The veined wing of the clanger cicada kills bacteria solely through its physical structure — one of the first natural surfaces found to do so. An international team of biophysicists has now come up with a detailed model of how this defense works on the nanoscale. The results are published in the latest issue of the Biophysical Journal.

The clanger cicada (Psaltoda claripennis) is a locust-like insect whose wings are covered by a vast hexagonal array of 'nanopillars' — blunted spikes on a similar size scale to bacteria (see video, bottom). When a bacterium settles on the wing surface, its cellular membrane sticks to the surface of the nanopillars and stretches into the crevices between them, where it experiences the most strain. If the membrane is soft enough, it ruptures (see video, below).

Lead study author Elena Ivanova of Australia's Swinburne University of Technology in Hawthorne, Victoria, says that she was surprised that the bacterial cells are not actually punctured by the nanopillars. The rupturing effect is more like “the stretching of an elastic sheet of some kind, such as a latex glove. If you take hold of a piece of latex in both hands and slowly stretch it, it will become thinner at the center, [and] will begin to tear,” she explains.

To test their model, Ivanova and her team irradiated bacteria with microwaves to generate cells that had different levels of membrane rigidity. Their hypothesis was that the more rigid bacteria would be less likely to rupture between the nanopillars. The results validated the model, but also demonstrated that the cicada’s nanopillar defense is limited to bacteria that have sufficiently soft membranes.

Further study of the cicada’s wing is needed before its physical-defense properties can be mimicked in man-made materials. Anne-Marie Kietzig, a chemical engineer at McGill University in Montreal, Canada, who was not involved in the study, suggests that materials based on this model could one day be applied to public surfaces that commonly harbor disease, such as bus railings. “This would provide a passive bacteria-killing surface,” she says, adding that it “does not require active agents like detergents, which are often environmentally harmful”.

This article is reproduced with permission from the magazine Nature. The article was first published on March 3, 2013.

4 Comments

1. 1. drparent 12:52 PM 3/5/13

   '... materials based on this model could one day be applied to public surfaces that commonly harbor disease, such as bus railings. “This would provide a passive bacteria-killing surface,” she says, ...'
   
   Uh... If this surface destroys the cell membrane of bacteria, what would happen when I place my hand, constructed of cells, on that bus railing?! I hope the keratin layer of my epidermis is sturdy enough... Maybe we'll all just be well-exfoliated.

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2. 2. Xopher425 01:38 PM 3/5/13

   I would think that the cells in our epidermis would be a little tougher than that of a bacterial cell.
   
   I'm wondering if the nanopillars would be worn away from all of the contact, though.

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3. 3. gmperkins 04:35 PM 3/5/13

   I think dirt and such would keep subway railing use from happening. But I can imagine a number of interesting applications. And, when can I line my sinus membranes with this stuff? Haha, an unlikely use but I'll take what I can get during cold and flu season.

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4. 4. h1dden_blade 07:49 PM 3/6/13

   I think this would do well on a phone. we touch them a lot...

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