Cell death in the thin films of bursting bubbles.

A sparged gas bubble floating at the liquid interface has a liquid film which drains and thins until the film spontaneously ruptures at a point. This causes rapid retraction of the film, forming a rim of collected fluid. This rim moves at a constant velocity of about 3 m/s and any cells in the bubble film are rapidly accelerated to this velocity in the moving rim. Half of the surface energy originally in the thin film is converted to kinetic energy of the rim, while the rest is dissipated in this rim. The rate of energy dissipation per mass of rim fluid is approximately 9000 m2/s3, which corresponds to a Kolmogorov eddy size of 3.2 microns in fully developed turbulence or a shear stress of 95 N/m2 in laminar flow. Either of these limiting cases presents an environment in which rapid cell death would be expected. Experiments with Sf-9 insect cells suggest that the cell concentration in these thin films is 0.6 times the bulk liquid concentration and that about 20% of these cells are killed when the film ruptures. An equation based on this mechanism accurately predicts the death rate.