Institute of Fundamental Technological Research

Manipulating particles in the blood pool with noninvasive methods has been of great interest in therapeutic delivery. Recently, it was demonstrated experimentally that red blood cells can be forced to translate and accumulate in an ultrasound field. This acoustic response of the red blood cells has been attributed to sonophores, gas pockets that are formed under the influence of a sound field in the inner-membrane leaflets of biological cells. In this paper, we propose a simpler model: that of the compressible membrane. We derive the spatio-temporal cel dynamics for a spherically symmetric single cell, whilst regarding the cell bilayer membrane as two monolayer Newtonian viscous liquids, separated by a thin gas void. When applying the newly-derived equations to a red blood cell, it is observed that the void inside the bilayer expands to multiples of its original thickness, even at clinically safe acoustic pressure amplitudes. For causing permanent cell rupture during expansion, however, the acoustic pressure amplitudes needed would have to surpass the inertial cavitation threshold by a factor 10. Given the incompressibility of the inner monolayer, the radial oscillations of a cell are governed by the same set of equations as those of a forced antibubble. Evidently, these equations must hold for liposomes under sonication, as well.

spatio-temporal cell dynamics, Rayleigh-Plesset equation, spherical cell, red blood cell, erythrocyte

Antibubbles are gas bubbles containing a liquid droplet core and, typically, a stabilising outer shell. It has been hypothesised that acoustically driven antibubbles can be used for active leakage detection from subsea production facilities. This paper treats the dynamics of spherically symmetric microscopic antibubbles, building on existing models of bubble dynamics. A more complete understanding of microbubble dynamics demands that the effects of the translational dynamics is included into the Rayleigh-Plesset equation, which has been the primary aim of this paper. Moreover, it is a goal of this paper to derive a theory that is not based on ad-hoc parameters due to the presence of a shell, but rather on material properties. To achieve a coupled set of differential equations describing the radial and translational dynamics of an antibubble, in this paper Lagrangian formalism is used, where a Rayleigh-Plesset-like equation allows for the shell to be modelled from first principles. Two shell models are adopted; one for a Newtonian fluid shell, and the other for a Maxwell fluid shell. In addition, a zero-thickness approximation of the encapsulation is presented for both models. The Newtonian fluid shell can be considered as a special case of the Maxwell fluid shell. The equations have been linearised and the natural and damped resonance frequencies have been presented for both shell models.

microbubbles, spatio–temporal bubble dynamics, Rayleigh-Plesset equation

In this study, we analyse the behaviour of antibubbles when subjected to an ultrasonic pulse. Speci cally, we derive oscillating behaviour of acoustic antibubbles with a negligible outer shell, resulting in a Rayleigh Plesset equation of antibubble dynamics. Furthermore, we compare theoretical behaviour of antibubbles to behaviour of regular gas bubbles. We conclude that antibubbles and regular bubbles respond to an acoustic wave in a very similar manner if the antibubble's liquid core radius is less than half the antibubble radius. For larger cores, antibubbles demonstrate highly harmonic behaviour, which would make them suitable vehicles in ultrasonic imaging and ultrasound-guided drug delivery.

An antibubble consists of a liquid droplet, surrounded by a gas, often with an encapsulating shell. Antibubbles of microscopic sizes suspended in fluids are acoustically active in the ultrasonic range. In this study, a Rayleigh-Plesset-like model is derived for micron-sized antibubbles encapsulated by Newtonian fluids. The theoretical behaviour of an encapsulated antibubble is compared to that of an antibubble without an encapsulating shell, a free gas bubble, and an encapsulated gas bubble. Antibubbles, with droplet core sizes in the range of 60– 90% of the equilibrium antibubble inner radius were studied. Acoustic pressures of 100kPa and 300kPa were studied. The antibubble resonance frequency, the phase difference of the radial oscillations with respect to the incident acoustic pulse, and the presence of higher harmonics are strongly dependent of the core droplet size. The contribution to the radial dynamics from a zero-thickness shell is negligible for the bubble size studied, at high acoustic amplitudes, antibubbles oscillate highly nonlinearly independent of core droplet size. This may allow for active leakage detection using harmonic imaging methods.

Active leakage detection, Antibubble, Bubble resonance, Microbubble, Nonlinear dynamics

An antibubble consists of a liquid droplet, surrounded by a gas, often with an encapsulating shell. Antibubbles of microscopic sizes suspended in fluids are acoustically active in the ultrasonic range. Antibubbles have applications in food processing and guided drug delivery. We study the sound generated from antibubbles, with droplet core sizes in the range of 0–90% of the equilibrium antibubble inner radius. The antibubble resonance frequency, the phase difference of the echo with respect to the incident acoustic pulse, and the presence of higher harmonics are strongly dependent of the core droplet size. Antibubbles oscillate highly nonlinearly around resonance size. This may allow for using antibubbles in clinical diagnostic imaging and targeted drug delivery.

Antibubble, Nonlinear, Echo, Rayleigh-Plesset, Targeted drug delivery

Hydroelectric power is a clean source of energy, providing up to 20% of the World's electricity. Nevertheless, hydroelectric power plants are plagued with a common problem: silt. The silt causes damage to turbine blades, which then require repairing or replacing. In this study, we investigated the possibility to filter micron-sized particles from water using ultrasound. We designed a custom-made flow chamber and performed flow simulations and experiments to evaluate its efficacy. We used a 195-kHz ultrasound transducer operating in continuous-wave mode with acoustic output powers up to 12W. Our acoustic simulations showed that it should be possible to force a 200-μm particle over 2cm in flow, using an acoustic pressure of 12 MPa. Our flow simulations showed, that the fluid flow is not drastically decreased with the flow chamber, which was validated by the experimental measurements. The flow was not reduced when the ultrasound was activated. The acoustic filtering was effective between acoustic powers of 2.6 and 6.4W, where the particle concentration in the clean output was statistically significantly lower than the null experiments.

Acoustic filtering

We study the sonication of stable particles that encapsulate a liquid core, so-called antibubbles. Acoustically active antibubbles can potentially be used for ultrasound-guided drug delivery. In this presentation, we derive the oscillating behaviour of acoustic antibubbles with a negligible outer shell, resulting in a Rayleigh-Plesset equation of antibubble dynamics. Furthermore, we compare the theoretical behaviour of antibubbles to that of regular gas bubbles. We conclude that antibubbles and regular bubbles are acoustically active in a very similar way, if the liquid core is less than half the antibubble radius. For larger cores, antibubbles demonstrate highly harmonic behaviour, which would make them suitable vehicles in ultrasonic imaging and ultrasound-guided drug delivery.

Harmonics, Antibubbles

Bubbles are emptiness, microscopic clouds surrounded by the world. Born by chance with a violent and brief life, collapsing in a union with the infinite [1]. Remarkably similar to the life of a human being. However, there are some discrepancies when comparing the life of a bubble, and that of a human being. For example, the nature of the acoustically active bubble is described by the language of mathematics, where understanding the behaviour of bubble dynamics has been a goal for physicists for centuries [2]. However, not only physicists have been enchanted by the intrinsic beauty encompassed in the simplicity of a bubble. Throughout history bubbles have been a symbol in art.

Antibubbles