Bacteria in biofilms adhere well to surfaces and are quite difficult to remove. Oral plaque is one example of a biofilm. Many researchers have studied ways to remove plaque and bacteria from surfaces. It has been found that the passage of a bubble across a surface to which bacteria has adhered can remove the bacteria from the surface. Biofilms of Streptococcus mutans were grown on glass coverslips as a simple model for oral plaque. The coverslips were mounted in a Plexiglas chamber filled with artificial saliva. A bubble stream was directed at the mounted biofilm. The velocity, gas fraction, median bubble diameter, and impingement angle were all varied to determine the effect of each parameter on removal and which parameter was the most significant. To investigate the influence of sound on removal, a Ling oscillator was attached to the chamber, and was used simultaneously with and without a bubble stream. The acoustic intensity and the frequency were varied to determine if there was any effect on biofilm removal. Biofilm removal was also video taped. The results of these experiments confirmed that biofilms are removed by a stream of bubbles. Removal of biofilm is a function of stream velocity, gas fraction, and median bubble diameter, but not of impingement angle. The results of the acoustic experiments show that sound does not affect the removal of biofilm under the conditions used in these experiments. Mathematical models relating the removal of biofilm as a function of time were also developed from the data obtained from the video recording of the experiments. Additional tests using acoustic waves to remove biofilm should be performed to determine if more intense sound can remove biofilm. The intensity of the sound used in these experiments was low and the time of exposure was only 5 sec. Additional tests that more closely simulate the conditions of the mouth during brushing, like adding a surfactant, would also provide more insight as to whether bubbles in a clinical setting would remove biofilm.



College and Department

Ira A. Fulton College of Engineering and Technology; Chemical Engineering



Date Submitted


Document Type





biofilm, bacteria, Streptococcus mutans, bubbles, sound, acoustic waves, angle