The Gecko’s Foot: How Scientists are Taking a Leaf from Nature's Book. Peter Forbes
information is contained in a very tiny fraction of the cell in the form of long-chain DNA molecules in which approximately 50 atoms are used for one bit of information about the cell.
It is very easy to answer many of the fundamental biological questions; you just look at the thing! You will see the order of bases in the chain; you will see the structure of the microsome. Unfortunately, the present microscope sees at a scale which is just a bit too crude. Make the microscope one hundred times more powerful, and many problems of biology would be made very much easier.
It must have seemed crazy to many at the time. Feynman blithely asserted that the whole of the Encyclopaedia Britannica could be stored on the head of a pin. Now we can believe this because even if we have not quite got it down to a pinhead, we are not far off with our electronic disk-storage systems. But the micro-electronics revolution was only the first stage of the drive into micro-space. At the time, Feynman looked to biology to make his point because he knew that nature did her most intricate work on a tiny scale. But he also knew that most of the detail was tantalizingly out of reach.
A gecko climbs a vertical glass wall sure-footedly; when it reaches the ceiling it steps onto it and continues, upside-down, without difficulty. From the other side of the glass you can see transverse bands of tissues crossing its feet that alternately grip and release in a mini Mexican wave across the surface of the foot. A leaf of the sacred lotus unfurls in muddy water; as it rises, all the mud rolls off as if magnetically repelled, leaving a pristine surface. From a quarter of a mile away you can see the brilliant blue wings of a Morpho rhetenor butterfly; they are not just blue – they shimmer with an iridescent sparkle – but analysis reveals no blue pigment in the wings. That same Morpho butterfly takes off and jinks through the air, changing direction abruptly; until 1996, scientists were at a loss to understand how insects like this could fly. According to the well-tried aerodynamic theories that took a Jumbo into the air or flew Concorde at twice the speed of sound, insects did not generate enough lift to fly, but fly they do. And when a heavy insect thuds into a spider’s web constructed from filaments about one tenth the diameter of human hair, the web distorts, brings the fly to a standstill and then returns to its original shape, the fly held fast in its sticky capture threads. Human engineering suggests that even if such a gossamer structure could catch an insect, it ought to fling it out again in recoil.
These creatures obviously possess skills and attributes beyond conventional engineering. But if we could find out how they achieve what they do, and learn how to utilize their techniques, it would extend our capabilities unimaginably. But the mechanisms behind these feats were hidden in structures so tiny that no microscope could observe them, and their chemical structures were so complex they defeated all attempts at analysis. As for creating man-made substances with the same properties: it was out of the question.
The dramatic powers of adhesion, self-cleaning, optical wizardry, tough elasticity and aerodynamics shown by these creatures are all highly prized by technologists. Scientists have long admired nature’s engineering skills. Indeed, the precision of some of nature’s gadgets takes the breath away: the stinging cells of jellyfishes; the jet engines of squids and cuttlefish; the marine creatures (and the land-based fireflies) that produce light without any heat. But there was no simple way of translating natural mechanisms into technical equivalents.
Nature was thought to use an entirely different set of principles to those of the engineer. Nature was soft and wet, worked at room temperature, and made her gadgets out of incredibly complex substances. While the human engineer instinctively reaches for metals to heat and beat into shape, nature goes for proteins that are grown inside living cells at body temperature. A single protein molecule is made from hundreds or thousands of smaller component molecules, virtually all of which have to be in precisely the right place for the protein to work.* A protein molecule is first made as a long chain and then it folds up precisely into a three-dimensional ball, like a piece of wet origami.
Nanotechnology has brought nature and engineering far closer together. If Feynman’s 1959 talk is seen as the beginning of nano-technology, natural mechanisms were taken to be the epitome of the science right from the beginning. And now we don’t just stare at creatures in amazement, wondering ‘How do they do it?’ Thanks to genetic engineering and a host of new techniques, we can now start to unravel nature’s nanoengineering and produce engineered equivalents for it. This is bio-inspiration.
What makes bio-inspiration possible is the miracle that nature’s mechanisms do not have to be ‘alive’ to work. In the 19th century, there was a doctrine known as ‘vitalism’ which held that all living things had a magical property – the élan vital – that could not be reduced to material science. Even the waste products of living things were thought to be fundamentally different from mineral substances. The doctrine began to crumble in 1828 when the waste product urea was made in the laboratory from two ordinary chemicals of mineral origin. Thereafter, the idea of vitalism suffered blow after blow and now no scientist seriously believes that living things are, in a material sense, any more than the chemicals that comprise them. The property of life derives from the enormous complexity of the way the chemicals are organized, and not from an élan vital; some of the principles of this organization will become clear as the book proceeds.
Many of nature’s most ingenious systems can continue to work outside living cells, in a test tube, and can be directed to work in novel ways to suit our purposes. For instance, in 1997 it was discovered that, although proteins will never meet such substances in the living cell, in the laboratory they can bind to inorganic materials such as gold and silver. Not only that but new proteins can be engineered that can bind to all the materials used to make computer chips. And since proteins are structured on a much smaller scale than silicon chips, they could act as templates for smaller microchips – nanochips.
Proteins have active centres, nooks and crannies precisely fashioned so that only one specific chemical can fit into them. When, in the whirling fluids of the cell, the one and only right chemical happens to come along, it becomes tightly bound to the protein. In living cells, proteins bind some chemicals, let others pass through pores, and, in general, regulate the traffic within the cell and facilitate chemical reactions. The full implications of this are spelt out in Chapter 6 but for now the point is that we have come so far from vitalism that the old division between living and non-living substances is breaking down – we can engineer hybrids between the two.
That there are no new frontiers is a weary cliché of our time: the ancient thrill of unspoiled places on Earth has given way to the fact of life that people can and do fly anywhere anytime. The dream of new worlds in space has retreated in the face of the barrenness of the Moon and Mars; the glorious new dawn of modernism in the Arts in the early 20th century led only to the stylistic emporium of postmodernism in which any retro style could be taken up again for a few years, given a whirl, then dropped. The decadence and satiation of our world is only too apparent. Scientifically, we have gone very deep – into the nucleus of the atom and the genetic code of all life – so what can be left to discover?
Bio-inspiration is a genuine new frontier. It is a growing body of techniques for making materials with novel and startling properties: surfaces such as paint and glass that clean themselves, fabrics that exhibit shimmering colour despite having no coloured pigments, fibres tougher (weight for weight) than nylon or steel based on spider silk, dry adhesives based on the microstructure of the gecko’s foot.
It is not just a new frontier because these properties are startling but because they have something in common. The mechanisms of most of these effects are caused by physical structures of a certain size: from one billionth of a metre up to one millionth of a metre (fig. 1.1). This is the nanoregion and the structures nature builds at this level we can call nature’s nanostructures. Until recently, the nanorealm remained relatively inaccessible to science and this may seem strange since scientists are able to manipulate subatomic particles millions of times smaller. And chemistry, a precise science with a growing inventory of more than 24 million discrete substances, operates at the size range just below the nanoscale.
The key to this paradox is that there is a huge gap between what we can infer about the size of atoms and molecules (and their even smaller constituents