High-speed observation for a better understanding of bubble dynamics in an in vivo -like situation of sonoporation

Abstract

Sonoporation is a technique to temporally increase the permeability of a biological cell membrane by ultrasound exposure and to transduce a foreign gene or drug that normally has no permeability. The mechanisms of sonoporation have not been fully elucidated yet; however, it is widely accepted that microbubbles oscillating adjacent to cells play an important role to induce membrane damage. Dynamics of microbubbles has strong dependence not only on exposure parameters of ultrasound but also on surrounding conditions of the bubbles. To obtain a better understanding of cell-bubble interactions affected by the surrounding conditions, high-speed observation was carried out. A newly designed chamber was used for observation from a lateral direction, enabling visualization of translational movements of bubbles beside a scaffold and of cell-bubble interaction without hiding the interacting point by the oscillating bubble itself. It was observed that a bubble on a soft scaffold surface moves translationally in a direction separating from the surface, whereas a bubble on a hard scaffold surface remains on the surface. Adhesion of a bubble to the top of a cell caused a considerable decrease in bubble oscillation amplitude, but membrane damage was confirmed in all of the observed cells with attached bubbles, indicating the importance of taking into account the conditions surrounding a bubble in order to understand the mechanisms of sonoporation.