Measurement of cavitation bubble lifetime and size distribution and its correlation with bioeffects

Abstract

Ultrasound-induced disruption of cell membranes can be used to deliver drugs and genes into cells. Because ultrasound bioeffects are governed by cavitation, measurement and control of cavitation bubble lifetime and size distribution should afford greater control over ultrasound’s effects on cells. In this study, 500 kHz ultrasound was focused onto suspensions of albumin-stabilized gas bubbles (Optison) either with or without DU145 prostate cancer cells bathed in calcein. Bubble size and lifetime were determined by Coulter counting, while uptake of calcein and cell viability (i.e., bioeffects) were quantified by flow cytometry. We found that the lifetime and size of Optison bubbles decreased with increasing acoustic energy exposure. Moreover, bioeffects were shown to correlate well with disappearance of bubbles. For example, cell viability remained above 90% until approximately 75% of bubbles were destroyed; viability then dropped dramatically as more bubbles disappeared. Additionally, Optison solutions presonicated to destroy all detectable bubbles also caused significant bioeffects. These observations suggest that bioeffects were caused by the cavitation dynamics of free, short-lived, and/or very small daughter bubbles liberated from albumin-stabilized Optison parent bubbles. Regulation of bubble size distribution, possibly by presonication of Optison solutions, could provide a means to optimize high uptake and cell viability.