Researchers at Cornell University have developed a chip-based system that generates hydrogen microbubbles on demand and controls their size, number, and position in real time. By combining electrical control with ultrasound, the team can manipulate surrounding fluid, potentially paving the way for reconfigurable microfluidic devices—systems that handle liquids at very small scales—and targeted drug delivery. The study was published in Science Advances.
Using a chip fabricated at the Cornell NanoScale Science and Technology Facility, study author Zhiyuan Zhang generated bubbles with nine tiny electrodes arranged in a square. The experiments involved bubbles measuring 10 to 100 micrometers within a 3-millimeter area. Electricity splits water to produce hydrogen bubbles, which grow larger when voltage is applied for longer. Ultrasound then drives their vibration, transferring energy to nearby liquid. Strong flow depends on matching the ultrasound frequency to the bubbles’ resonant frequency, which is determined by their size. As Cornell physics professor Itai Cohen explained, a bubble that is too large or too small will not vibrate strongly at a given frequency.
The experiments demonstrated flow from both individual bubbles and groups. Equally sized bubbles produced symmetrical flows, whereas the largest bubble governed direction in groups with differing sizes. Changing bubble placement also redirected movement: five bubbles arranged in an L-shape guided liquid along a curve. Higher voltage produced a bubble cloud with rapid flow, which ultrasound could propel in a selected direction. These programmable behaviors could eventually support precise medicine delivery.
