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

of the expression). It was the triumph of chemistry that it was not necessary to see these tiny atoms in order to synthesize millions of new compounds whose precise structure is known.

      This chemistry of inference, working in the dark, so to speak, was the chemistry I was taught at school in the 1960s – experiments were carried out with simple substances, stuff you could grasp and whose properties were clear. I might bubble carbon dioxide through limewater, say; the result was a white precipitate of solid matter. I could filter and dry this and the result would be calcium carbonate, the chemical that chalk and limestone are made of. Running parallel to this palpable experience, the books would give you an equation for their reaction, in this case:

      Ca(OH)₂ + CO₂ = CaCO₃ + H₂O

      Like mathematical equations, these equations always balance because they represent the reactions between individual atoms and molecules, and nothing is ever lost in a chemical reaction. There is one calcium atom, four oxygens, two hydrogens, and one carbon on both sides of the equation. What happened in my test tube was this reaction, between individual calcium hydroxide and carbon dioxide molecules. And it was happening billions of times over to make enough of this substance for it to be visible to my eyes.

      I chose this reaction as an example because the simple minerals of school chemistry, such as calcium carbonate and silicon dioxide, turn out to be capable of forming structures of architectural complexity in living systems, many of which are to be found in the deep oceans. The extreme conditions to be found there – intense pressure and little light, the dispersed nature of prey, the single medium of water – have inspired some ingenious devices. The romance of the oceans is epitomized by the Venus flower basket, a sea sponge and a baroque extravaganza of mineral basketwork so ornate that Joanna Aizenberg, the biomineralization expert at Bell Labs, who is studying it for its fibre-optical properties, cannot yet see how such a structure can grow from an egg. A new frontier indeed! To its beauty and mystery have now been added the fact that it possesses in the long hairs that surround the base of its latticework some brilliantly effective fibre-optic filaments. These, in human engineering terms, are the conduits used for high-capacity telephone and internet lines. The Venus flower basket has evolved these structures to manipulate what little light there is on the sea floor (at least we think it has – as with much else about the creature, biologists are not entirely sure).

      Then there are the brittlestars, with primitive eyes that focus light through exquisitely engineered lenses made from single crystals of calcium carbonate (see Chapter 5). In these creatures, the crystallization of calcium carbonate is directed by proteins and this is one of the prime routes being explored in bio-inspiration: to direct the formation of engineered structures of minerals such as calcium carbonate and silica, using proteins, as nature does.

      But simple chemistry was inadequate to explain how proteins organize minerals to produce these complex forms. Proteins are, unlike calcium carbonate, very large molecules. The molecular weight of CaCo₃ is 100 D (D stands for ‘Dalton’ and is a measure of the relative mass of atoms and molecules, hydrogen being 1 Dalton) but a protein can contain thousands of different amino acid building blocks in one molecule, and the molecular weight might be 300,000 D.

      Although attempts to derive engineering solutions from natural mechanisms have only begun to be made in the last 15 years, earlier biologists came close to guessing their potential. Sir Alistair Hardy, in The Open Sea (1956), repeatedly marvelled at natural mechanisms as feats of engineering. This is Hardy on the stinging hairs found on many jellyfish:

      It is not a living thing; it is a dead structure, an elaborate tool made ready for work – and made to perfection – by the semi-fluid living substance of the cell. Here is something to wonder at, for it looks as if it were designed.

      Behind this you feel the lurking suspicion that we ought to be able to design such a structure. In this case, we haven’t yet done so but the action of biological springs like the jellyfish’s sting is definitely on the bio-inspired agenda. Hardy has the true spirit of bio-inspiration before its time. My second-hand copy of The Open Sea: The World of Plankton (The Open Sea is in two volumes, one on the world of plankton, the other on fishes) has an interesting history. It is stamped inside: ‘MoD Library Services: withdrawn from stock.’ These days, the Ministry of Defence is a principal funder of work in bio-inspiration. I hope they have bought a new copy.

      Bio-inspiration has an appeal denied to other cutting-edge sciences. Firstly, it involves some attractive creatures, adding an extra dimension to the allure of butterflies, geckos, lotus plants and the like. Then there is the utility of the products – this is a technology, not science for science’s sake. Bio-inspired solutions are often comprehensible in a way that much science is not: they involve structures whose functions are clear, even if they need a microscope to see them. Finally, some subjects of bio-inspiration are amenable to kitchen-table experimentation, as this book will demonstrate.

      Inevitably with a new subject, there is some uncertainty about the boundaries of bio-inspiration. Scientists working in bio-inspiration generally fall into one of two camps: biomechanics or materials science. Biomechanics is concerned with large-scale mechanisms, such as how insects fly, materials science with fine-scale structure and chemical composition. It is worth remembering that, historically, these two disciplines come from very different traditions. The materials scientists prefer the term ‘biomimetics’ for this new subject but the biomechanics don’t like this because it suggests to them a slavish copying of nature (mimesis = ‘copying’). When he lectures, Professor Bob Full, the ebullient master of animal locomotion at Berkeley, University of California, even has a slide with a big red slash through the word: ‘Biomimetics? No,’ he says, ‘Bio-inspiration is the way to do it.’ In an important sense Full is right. Scientists try to unravel nature’s mechanisms, but technologists use whatever will work. Bio-inspired technical products will almost certainly not mimic the actual materials used by nature. The self-cleaning Lotus-Effect^® (see Chapter 2) is the most advanced of these techniques in terms of coming to market, with several products available, but it does not use the actual substances found in lotus leaves.

      It is worth thinking about how nature and the human engineer went about producing their structures before we reached this point of rapprochement at which engineers are eager to learn from nature. Design in nature and in engineering are achieved by totally opposite methods. The human engineer can start from scratch, designing on paper something never seen before and then assembling the parts until it is all connected up and ready to go. For example, for birds to reach their present sublime level of design, it has taken millions of years of evolution. In the 1940s, aeroplanes made the abrupt jump of moving to jet engines from piston engines that drive propellers. The jet engine was perfected by Frank Whittle between its invention in 1928 and the first flight in 1941. If nature had wanted to evolve towards something similar there would have been an intermediate creature that could still fly by the old method while the new one was developing.

      Bob Full makes the point like this: ‘If I told you to take my ‘84 Toyota and make it the fastest car possible using any material that you have, you could make a pretty fast car if you could replace 20 things. But you can’t throw away the whole genome and start from scratch. That’s a pretty heavy compromise.’

      Put like this, it would seem that the human engineer holds all the aces. If, as a designer, nature is hobbled in this way, surely the human engineer ought to win hands down? But, despite her apparent constraints, nature has still produced devices for which engineers would give their eyeteeth. With regard to flight, for example, human aviation is impressive but in terms of manoeuvrability, the fly leaves a modern jet fighter standing, being able to turn a right angle at speed in only one twentieth of a second.

      We are fortunate that we can have it both ways, using nature when it has developed structures we can adapt, while at the same time retaining the engineer’s radical risk-taking advantage over evolution’s necessarily conservative processes.

      There are times when it seems that bio-inspiration should be called ‘technomimetics’: only too often physicists, engineers or chemists invent something; biologists then discover that nature has already invented it