The role of non-acoustic factors in the induction and proliferation of cavitational activity in vitro.

It is well known that a liquid exposed to relatively low intensities of MHz ultrasound may or may not cavitate depending upon a variety of non-acoustic factors. This paper shows that in some cases the material used as the acoustically transparent window and even the length of the sample chamber may also be important factors. Cling film, dialysis membrane and Parafilm are all equally acceptable as acoustically transparent windows for ultrasound, whereas glass cover slips or 'soft' surfaces (in which active bubbles may embed themselves) are not. All the results obtained confirm the validity of bubble recycling as being the dominant mechanism responsible for the enhancement of cavitational activity commonly observed when the sample chamber is rotated.