Capture the invisible: illuminating bubble acoustics for medicine*

The visualization of multiphase fluid phenomena poses considerable experimental challenges when the targets are too small, too far, too fast or offer too little optical contrast. Here, we present concrete examples of such events, with a particular focus on ultrafast dynamics of micrometric bubbles, vaporizing droplets and cavitation, all driven by ultrasound and shock waves. Through ultrafast videomicroscopy, laser-based techniques and synchrotron X-ray imaging, we elucidate the beautiful - and occasionally counter-intuitive - physics behind the conversion of acoustic energy to bubble motion. We demonstrate that interfacial instabilities on a bubble surface enable repeated jetting on a targeted substrate, and that acoustic lensing by droplets convert compression waves into tension. The broad objective of this research lies in the quest of harnessing the energy-focusing ability of acoustically driven bubbles and droplets for biomedical applications such as targeted drug delivery and bio-ablation.