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How Insect Wings Destroy Bacteria

In a new study, researchers describe how the veined wing of the Clanger cicada is the first known example of a natural biomaterial that kills bacteria on contact, using only its physical structure, unaided by chemical or biological agents. Tiny nanopatterns on the locust-like insect's wing surface simply tear the microorganisms apart. By studying such physical properties researchers hope to spur the design of new antibacterial materials that can be used on handrails and similar frequently-touched surfaces.

The international team of biophysicists report how they produced a detailed model of the biomaterial's nanoscale properties in the Biophysical Journal, a before print issue of which was published online on 19 February.

Lead author Elena Ivanova of Australia's Swinburne University of Technology in Hawthorne, Victoria, and colleagues suggest their "findings demonstrate the potential benefits of incorporating cicada wing nanopatterns into the design of antibacterial nanomaterials".

The manipulation of matter at the atomic and molecular scale to create materials with remarkably varied and new properties, nanotechnology is a rapidly expanding area of research.

The scale of nanotechnology is the nanometer (nm), which is one billionth of a meter, or 0.000000001 meters. A nanometer is about three to five atoms wide and about 40,000 times thinner than a human hair.

The wings of the Clanger cicada (Psaltoda claripennis) are covered by nano-sized "pillars" arranged in a vast hexagonal pattern. At the scale of bacteria, they look like blunt spikes.

When a bacterium lands on the wing surface, the membrane that surrounds the one-celled microorganism sticks to the surface of the nano-sized pillars, whereupon it begins to stretch into the crevices between them. Here, the bacterium's membrane is under a lot of strain, and if it is soft enough, it will tear.

Ivanova and colleagues experimented with bacteria with different physical properties to see what happens when they land on the wing surface. They found the ones with the most rigid membranes were the ones least likely to rupture on the nanopillars on the wings.

They experimented further by exposing the more rigid bacteria to microwaves to soften their membranes, and showed if they were soft enough, the nano-pillars killed them.

The researchers say they need to find out more about the cicada's wing properties before they can try to make an artificial version of the nanopattern material, however, the results of their study are enough to put forward:

"... a biophysical model of the interactions between bacterial cells and cicada wing surface structures, and show that mechanical properties, in particular cell rigidity, are key factors in determining bacterial resistance/sensitivity to the bactericidal nature of the wing surface".

Anne-Marie Kietzig, a chemical engineer at McGill University in Montreal, Canada, was not involved in the study. She says in a report by Nature NEWS that the model Ivanova and colleagues are developing could one day help make bus-railings and other frequently-touched surfaces commonly found in public places. These often harbour disease-causing bacteria.

An obvious benefit of such a material is that it would "not require active agents like detergents, which are often environmentally harmful," she adds.

In a March 2012 issue of Nano Letters, researchers at Massachusetts Institute of Technology (MIT) describe how they designed nanoparticles that produce proteins when utraviolet (UV) light shines on them: they suggest the idea could be used to create "nano-factories" that make protein-based drugs at tumor sites to fight cancer.

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