identified a separate "bubble shooting" behavior. Raising the voltage can produce a cloud of bubbles in a rapid flow, and activating ultrasound then sends that cloud in a selected direction. This adds a way to release bubbles from the chip rather than only using them while attached to electrodes.

Why This Matters

Microfluidics uses channels and tiny volumes of liquid to perform chemical or biological tasks. A platform that can build, erase, and rearrange bubble-powered pumps on demand could make these systems less rigid than devices with permanently fixed components.

The team sees potential for incorporating the bubble-generation circuits into robots. Co-author Alyosha Molnar, a Cornell electrical and computer engineering professor, contributed to the study and will continue the collaboration. Future work will determine how the approach performs in practical robotic and medical settings.

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