Behavior of Phospholipid Layer-Coated Microbubbles under Pressure Change

Abstract

The shrinking and growth of microbubbles under pressure change are observed with a CCD camera. The influence of gas diffusion on the stability of microbubbles coated by phospholipid is investigated. The microbubbles are made with acoustic liposomes encapsulating phosphate buffer solution and perfluoropropane gas. It is shown that when the ambient liquid pressure increases, the observed microbubbles shrink accompanied with the cyclic surface deforming and smoothing process. The bubble surface smoothing shows that the excess phospholipid layers are removed from the surface, which results in the instantaneous bubble shrinkage. It is also shown that the smaller the initial radius is, the more the growth of microbubbles is reduced. The experiments are compared with the simulations in which the dynamic surface tension and the variation of gas permeation resistance of molecular layers are taken into account. The instantaneous bubble shrinkage in the experiment is simulated successfully with the bubble model in which the instantaneous increase of surface tension due to the reduction of the excess phospholipid layer material is taken into account.