Biofilms are colonies of bacteria that form on virtually any surface. They form on teeth, causing plaque and its related dental problems; they form on metal pipes, causing corrosion; and they form on medical implants causing infection and inflammation. They are very difficult to treat with liquid and gaseous biocides because the composition and structure of biofilms make them difficult to penetrate, keeping the subsurface bacteria safe. In fact, their surfaces repel certain liquids even better than anti-stick Teflon surfaces or lotus leaves. The surface of Teflon will appear wet when a 20% solution of ethyl alcohol in water is applied, while the surface of a Bacillus subtilis biofilm repels even an 80% alcohol solution. Even 50% solutions of other low surface tension biocides, such as acetone, methyl alcohol, and isopropyl alcohol, do not wet the surface of a B. subtilis biofilm. Bacterial biofilms achieve this function through the combined effects of chemical composition (biodegradeable polysachharides and proteins) and nano-scale roughness/topography of its surface.
"[T]he biofilm nonwetting properties arise from both the polysaccharide and protein components of the extracellular matrix and are a synergistic result of surface chemistry, multiscale surface roughness, and reentrant topography...because liquids and gases cannot fully penetrate into the matrix, [many of our most commonly used biocides] cannot access all the subsurface cells and are largely ineffective." (Epstein et al. 2010:998)
"To our knowledge, the extreme liquid repellency of B. subtilis biofilm has not been reported for any natural material...As a resilient, environmentally adaptive repellent surface composed of only nontoxic biomolecules, B. subtilis biofilm holds promise as a model surface that can open new directions in antiwetting applications.” (Epstein et al. 2010:999)