Cavitation dosimetry: estimates for single bubbles in a rotating-tube exposure system

Cell lysis and hydrogen peroxide production from cavitation in a 60 rpm rotating-tube exposure system were observed for 2.17 MHz ultrasound at 0.8 MPa peak negative pressure amplitude. Synchronized 10 ms burst mode exposure was utilized to emphasize the phenomenon of bubble cycling each half rotation. Low cell numbers and inhibition of H2O2-consuming enzymes allowed measurement of the residual hydrogen peroxide in exposed cell suspensions. Canine red blood cells (RBCs) or Chinese hamster ovary cells (CHO) suspended at 1 x 10(6) mL-1 in phosphate buffered saline were lysed exponentially with the number of bursts. The CHO cells were lysed faster than RBCs. The H2O2 increased approximately in proportion to the number of bursts. Longer bursts (100 ms) or continuous exposure produced similar trends, but were less effective per unit of total on-time. The number of bubbles per 10 ms burst was estimated from a simple model to be about 7100. The faster lysis of the CHO cells could be explained mostly by the larger size of these cells, which makes them more likely to meet a bubble. The H2O2 production gave concentrations of about 93-155 fM per bubble per burst. Similar calculations gave estimates of 178 fM per bubble for 100 ms bursts and 150 fM per bubble for continuous exposure. The rate of H2O2 production was roughly 500 fmole s-1 while a bubble crossed the tube. This sonochemical yield could be biologically significant under favorable circumstances.