Key factors that affect sonoporation efficiency in in vitro settings: the importance of standing wave in sonoporation

Ultrasound-induced intracellular drug delivery, sonoporation, is an appealing and promising technique for next generation drug delivery system. Many types of molecules, such as plasmid DNAs, siRNAs and peptides, have been demonstrated to be delivered into the cell by ultrasound with the aid of microbubbles both in vitro and in vivo. Although there are many reports on in vitro sonoporation, the efficiency of successful sonoporation and the viabilities of cells after the procedure documented in each report vary in a wide range, and the reasons for these differences are not fully understood. In this study, we have investigated how different experimental settings would affect sonoporation efficiency and cell viabilities after the procedure. Our results show that the fashion of cell culture (e.g. in suspension or in monolayer culture) and the presence of standing wave have a great impact on the overall results. These results indicate that in vitro sonoporation settings should be carefully evaluated in each experiment. The fact that standing wave is necessary to achieve high sonoporation efficiency may be a problematic issue for clinical application of sonoporation, as it may be difficult (although not impossible) to create standing wave in a human body.