Air and Water Repellant Surface Prevents Entry of Fluids

close up photograph of bacteria in a petri dish

Biological Strategy

Bacteria

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Protect From Excess Liquids

While water is essential to life, too much water or other liquids can overwhelm living systems. Excess liquids can, for example, decrease a living system’s access to oxygen, promote excessive bacterial or fungal growth, or strip away soil and nutrients. To prevent the accumulation of excess liquids, living systems must control the movement of liquids across their boundaries or surfaces. They do so using waterproofing materials or structures, slowing flow, and/or facilitating flow to move the liquid away. Plant leaves, for example, commonly have waxy surfaces comprised of water-repelling chemicals to keep water from engorging the leaves or facilitating bacterial and fungal growth.

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Protect From Gases

Gases are part of most living systems’ environments, especially those exposed to the earth’s atmosphere. Two gases that can act as threats to living systems are oxygen and carbon dioxide; both, paradoxically, are also necessary to life. Thus, living systems must obtain a balance in gas concentrations, selectively protecting from too much gas in some situations and not enough in others. For example, mound-building termites protect themselves by building ventilation shafts to remove excess carbon dioxide from their fungal gardens.

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Prevent Deformation

When a living system undergoes compression, tension, shear, bending, or twisting, its internal inter-molecular forces can often resist these forces and even change shape temporarily, returning to the original shape when the forces stop. However, if the force is too strong or lasts too long, permanent deformation or structural failure can occur, resulting in death. Therefore, living systems have strategies to resist deformation or help ensure limited deformation. For example, bones have thin crystals and proteinaceous fibers that provide strength and flexibility, protecting them from forces that would otherwise cause deformation on a daily basis.

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Chemically Assemble Polymers

We might think that complex polymers are the result of human industrial ingenuity, but nature cornered the market on polymers billions of years earlier. Examples of biopolymers are proteins, carbohydrates, and genetic material. In contrast to human industrial processes, within a cell, ribosomes covalently bond amino acids together to form proteins.

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Bacteria

Domain Bacteria (“small staff”): L. acidophilus, Staphylococcus

From inside of our own bodies to the deepest parts of the ocean, bacteria have adapted to almost every possible environment. All bacteria are unicellular, microscopic, and lack a membrane-bound nucleus and organelles, and come in three basic shapes: spherical (cocci), rod (bacilli), and spiral (spirilla). Some strains can be deadly, like Staphylococcus aureus (MRSA) while others, like Lactobacillus acidophilus, found in our intestinal microbiome, keep us healthy. Cyanobacteria, also known as blue green algae, caused the Great Oxidation Event 2.4 billion years ago, producing Earth’s first oxygenated atmosphere.

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Biofilm colonies of Bacillus subtilis are highly water and gas repellant due to a combination of chemical composition and nano-scale topography.

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.

Last Updated November 16, 2016

References

Journal article

Bacterial biofilm shows persistent resistance to liquid wetting and gas penetration

Proceedings of the National Academy of Sciences | 30/12/2010 | A. K. Epstein, B. Pokroy, A. Seminara, J. Aizenberg

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