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Medical ultrasound technology is available, affordable, and non-invasive. It is used to detect, quantify, and heat tissue structures. This review article gives a concise overview of the types of behaviour that biological cells experience under the influence of ultrasound only, i.e., without the presence of microbubbles. The phenomena are discussed from a physics and engineering perspective. They include proliferation, translation, apoptosis, lysis, transient membrane permeation, and oscillation. The ultimate goal of cellular acoustics is the detection, quantification, manipulation and eradication of individual cells.

Recent in-vivo work showed the suitability of Pickering-stabilized antibubbles in harmonic imaging and ultrasound-guided drug delivery. To date, however, theoretical considerations of antibubble core properties and their effects on antibubble dynamics have been rather sparse. The purpose of this study was to investigate the influence of skeletal friction on the damping of a pulsating antibubble and the pulsation phase of an antibubble relative to the incident sound wave. Numerical simulations were performed to compute damping terms and pulsation phases of micron-sized antibubbles with thin elastic shells and 30% endoskeleton volume fraction. The simulations showed that the damping owing to skeleton presence dominates the damping mechanism for antibubbles of radii less than 2.5 μm, whilst it is negligible for greater radii. The pulsation phase of such small antibubbles was simulated to have a phase delay of up to 1/6 π with respect to pulsating free gas bubbles. Our findings demonstrate that the presence of an endoskeleton inside a bubble influences pulsation phase and damping of small antibubbles. Antibubbles of radii less than 3 μm are of interest for the use as ultrasound contrast agents.

This study explores the rigidity of Pickering-stabilised microbubbles subjected to low-amplitude ultrasound. Such microbubbles might be suitable ultrasound contrast agents. Using an adapted Rayleigh-Plesset equation, we modelled the dynamics of microbubbles with a 7.6-N m−1 shell stiffness under 1-MHz, 0.2-MPa sonication. Such dynamics were observed experimentally, too, using high-speed photography. The maximum expansions were agreeing with those predicted for Pickering-stabilised microbubbles. Subjecting microbubbles to multiple time- delayed pulses yielded the same result. We conclude that Pickering-stabilised microbubbles remain very stable at low acoustic amplitudes.

Pickering stabilisation is a manufacturing process involving the adsorption of colloidal particles at gas-liquid interfaces. It is used to create the shells of stable, long-lived ultrasound contrast agent microbubbles. The purpose of the present study is to determine whether high-amplitude sonication influences the integrity of Pickering-stabilised shells. To this purpose, Pickering-stabilised microbubbles were subjected to high-speed photography at 10 million frames per second during 1-MHz, 1-MPa sonication. In addition, radial excursions as a function of time were simulated using the Rayleigh-Plesset equation for free gas microbubbles and microbubbles encapsulated by Pickering-stabilised shells of 7.6-Nm−1 stiffness. The maximum expansions observed from camera recordings were either agreeing with those computed for Pickering-stabilised microbubbles or corresponding to greater values. The results indicate that optically identical microbubbles may undergo shell disruption of different severity. We conclude that the disruption occurs during sonication and not prior to it. These findings may aid in the development of Pickering-stabilised agents that facilitate ultrasoundtriggered release.

Controlled tablet disintegration is useful for chemical consistency checks. This study monitored the swelling of 54 analgesia tablets from two different batches, during 13–6-MHz brightness-mode sonication and simultaneous video recording. The tablets were placed on an acoustic reflector inside a container and sonicated from the top. Sonication shortened the displacement half-life by 17%–27%. During tablet swelling, their speed of sound increased linearly, confirming the linearity of the this process. Diagnostic ultrasound significantly decreased tablet disintegration times, supporting the ultrasound–microbubble interaction hypothesis.

Recently, the first high-speed video of a fragmenting antibubble was published. Nonetheless, this fragmentation process was not fully understood.Owing to a recent study on fragmenting glass, we can now conclude that an antibubble under tensile stress undergoes an exponential fragmentation process. This note gives a brief theoretical explanation and the first experimental data of a fragmenting antibubble. This is a highly relevant finding, as the fragmentation predictability of acoustically active antibubbles is required for their potential use in ultrasound-guided drug delivery.

For paper manufacturing and biofuel production, the controlled deformation of wood pulp is of interest, provided that the integrity of the fibre structure remains intact. Conventional ultrasonic pretreatment in the near-audible range has been observed to cause uncontrolled inertial cavitation damage in the wood pulp fibres. To prevent internal damage, we proposed to subject wood pulp mixed with hydrophobic particles to 1-MHz short pulses above the nucleation threshold of the particles but below the Blake threshold, and to observe the interaction of pulsating cavities and wood pulp fibres assisted by high-speed photography. Our 1-MHz results showed the interaction of a collapsing bubble with a wood pulp fibre wall to form a liquid jet hitting the fibre, without apparent destruction of the structure, whilst our 20-kHz controls confirmed previously observed structural destruction. This study shows the feasibility of controlled wood fibre deformation at a high ultrasound frequency.