Erosion of artificial endothelia in vitro by pulsed ultrasound: acoustic pressure, frequency, membrane orientation and microbubble contrast agent dependence

The erosion of cells from fibroblast monolayers simulating the vascular endothelium by 20 micros pulses of ultrasound at 500 Hz PRF was studied in relation to the peak negative acoustic pressure (P-; 0.0-2.5 MPa), ultrasound (US) frequency (1.0, 2.1 or 3.5 MHz), orientation of the monolayer (i.e., simulating the sites of ultrasound entry/exit from a blood vessel) and the presence or absence of a microbubble contrast agent (3 Vol% Albunex). The a priori hypotheses were that erosion of the monolayers would: 1. arise due to insonation treatment, 2. arise as a consequence of cavitation activity and, thus, increase with increasing P- at constant frequency, and decrease with increasing frequency at constant P-, 3. be significantly increased by the presence of a microbubble contrast agent, and 4. have a weak dependence on monolayer orientation. The data support these hypotheses. Under the most severe exposure conditions used, most of the affected cells appeared to have been lysed; however, a substantial number of viable cells were dislodged from the monolayer surface.