Correlation of cavitation activity with ultrasound-enhanced delivery of compounds to erythrocytes ex vivo

Abstract

Blood transfusions are one of the most common medical procedures in hospitals, but shortages of erythrocytes often occur due to their limited shelf life (6 weeks) when refrigerated. Preservation of erythrocytes in a dried state offers a potential solution to challenges faced with blood storage, and preservative compounds such as trehalose have been identified in organisms that survive desiccation in nature. However, these compounds do not readily cross mammalian cell membranes. Therefore, we are exploring the use of sonoporation to facilitate their delivery into erythrocytes ex vivo. In this study, we assessed the effect of cavitation activity on delivery of a fluorescent compound similar in size to trehalose (fluorescein) to human erythrocytes. Microbubbles were added to erythrocyte solutions and sonicated (2.5 MHz, 4 cycles) at various pressures and durations. Fluorescence was quantified with flow cytometry. The amplitude of broadband emissions in the first 8 seconds of sonication did not correlate with delivery (r2 = 0.23), whereas after 8 seconds the broadband emissions amplitude was associated with increased delivery to erythrocytes (r2 = 0.97). These results suggest that the timing of cavitation activity, rather than the amplitude alone, may be an important factor in ultrasound-mediated delivery of compounds into erythrocytes.