Modelling the microscopic mechanisms of sonoporation

Exposure of biological tissues to ultrasound waves above a threshold pressure amplitude can lead to permeabilization of the cell membrane and the unregulated uptake of exogenous species from the locale. This process is known as sonoporation. The approach appears to have significant potential for the non-invasive treatment of diseased and dysfunctional tissues. Interestingly, the extent of molecular uptake is noticeably enhanced when microscopic bubbles, usually in the form of commercial ultrasound contrast agents (UCA) are present during ultrasound exposure [insonation]. The physical mechanism leading to enhanced permeabilization had, until recently, remained elusive. It has emerged that the microbubbles effectively act as pre-nucleated cavitation centres and that their proximity to hydrodynamic constraints [nominally tissue planes] leads naturally to asymmetric collapse and the formation of microjets. For the purposes of the present paper, we show by comparison with in-house generated observations, that a computational model based on boundary element methods goes some way to simulating many of the salient aspects of cavitating microbubbles near boundaries, including microjetting.