Comsol modelling of non-spherical microbubble dynamics near a soft membrane

A combination of ultrasonic irradiation and microbubble oscillations can increase the permeability of a cell membrane to increase uptake of a therapeutic agent. In the literature, non-spherical deformation near a boundary has been observed close to pressures triggering cavitation; often forming jets that may create localized cell membrane damage. This effect is one known to participate in the treatment of cancerous tumours with drug loaded microbubbles. In this study, a viscoelastic Finite Element Analysis (FEA) model for simulating the response of a phospholipid encapsulated microbubble to ultrasound in the vicinity of a soft membrane is described. It is the first model to use the generalized Maxwell model to simulate the viscous effect of the phospholipidic encapsulation of microbubbles in COMSOL Multiphysics^TM. The aim of the model is to study the non-spherical three dimensional deformations at high acoustical insonation pressures and investigate how the microbubble position and the pressure field affect the microbubble shape. To verify the validity of the model, the resonance frequencies obtained for a 2, 3 and 4 μm radii encapsulated microbubble have been compared with published experimental studies and their relative error were found to be within 12%. The results show a non-negligible effect from the reradiated pressure at high acoustical pressure involved in the formation of an inward protrusion opposite to the travelling direction of the ultrasound excitation.