Bubbles with shock waves and ultrasound: a review

Abstract

The study of the interaction of bubbles with shock waves and ultrasound is sometimes termed ‘acoustic cavitation'. It is of importance in many biomedical applications where sound waves are applied. The use of shock waves and ultrasound in medical treatments is appealing because of their non-invasiveness. In this review, we present a variety of acoustics–bubble interactions, with a focus on shock wave–bubble interaction and bubble cloud phenomena. The dynamics of a single spherically oscillating bubble is rather well understood. However, when there is a nearby surface, the bubble often collapses non-spherically with a high-speed jet. The direction of the jet depends on the ‘resistance' of the boundary: the bubble jets towards a rigid boundary, splits up near an elastic boundary, and jets away from a free surface. The presence of a shock wave complicates the bubble dynamics further. We shall discuss both experimental studies using high-speed photography and numerical simulations involving shock wave–bubble interaction. In biomedical applications, instead of a single bubble, often clouds of bubbles appear (consisting of many individual bubbles). The dynamics of such a bubble cloud is even more complex. We shall show some of the phenomena observed in a high-intensity focused ultrasound (HIFU) field. The nonlinear nature of the sound field and the complex inter-bubble interaction in a cloud present challenges to a comprehensive understanding of the physics of the bubble cloud in HIFU. We conclude the article with some comments on the challenges ahead.

Spiral computed tomography evaluation of rabbit VX2 hepatic tumors treated with 20 kHz ultrasound and microbubbles

“…Thus, CT is a useful tool to evaluate liver cancer therapy and tumor necrosis, and to measure the exact area of a tumor. The present study used 20 kHz US, which is the lowest frequency point on the US wave (30). This frequency was selected as higher sound frequencies accelerate the vibration of the MB in the sound field while reducing the amplitude (31).…”

Sonobactericide: An Emerging Treatment Strategy for Bacterial Infections

“…The acoustic pressure required to initiate inertial cavitation can be higher than the pressure required for stable cavitation (Bader and Holland 2013) and also depends on fluid properties and the cavitation nuclei (Apfel 1997). Inertial cavitation forms microjets (Ohl et al 2015) that can damage or deform the biofilms (Goh et al 2015). Administration of cavitation nuclei can reduce the cavitation threshold (Bader and Holland 2013).…”

“…At a higher pressure (0.7 MPa, 1 MHz, 50-ms pulse), a 7.4-mm SonoVue microbubble had an extremely large radial excursion (R max = 27.3 mm) with a liquid jet within that led to mechanical dislodgement of the bacteria from the biofilm. The direction of a jet with respect to the surface of the biofilm depends on the elasticity of the surface (Ohl et al 2015). Accordingly, jet formation can create substantial shear force leading to either an indentation or an invagination of the surface (Chen et al 2011(Chen et al , 2012.…”

Targeting Taxanes to Castration-Resistant Prostate Cancer Cells by Nanobubbles and Extracorporeal Shock Waves

“…In fact, combined treatment with paclitaxel-loaded NBs and ESWs reduced cell migration of more than 85% with respect to treatment with paclitaxel alone; whereas docetaxel-loaded NBs and ESWs reduced cell migration of more than 82% with respect to treatment with docetaxel alone. The enhancement of cytotoxicity and migration inhibition may be the consequence of cavitation which occurs when acoustic waves propagate into fluids [31]. In fact, cavitation determines both transient permeabilization of plasma membranes, thus allowing drug penetration into the cells, as well as the perturbation of the NBs, resulting in the intracellular drug release.…”