Study on mechanism of cell damage caused by microbubbles exposed to ultrasound

To elucidate the mechanisms of cell damage caused by microbubbles exposed to ultrasound, two series of experiments were carried out. In one series of experiments, microbubbles and cells were exposed to 1-MHz pulsed ultrasound and observed using a high-speed camera. In another series of experiments, endothelial cells were exposed to ultrasound with and without microbubbles, and the viabilities of the cells were evaluated by fluorescent staining. In the high-speed images, generation of a small stream of the surrounding liquid caused by nonuniform contraction of a microbubble and deformation of a cell beside the bubble were observed. In the cell viability test, the percentage of damaged cells in the presence of microbubbles that had been exposed to ultrasound was significantly higher than that of cells without microbubbles that had been exposed to ultrasound. These results indicated that bubbles exposed to ultrasound causes mechanical stress to act on cells and that this mechanical stress may cause cell injury.