Improvement in microhollow production using bubble cloud cavitation by dual-frequency ultrasonic wave irradiation

Bubble cloud cavitation plays an important role in sonoporation, which produces microhollows on the cell membrane using a microjet. However, it has complicated mechanisms and the optimization of the ultrasonic wave irradiation sequence is difficult. The optimization of an ultrasonic wave irradiation sequence, which allows for effective bubble cloud cavitation, is very important for producing high-quality microhollows. Thus, it is necessary to clarify the mechanism of cavitation for different-frequency ultrasonic waves. In this study, we evaluate bubble cloud cavitation for ultrasonic wave irradiations of different frequencies. The observation of bubble cloud dynamics using a high-speed camera and of microhollows using a confocal laser microscope are performed in this study. From these results, a novel ultrasonic wave irradiation sequence that uses two ultrasonic waves with different frequencies is proposed. (C) 2014 The Japan Society of Applied Physics