We investigated the viability of vascular endothelial cells with the existence of lipid bubbles under ultrasound exposure. First, we estimated the various situations of bubbles on the cells including either adhesion, floating, or both of them using not only image analysis but also an experiment to retain the cells in flow. Then we examined the viability measurement of the cells using the ultrasound conditions with the frequency of 3 MHz, a maximum sound pressure of 400 kPa-pp, and a maximum irradiation time of 60 s. We found that the floating bubbles caused more damage on the cells rather than the adhered bubbles. Because insufficient adhesion of bubbles might cause damage by floating bubbles, we consider that the adhered bubbles were protective of cells against floating bubbles. However, excessive bubbles with a higher concentration than the saturation also might cause damage by destructing both of floating and adhered bubbles.

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