Interaction of ultrasound driven microbubbles and lipid membrane

Micron‐sized bubbles show pronounced oscillations when submitted to ultrasound, leading to increased scattering and improved echographic contrast. It has been reported that this excitation can also alter nearby cell membranes [M. Ward, J. Wu, and J. F. Chiu, Ultrasound Med. Biol. 26, 1169–1175 (2000)], and increase the permeability for drug delivery. To elucidate the mechanisms at work in these sonoporation experiments, we developed a setup that allows for a controlled study of the interaction of single microbubbles with single lipid bilayer vesicles. Substituting vesicles for cell membranes is advantageous because the mechanical properties of vesicles are well‐known. Microscopic observations reveal that vesicles near a bubble undergo vivid motion, being periodically accelerated toward and away from the bubble. This ‘‘bouncing’’ of vesicles is a vivid motion that we attribute to a streaming flow field set up by the bubble oscillation. Some vesicles undergo dramatic deformations as they follow the flow, reflecting the high shear rates attained. Break‐up of vesicles could also be observed.