Flow Regimes Induced by Pulsating Gas Bubbles in Living Tissues
B.Krasovitski, E.Kimmel (Agricultural Engineering and Biomedical Engineering, Technion, Haifa, Israel)
Gas bubbles in living tissues, when subjected to therapeutic ultrasound (TUS), may be found in relatively large cavities such as blood vessels, in intercellular spaces and within cells. In the case of low intensity TUS, bubble close to a rigid wall in relatively large cavity undergoes steady pulsations. Laplace equation for potential flow is solved employing existing models for microstreaming and rectified diffusion to yield the steady shear stress on the surface. Significant values of localized shear are predicted when the distance of the bubble from the surface is comparable to bubble size. For greater TUS intensity, when bubble might collapse near a surface, we study bubble behavior in confined space that simulates a tiny cavity such as intercellular space. A numerical model is developed for a bubble in the middle of a liquid layer, between two rigid, parallel walls. The solution ia based on boundary integral method and consider surface tension effects. In some cases, the bubble divides into two symmetrical bubbles that collapse while high velocity jets are generated, aiming at the walls. The velocity of the jets strongly depends on the surface tension. Two new parameters define under what conditions the formation of jets is expected.
Section : 5