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Living creatures kill bacteria in many ways. We have our sophisticated immune system, and many moulds produce antibiotics. But a team led by Elena Ivanova of Swinburne University of Technology in Melbourne has discovered a unique way that the clanger cicada (Psaltoda claripennis) kills germs. This is purely by a physical structure, not through any chemical means. Since bacteria are microscopic, any physical structure that can kill them must be very tiny indeed.
The cicada's wings have a hexagonal array of nanopillars. These are only 200 nanometers high, 70 nm in diameter, and 170 nm apart (1 inch = 25.4 million nm). Thus even a bacterium is large on this scale, e.g. the pathogen Pseudomonas aeruginosa they tested is 1000–5,000 nm long and 500–1,000 nm wide.
The pillars surprisingly don't puncture the cell walls. Instead, they are attracted to the surface, and stretched into the crevices between them, until the wall bursts. Dr Ivanova explains that the mechanism 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 centre, [and] will begin to tear."
The team showed that the effect continued even when the surface was coated by gold, showing that there was no chemical on the wing that was killing the germs. Also, germs with more rigid cell walls were less susceptible, again supporting that the wing's structure worked by stretching past breaking point.
If this could be mimicked, it could provide a way of disinfecting surfaces that harbour germs, without using harmful chemicals.?
Biophysical model of bacterial cell interactions with nanopatterned cicada wing surfaces, Biophysical Journal 104(4):835–840, 19 February 2013.
Antibacterial surfaces: the quest for a new generation of biomaterials, Trends in Biotechnology 31, doi:10.1016/j.tibtech.2013.01.017, 20 February 2013.
Insect wings shred bacteria to pieces: Antibacterial 'nanopillars' on cicada wings pull bacterial membranes apart, NatureNews, 4 March 2013.