Acoustic cavitation-induced shear: a mini-review

Abstract

Acoustic cavitation (or the formation of bubbles using acoustic or ultrasound-based devices) has been extensively exploited for biological applications in the form of bioprocessing and drug delivery/uptake. However, the governing parameters behind the several physical effects induced by cavitation are generally lacking in quantity in terms of suitable operating parameters of ultrasonic units. This review elaborates the current gaps in this realm and summarizes suitable investigative tools to explore the shear generated during cavitation. The underlying physics behind these events are also discussed. Furthermore, current advances of acoustic shear on biological specimens as well as future prospects of this cavitation-induced shear are also described.

Keywords: Acoustics; Microstreaming; Shear.

Fig. 1

Bubble lifetime: nucleation, growth and collapse

Fig. 2

Flowchart enumerating different modes of nucleation, growth, and collapse. The highlighted physical effects are discussed in subsequent sections with temporal, spatial and intensity scales

Fig. 3

Overview of applications (in orange) employing acoustic bubbles with typical magnitudes (blue) and the associated effect (green). Inset shows schematic of acoustic shear with more detailed characteristics

Fig. 4

Frequency dependence of physical effects of acoustic cavitation (McKenzie et al. 2019)

Fig. 5

Effect of power and frequency on the collapse temperature for sonicated water obtained through numerical calculations (Kanthale et al. 2008)

Fig. 6

(a) Effect of ultrasonic power on microjet velocities. Inset shows asymmetric collapse of bubble on a wall, subjected to ultrasound (Wu et al. 2019); (b) phase plot showing different regimes of micro-jetting for $S=1$, side schematic illustrates jet-towards (Fong et al. 2009); (c) schematic of twin bubble-pair near solid wall where bubble 2 is incepted first, allowed to grow and after $\mathrm{\Delta }t$ time-delay, bubble 1 is created. 1 and 2 are used to name bubbles based on their ascending normal distance from the wall

Fig. 7

(a) Effect of driving pressure amplitude on an ambient flow-field around an air bubble attached to a solid boundary in water (kinematic viscosity, $\nu =0$.01 cm²/s); the incident sound pressure was varied from 4.4 mbar to $\left(8.6,\pm ,\mathrm{\Delta }\right)$ mbar; (b) schematic of flow-around free bubble with change in driving pressure amplitude. Used with permission from Elder (1959) and Wu and Du (1997)

Fig. 8

Different microstreaming flow-patterns for single bubble with change in frequency for fixed input power, 30 Vpp. Arrows indicate flow-direction. Used with permission from (Collis et al. 2010)

Fig. 9

Acoustic shear effect on Navicula sp. for different durations. EPS is extracellular polymeric substance. Used with permission from Yatipanthalawa et al. (2021)

Fig. 10

Technological gaps shown by the overlapped regions where better understanding is needed