Cinephotographic observations of particle removal from a surface by acoustic cavitation

It is commonly believed that ultrasonic cleaners remove particles from a surface through acoustic cavitation, presumably in which a pulsating bubble interacts directly with the particle. We are unaware of any direct evidence of this interaction. Recently, however, we have used a high‐speed movie camera to observe the removal of biofilm attached to a solid surface during exposure to a cavitation field. The biofilm consisted of Streptococcus mutans, a common oral bacterium, grown on a glass slide and observed under magnification to be both thinly coating the glass surface and clustered in larger colonies. The cavitation field was created by an UltreoTM toothbrush which combines both vibrating bristles and an ultrasound transducer with waveguide, operating at a frequency of 324 kHz. When the waveguide was immersed in water containing bubbles from an ultrasound contrast agent (OptisonTM), visual observations could be made with the naked eye of biofilm removal. With high‐speed cinephotography, it was possible ...