Dynamics and fragmentation of encapsulated gas bubbles

The development of ultrasound contrast agents has fostered an interest in the theoretical dynamics of encapsulated gas bubbles. Originally, micron‐sized agents were constructed for diagnostic imaging purposes with a thin shell (<15 nm) of lipid, protein, or polymeric materials. New therapeutic applications for localized drug delivery have led to an interest and development of micron‐size bubbles with a thick fluid shell (∼500 nm). Previously some experimental acoustic levitation studies have investigated the capillary wave development on millimeter‐size liquid shells. The nonlinear oscillations and fragmentation have not been extensively investigated from the theoretical standpoints. A generalized Rayleigh–Plesset equation has been developed that includes the effects of a thick viscous fluid shell. The equation is compared with other theoretical encapsulated bubble formulations and some recent experimental observations. For a 4.0 μ bubble, with a 500 nm shell of viscosity of 28 cP, insonified over 5 cycle...