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Passive anti-bacterial materials

Looking to nature for some materials ideas is often a great source of inspiration. Tiny spikes on materials slowly deflate bacteria cells like balloons, killing the bacteria without any added chemicals or coatings.

The clanger cicada is a locust-like insect that can destroy bacteria using the material structure of its wing surface alone. Investigating the cicada’s wing surface reveals a fascinating principle and an opportunity for designers and inventors to revolutionise the anti-bacterial properties of surfaces such as hand rails, counter tops and doorknobs that are known to foster the spread of disease, particularly in the public realm.

The surface of the cicada’s wing is covered with ‘nanopillars’, which resemble blunt spikes. The cellular membrane of bacteria sticks to the surface of the nanopillars and stretches between the spikes, wherever it is under the most strain. Bacteria cells are not punctured immediately by the nanopillars but stretched until the cells thin and begin to tear and rupture, thus killing the bacteria. This is a bit like a water balloon landing on a bed of blunt nails. While the nails aren’t sharp enough to puncture the skin of a water balloon, the weight of the water pushes on the skin of the balloon between the spikes, causing the skin to stretch and ultimately deflate or rupture.

Further study will be required before these material properties can be reproduced in a man-made material. But the great thing is that nature offers us a passive, organic, bacteria-killing surface that doesn’t rely on harsh agents or detergents, which could potentially be environmentally damaging. Another advantage is the physical longevity of the material. The cicada’s wings gain their anti-bacterial qualities from the unalterable shape and form of their surface, rather than from active agents present in industry standard anti-bacterial coatings and surfaces.

For our exhibition on The Healing Environment, we’re looking at innovative materials that can really make a difference to the way that the built environment helps us get – and stay – healthy. Anti-bacterial coatings work well but often damage the material itself, are detrimental to the environment, or last for limited periods of time. The cicada principle could lead to all sorts of exciting, safe, anti-bacterial materials.

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