Modification of the Size Distribution of Lysozyme Microbubbles Using a Post-Sonication Technique

The control of the physical and functional properties of ultrasound responsive microbubbles is of interest because of their potential applications in therapeutic and diagnostic medicine. Crosslinked lysozyme microbubbles, synthesized using high intensity low frequency (20 kHz) ultrasound, possess long-term stability and retain bactericidal property. However, the relatively broader size distribution of these microbubbles may limit their use in some applications. In this article, we introduce a post-sonication technique for modifying the size distribution of lysozyme microbubbles. The post-sonication of these microbubbles at very high ultrasound frequencies (213, 355, 647, and 1056 kHz) led to the selective destruction of microbubbles of certain size range, leading to changes in the size distribution of microbubbles. An increase in acoustic power (10 W-60 W) at a fixed frequency (1056 kHz) resulted in a relatively narrow size distribution of the microbubbles. Although the enzymatic activity of microbubbles was reduced by the post-sonication treatment, significant activity was still preserved.