The left-right symmetrical and asymmetrical deformations in a three-bubble system

The oscillations of non-spherical bubbles in liquid

In this paper, the interaction between non-spherical bubbles is studied using a high-speed camera, and the effects of the interaction on the temperature within the bubble and the velocity of the surrounding fluid are theoretically investigated. It is found that the mean radius and the mean wall velocity of the middle bubble in three-bubble system are slightly greater than those in two-bubble system when the initial parameters are consistent. The acoustic response of the middle bubble presented a leftward shift of resonance peak and an increase of resonance peaks with increasing sound pressure. Two patterns of interactions were found in the three-bubble system: steady oscillations with slight non-spherical shape deformation, and a strong coupled state that tends to coalesce. In both patterns, the largest bubble should impose more constraints on the middle bubble, and the middle bubble was observed to be ejected towards the largest. The interacting pattern of bubbles depends on many factors, such as bubble spacing, initial radii of bubbles, acoustic frequency and intensity, which also affect the shape deformation of bubbles. Non-spherical shape deformation decreases the internal gas temperature and disturbs the flow field distribution, all of which are close to cavitation activities. Predictions of the three-bubble model are in good agreement with experimental observations, and can be used to explain bubble behaviors in chained multi-bubble systems in inertial cavitation field.

Numerical simulation study on opening blood-brain barrier by ultrasonic cavitation

Experimental studies have shown that ultrasonic cavitation can reversibly open the blood-brain barrier (BBB) to assist drug delivery. Nevertheless, the majority of the present study focused on experimental aspects of BBB opening. In this study, we developed a three-bubble-liquid-solid model to investigate the dynamic behavior of multiple bubbles within the blood vessels, and elucidate the physical mechanism of drug molecules through endothelial cells under ultrasonic cavitation excitation. The results showed that the large bubbles have a significant inhibitory effect on the movement of small bubbles, and the vibration morphology of intravascular microbubbles was affected by the acoustic parameters, microbubble size, and the distance between the microbubbles. The ultrasonic cavitation can significantly enhance the unidirectional flux of drug molecules, and the unidirectional flux growth rate of the wall can reach more than 5 %. Microjets and shock waves emitted from microbubbles generate different stress distribution patterns on the vascular wall, which in turn affects the pore size of the vessel wall and the permeability of drug molecules. The vibration morphology of microbubbles is related to the concentration, arrangement and scale of microbubbles, and the drug permeation impact can be enhanced by optimizing bubble size and acoustic parameters. The results offer an extensive depiction of the factors influencing the blood-brain barrier opening through ultrasonic cavitation, and the model may provide a potential technique to actively regulate the penetration capacity of drugs through endothelial layer of the neurovascular system by regulating BBB opening.

Dynamics of three cavitation bubbles with pulsation and symmetric deformation

A new system of dynamical equations was obtained by using the perturbation and potential flow theory to couple the pulsation and surface deformation of the second-order Legendre polynomials (P₂) of three bubbles in a line. The feasibility and effectiveness of the model were verified by simulating the radial oscillations, surface deformation with P₂, and shape evolution of three bubbles. The spherical radial pulsation and surface deformation of the three bubbles exhibit periodic behavior. The maximum secondary Bjerknes forces (SBFs) on the three bubbles are found not to depend on the system's resonance frequency. Within a stable region, the SBFs of the three bubbles increase with increasing sound pressure amplitude but decrease with increasing distance between the bubbles. The primary Bjerknes force (PBF) on a bubble is significantly higher than the SBF on it.