The Gecko’s Foot: How Scientists are Taking a Leaf from Nature's Book. Peter Forbes

phenomenon itself was not known until discovered by the technologists! Obvious examples are echo-location in bats and sonar in whales and dolphins: before ultrasound was invented scientists could have dissected bats for eternity and still not understood their echo-location mechanism.

      The most dramatic recent example has been the photonic crystal: a nanostructured crystal that will enable light to be guided at fantastic speeds through the crystal to create pathways in which information can be stored and manipulated. The photonic crystal was predicted as a theoretical possibility by physicists in 1987, first created technically in 1991, and discovered in butterflies and marine creatures in the late 1990s. In other areas, biological discovery has led to technical invention in the true spirit of bio-inspiration. In fact, in the case of the Lotus-Effect, once the biological effect was established – that some plant leaves have a micro-structure that produces highly developed water repellency and self-cleaning – it was realized that physicists had produced a general theory to account for this 50 years earlier, but its importance had not been recognized. Now, super-water repellency is a respectable subject in many physics and materials science laboratories where you won’t find a leaf of any kind.

      Bio-inspiration is not a narrow discipline. Origami was once thought merely to be an amusing game, nothing to do with science. Then mathematicians realized that it could be interesting to them, as a branch of topology: the maths of shapes. Origami is used by nature because some structures such as leaves and wings need to be folded. Now whenever human engineers want to deploy structures (erect something that is usually kept folded), they look at the ways nature uses origami.

      Although Primo Levi, the great Italian writer and chemist who died in 1987, did not live long enough to see the birth of bio-inspiration, he did have an abiding interest in the natural world. He was especially fascinated by insects and in his essays (Other People’s Trades) he said of beetles:

      These small flying fortresses, these portentous little machines, whose instincts were programmed one hundred million years ago, have nothing at all to do with us, they represent a totally different solution to the survival problem.

      But beetles, like every other major group in the natural world, do have something to offer us. The flashing light of the firefly (a beetle despite the name) is caused by a chemical reaction that produces almost no heat and this has been mimicked to produce biomedical diagnostic tests. The Oxford zoologist Andrew Parker has discovered a desert beetle that has a novel way of capturing the sparse water that comes its way and this too will have technical applications.

      And what of the bombardier beetle, a creature that seems to have anticipated many of the principles of human rocketry? It has a powerful defence mechanism that involves directing a hot irritant spray in the direction of an attacker. The chemical propellant for the spray turns out to be hydrogen peroxide, a well-known human rocket fuel. The peroxide is mixed with hydroquinones in a ‘reaction chamber’; the reaction is hot (80°C) and the gases produced result in an explosive exhaust. The reaction chamber can be swivelled like a rocket motor to point towards the attacker. The whole business sounds far more like human technology than a natural creature. The more we know about beetles the more they seem to be little compendia of bio-inspirational properties.

      Bio-inspiration can work across the whole size spectrum but there is no doubt that most of the work presently being carried out is in the former Blind Zone, the nanoregion. The idea that the properties of things as experienced by us derive from tiny structures goes back a very long way: back to the 5th-century-BC Greek philosophers Democritus and Leucippus who proposed the atomic theory of matter. Their ideas are known to us through the exuberant epic poem De Rerum Natura by the Roman poet Lucretius (c. 100–c. 55 BC). Lucretius would have loved bio-inspiration. He tried to answer fundamental questions: What is the world made of? Can matter be created or destroyed? Are conscious beings made of conscious stuff? How does life renew itself? And despite three centuries of modern science that would have astonished Lucretius, many everyday things remained unexplained until recently. As he makes clear in De Rerum Natura, he was aware of the mystery of nature’s tiny functioning organs:

      How small can anything be? We know of creatures

      So tiny they would seem to disappear

      If they were less than half their present size.

      How big do you suppose their livers are?

      Their hearts? The pupils of their eyes? Their toes?

      Pretty minute you must admit.

      Lucretius believed that the underlying particles of the material world could not have the same properties that appear to our eyes. They had to be colourless, odourless and tasteless (and lacking consciousness). It was a subtle idea; you might think that if you kept chopping something up until it was very small it would be the same all the way through – just smaller – but it was Lucretius’s intuition (I refer to this as the Lucretian Leap) that, at the smallest scale, things just had to be different. In this sense, Lucretius and his forebears were the first nanotechnologists, although the subject had only a notional existence in their imaginations.

      De Rerum Natura gives us, in a language all can understand, a passionate explanation of the way things are. Indeed, it is unfortunate that modern science has not proved amenable to the Lucretian treatment. But bio-inspiration is remarkably Lucretian in spirit. It answers simple bold questions about aspects of nature: Why is the lotus leaf always clean? How does the gecko walk upside down? How can a spider’s web be stronger than steel? How can a fly of little brain be more manoeuvrable than a Eurofighter?

      The answers to these questions are also Lucretian. Lucretius constantly argues that the causes of the effects that we see are different in kind to the effects. This could almost be the first law of bio-inspiration: the tidiest surfaces are the roughest at the nanolevel; the structures that cause the colour of the peacock’s tail are not coloured; the hairs on the feet of the gecko are not sticky.

      Take silk, a byword for slinkiness. But what is the gorgeous crackle it makes when you rub it against itself (known as ‘scrooping’) and what causes the colour changes when dyed silks are viewed from different angles? Early synthetic silks did not have these properties because the fibres were smooth and of rounded section. But under the SEM a natural silk fibre will be observed to have micro-structured rough edges – not at all what might be expected from the feel of it. When, in the 1980s, Japanese textile manufacturers realized this, at last they were able to make close synthetic copies of natural silks: they called them Shin-Gosen (‘New Feel’).

      Lucretius was not the only poet whose imagination was caught by these natural phenomena. In his poem ‘Greatness in Little’, the 17th-century English poet Richard Leigh was intrigued by tiny things, long before such a fascination could be satisfied. At one point he bursts into praise of minuteness itself:

      Ah, happy littleness! That art thus blest,

      That greatest glories aspire to seem least.

      

      Even those installed in a higher sphere,

      The higher they are raised, the less appear…

      Bio-inspiration usually works at the nanolevel, but that does not make it synonymous with nanotechnology. Most nanotechnology is not bio-inspired; it is the province of materials technology, comprising things like smaller electronic components and nanoparticles in cosmetics and systems for delivering targeted doses of drugs. Another name for bio-inspiration makes clear the distinction: bio-inspiration is ‘nature’s nanotechnology’.

      What is especially interesting about nanotechnology and bio-inspiration is the existence of hybrid technologies – systems in which one part comes from technical nanotechnology and the other part