Taking their inspiration from the bombardier beetle, researchers have developed a film that they say could be used to coat ATMs, spraying would-be thieves and vandals with a hot foam.
The centimetre-long bombardier beetle possesses what is "surely the most aggressive chemical defence system in nature," claim a team from ETH Zurich University
When threatened, the beetle mixes two separately stored chemicals in a reaction chamber in its abdomen. An explosion is triggered with the help of catalytic enzymes and a caustic spray, accompanied by a popping sound, is released.
Inspired, the researchers developed a chemical defence mechanism designed to prevent vandalism - a self-defending surface composed of several sandwich-like layers of plastic. If the surface is damaged, hot foam is sprayed in the face of the attacker.
The layers are plastic films with a honeycomb structure. The hollow spaces are filled with either hydrogen peroxide or manganese dioxide. When the layers are destroyed by impact, a violent reaction is triggered, producing water vapour, oxygen and heat.Images showing foam released from the film
The university team suggest that an ideal use for their product is the protection of ATM cash boxes. And by adding a dye to the mix, thieves would not only get a nasty spray but the bank notes would be rendered worthless. A EUR5 note dyed by the self-defending surface
Wendelin Jan Stark, professor, ETH Department of Chemistry and Applied Biosciences, says: "When you see how elegantly nature solves problems, you realise how deadlocked the world of technology often is."
Back in 2009, South African bank Absa sought to deter criminals from bombing its ATMs by fitting them with pepper spray but the plan backfired when a rogue machine attacked maintenance workers.