Probing the bioeffects of cavitation at the single-cell level

Abstract

Cavitation induced bioeffects has not been resolved satisfactorily due to the randomness in the inception and bubble dynamics produced by ultrasound. We have developed a microfluidic system to observe consistently the interaction of laser-generated tandem bubbles (50 μm in diameter) with resultant jet formation, cell deformation, and localized membrane rupture with progressive diffusion of propodium iodide (PI) into individual HeLa cells placed nearby. We observe a clear stand-off distance (SD) dependence in the bioeffects produced by the tandem bubbles. At SD of 10 μm, all cells underwent necrosis with high, unsaturated level of PI uptake. At SD of 20~30 μm, 58 to 80% of the cells showed repairable membrane poration with low to medium but saturated level of PI uptake. Within this range, the sub-population of cells that survived without apoptosis increased from ~9% at SD of 20 μm to ~70% at SD of 30 μm. The maximum PI uptake, pore size, and estimated membrane strain, however, could vary by more than an order of magnitude at each SD. At SD of 40 μm, no detectable PI uptake was observed. This experimental system provides a unique tool to probe the bioeffects of cavitation at the single cell level.