Researchers at Cornell University have developed a chip-based system that generates hydrogen microbubbles on demand and uses ultrasound to manipulate surrounding liquid. With real-time control over bubble size, number and position, the team can programme flow using either individual bubbles or groups. The technology could support reconfigurable microfluidic devices, which handle minute quantities of liquid, with potential applications in precise drug delivery. The study was published in Science Advances.
Study author Zhiyuan Zhang used a chip fabricated at the Cornell NanoScale Science and Technology Facility, with nine electrodes arranged in a square. The experiments involved bubbles within a three-millimetre area, ranging from 10 to 100 micrometres in size. Electricity splits water to produce hydrogen, and longer voltage application allows a bubble to grow. Ultrasound then drives the bubbles into vibration, transferring energy to nearby liquid. Bubble size determines the frequency required for resonance: when the applied frequency matches, strong flow results. Cornell physics professor Itai Cohen explained that a bubble exposed to ultrasound at 40 kilohertz must be appropriately sized to vibrate substantially.
The experiments demonstrated several ways to programme movement. Equally sized bubbles can cooperate to produce symmetrical flows, whereas the largest bubble governs flow direction in groups of unequal sizes. Repositioning bubbles can reverse flow, while an L-shaped arrangement of five bubbles can guide it along a curve. Voltage provides another means of adjustment: higher voltage produces a rapidly flowing cloud of bubbles, which ultrasound can propel in a chosen direction.
