Physical and Chemical Aspects of Ultrasonic Disruption of Cells

An assessment is made of the relative contributions of mechanical and sonochemical effects to damage suffered by mammalian cells when sonicated in aqueous-suspension culture. In a 1-MHz progressive wave beam, under conditions providing stabilization of the cavitation field, the intensity threshold and intensity optimum for cell disintegration occur at about 1 and 5 W cm−2, respectively, and the same pattern is found for the liberation of free iodine in solutions of KI. The cell culture medium is, however, found to have a chemiprotective effect on the cells, probably as a result of successful competition for OH radicals on the part of glucose and amino acid constituents of the medium. Thus, although prolonged sonication of the medium can eventually reduce its ability to support cells, such indirect effect is insignificant the relatively short irradiation times required to kill 99% of cells and the primary mechanism of damage here appears to be mechanical. Pulsing conditions have an important influence on both cell disintegration and iodine-release rates, which both show maxima for 30-msec pulse duration and drop to zero for pulse durations below 1 msec. The relevance of this finding to the kinetics of cavitation mechanisms discussed.