(182a) Vibration at Structural Resonance Frequency of Hydrophilic Substrates Enhances Biofilm Removal

Biological fouling caused by biofilms poses a grave concern for both human health and industrial infrastructure by causing infection, corrosion of metals, failure of medical and industrial equipment, and persistent drag on marine ships. External mechanical vibrations are commonly used to clean bio-fouled substrates. However, vibration conditions are often chosen without an in-depth understanding of structure-biofilm interactions. As such, this study interrogates the integrative effects of the surface energy of a substrate and vibration conditions including frequency and voltage-induced energy input mode on removing biofilms.

For this study, we assembled a polypropylene substrate coated with a polyacrylamide hydrogel that does not weaken during vibration and attached it to a dielectric elastomer that causes controlled, continuous deflection. The polyacrylamide gel was engineered to have a high surface energy of around 73.5 mN m^-1 and present a low number of hydrophobic crosslinks (i.e., 1:10800 molar crosslinker ratio). Both of which contribute to minimizing bacterial adhesion by reducing the number hydrophobic regions that cell-adhesive biomolecules can deposit. The tough gel coating was effective to lower the adhesion force of biofilms from 666 to 5.8 Pa (before and after coating) as measured by atomic force microscopy (AFM). Furthermore, the coated substrate could self-remove mature biofilms cultured up to 7 days when vibrated at the resonance frequency of the substrate. Using this set-up, we discovered that vibration at the structural resonance frequency using a square wave-form resulted in the highest deflection of the surface and maximizes the removal of biofilms. The findings from this study can be broadly applicable to the enhancement of various self-cleaning medical and industrial devices.