Acoustic microbubble propulsion, train-like assembly and cargo transport.

Achieving controlled mobility of microparticles in viscous fluids can become pivotal in biologics, biotechniques, and biomedical applications. The self-assembly, trapping, and transport of microparticles are being explored in active matter, micro and nanorobotics, and microfluidics; however, little work has been done in acoustics, particularly in active matter and robotics. This study reports the discovery and characterization of microbubble behaviors in a viscous gel that is confined to a slight opening between glass boundaries in an acoustic field.

Nonlinear dynamics of a solid particle in an acoustically excited viscoelastic fluid. II. Acoustic radiation force.

An analytical formula is derived for acoustic radiation force exerted by an axisymmetric acoustic wave on an isotropic solid spherical particle in a compressible viscoelastic fluid. The particle is assumed to undergo pulsation, translation, and shape deformations of all orders. The fluid motion is described by the compressible Oldroyd-B model.

Nonlinear dynamics of a solid particle in an acoustically excited viscoelastic fluid. I. Acoustic streaming.

An analytical theory is developed for acoustic streaming induced by an axisymmetric acoustic wave field around an isotropic solid spherical particle in a compressible viscoelastic fluid. The particle is assumed to undergo pulsation, translation, and shape deformations of all orders. The fluid motion is described by the compressible Oldroyd-B model.

Signatures of microstreaming patterns induced by non-spherically oscillating bubbles.

In this study, we report recent theoretical and experimental developments dealing with the axisymmetric flow surrounding non-spherically oscillating microbubbles. A wide variety of microstreaming patterns is revealed using a theoretical modeling providing exact analytical solutions of the second-order mean flows. The streaming pattern is highly dependent on the modal content of the bubble interface oscillation, including possibly spherical, translational, and nonspherical modes, as well as any combination of these modes.

Acoustic microstreaming produced by nonspherical oscillations of a gas bubble. IV. Case of modes n and m.

This paper is the conclusion of work done in our previous papers [A. A. Doinikov et al.

Acoustic Radiation Forces Produced by Sharp-Edge Structures in Microfluidic Systems.

We study sharp-edge structures that are used in microfluidic systems for particle and cell manipulation. Experiments show that oscillating sharp edges can attract or repel particles suspended in a microfluidic channel. This effect is caused by acoustic radiation forces induced by sharp edges.

Acoustic interaction between 3D-fabricated cubic bubbles.

Spherical bubbles are notoriously difficult to hold in specific arrangements in water and tend to dissolve over time. Here, using stereolithographic printing, we built an assembly of millimetric cubic frames overcoming these limitations. Indeed, each of these open frames holds an air bubble when immersed into water, resulting in bubbles that are stable for a long time and are still able to oscillate acoustically.

Acoustic microstreaming produced by nonspherical oscillations of a gas bubble. III. Case of self-interacting modes n-n.

This paper is the continuation of work done in our previous papers [A. A. Doinikov et al.

Acoustic streaming outside and inside a fluid particle undergoing monopole and dipole oscillations.

An analytical theory is developed for acoustic streaming induced by an acoustic wave field inside and outside a spherical fluid particle, which can be a liquid droplet or a gas bubble. The particle is assumed to undergo the monopole (pulsation) and the dipole (translation) oscillation modes. The dispersed phase and the carrier medium are considered to be immiscible, compressible, and viscous.

Acoustic microstreaming produced by nonspherical oscillations of a gas bubble. II. Case of modes 1 and m.

This paper continues a study that was started in our previous paper [A. A. Doinikov et al.

Acoustic microstreaming produced by nonspherical oscillations of a gas bubble. I. Case of modes 0 and m.

A theory is developed that allows one to model the velocity field of acoustic microstreaming produced by nonspherical oscillations of an acoustically driven gas bubble. It is assumed that some of the bubble oscillation modes are excited parametrically and hence can oscillate at frequencies different from the driving frequency. Analytical solutions are derived in terms of complex amplitudes of oscillation modes, which means that the mode amplitudes are assumed to be known and serve as input data when the velocity field of acoustic microstreaming is calculated.

Nonlinear dynamics of two coupled bubbles oscillating inside a liquid-filled cavity surrounded by an elastic medium.

A theory is developed to model the nonlinear dynamics of two coupled bubbles inside a spherical liquid-filled cavity surrounded by an elastic medium. The aim is to study how the conditions of full confinement affect the coupled oscillations of the bubbles. To make the problem amenable to analytical consideration, the bubbles are assumed to be located on a diameter of the cavity, which makes the problem axisymmetric.

Cavitation in a liquid-filled cavity surrounded by an elastic medium: Intercoupling of cavitation events in neighboring cavities.

The subject of the present theoretical study is the dynamics of a cavitation bubble in a spherical liquid-filled cavity surrounded by an infinite elastic solid. Two objectives are pursued. The first is to derive equations for the velocity and pressure fields throughout the liquid filling the cavity and equations for the stress and strain fields throughout the solid medium surrounding the cavity.

Model for the growth and the oscillation of a cavitation bubble in a spherical liquid-filled cavity enclosed in an elastic medium.

Equations are derived that describe the growth and subsequent damped oscillation of a cavitation bubble in a liquid-filled cavity surrounded by an elastic solid. It is assumed that the nucleation and the growth of the bubble are caused by an initial negative pressure in the cavity. The liquid is treated as viscous and compressible.

Acoustic streaming induced by two orthogonal ultrasound standing waves in a microfluidic channel.

A mathematical model is derived for acoustic streaming in a microfluidic channel confined between a solid wall and a rigid reflector. Acoustic streaming is produced by two orthogonal ultrasound standing waves of the same frequency that are created by two pairs of counter-propagating leaky surface waves induced in the solid wall. The magnitudes and phases of the standing waves are assumed to be different.

Acoustic streaming in a microfluidic channel with a reflector: Case of a standing wave generated by two counterpropagating leaky surface waves.

A theory is developed for the modeling of acoustic streaming in a microfluidic channel confined between an elastic solid wall and a rigid reflector. A situation is studied where the acoustic streaming is produced by two leaky surface waves that propagate towards each other in the solid wall and thus form a combined standing wave in the fluid. Full analytical solutions are found for both the linear acoustic field and the field of the acoustic streaming.

Radiation dynamics of a cavitation bubble in a liquid-filled cavity surrounded by an elastic solid.

A specific cavitation phenomenon occurs inside the stems of trees. The internal pressure in tree conduits can drop down to significant negative values, which causes the nucleation of bubbles. The bubbles exhibit high-frequency oscillations just after their nucleation.

Controlled rotation and translation of spherical particles or living cells by surface acoustic waves.

We show experimental evidence of the acoustically-assisted micromanipulation of small objects like solid particles or blood cells, combining rotation and translation, using high frequency surface acoustic waves. This was obtained from the leakage in a microfluidic channel of two standing waves arranged perpendicularly in a LiNbO piezoelectric substrate working at 36.3 MHz.

Acoustic streaming generated by two orthogonal standing waves propagating between two rigid walls.

An analytical solution is derived for the acoustic streaming generated by two orthogonal standing waves in a fluid confined between two plane rigid walls. It is assumed that the standing waves have the same frequency but, in general, are out of phase. The main restriction is that the boundary layer thickness is much smaller than the acoustic wavelength.

Impact of Filling Gas on Subharmonic Emissions of Phospholipid Ultrasound Contrast Agents.

Subharmonic signals backscattered from gas-filled lipid-shelled microbubbles have generated significant research interest because they can improve the detection and sensitivity of contrast-enhanced ultrasound imaging. However, the emission of subharmonic signals is strongly characterized by a temporal dependence, the origins of which have not been sufficiently elucidated. The features that influence subharmonic emissions need to be identified not only to better develop next-generation microbubble contrast agents, but also to develop more efficient subharmonic imaging (SHI) modes and therapeutic strategies.

Acoustic streaming produced by a cylindrical bubble undergoing volume and translational oscillations in a microfluidic channel.

A theoretical model is developed for acoustic streaming generated by a cylindrical bubble confined in a fluid channel between two planar elastic walls. The bubble is assumed to undergo volume and translational oscillations. The volume oscillation is caused by an imposed acoustic pressure field and generates the bulk scattered wave in the fluid gap and Lamb-type surface waves propagating along the fluid-wall interfaces.

Effect of surface waves on the secondary Bjerknes force experienced by bubbles in a microfluidic channel.

An analytical expression is derived for the secondary Bjerknes force experienced by two cylindrical bubbles in a microfluidic channel with planar elastic walls. The derived expression takes into account that the bubbles generate two types of scattered acoustic waves: bulk waves that propagate in the fluid gap with the speed of sound and Lamb-type surface waves that propagate at the fluid-wall interfaces with a much lower speed than that of the bulk waves. It is shown that the surface waves cause the bubbles to form a bound pair in which the equilibrium interbubble distance is determined by the wavelength of the surface waves, which is much smaller than the acoustic wavelength.

Experimental verification of theoretical equations for acoustic radiation force on compressible spherical particles in traveling waves.

Acoustophoresis uses acoustic radiation force to remotely manipulate particles suspended in a host fluid for many scientific, technological, and medical applications, such as acoustic levitation, acoustic coagulation, contrast ultrasound imaging, ultrasound-assisted drug delivery, etc. To estimate the magnitude of acoustic radiation forces, equations derived for an inviscid host fluid are commonly used. However, there are theoretical predictions that, in the case of a traveling wave, viscous effects can dramatically change the magnitude of acoustic radiation forces, which make the equations obtained for an inviscid host fluid invalid for proper estimation of acoustic radiation forces.

Lamb-type waves generated by a cylindrical bubble oscillating between two planar elastic walls.

The volume oscillation of a cylindrical bubble in a microfluidic channel with planar elastic walls is studied. Analytical solutions are found for the bulk scattered wave propagating in the fluid gap and the surface waves of Lamb-type propagating at the fluid-solid interfaces. This type of surface wave has not yet been described theoretically.