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

The organs of minute insects and the parts of plants are revealed as wonderfully tooled artefacts. Bio-inspirationists constantly have to track back and forth between the nanorealm and the everyday scale of things. According to the Russian novelist and serious amateur lepidopterist Vladimir Nabokov in Speak, Memory, this is an intrinsically artistic activity:

      There is, it would seem, in the dimensional scale of the world a kind of delicate meeting place between imagination and knowledge, a point arrived at by diminishing large things and enlarging small ones, that is intrinsically artistic.

      When the first pictures were seen, the question of how nature achieved these wonders of micro-engineering was completely off the agenda – scientists could only goggle at the structures. But now we know a lot more about how nature creates such shapes. The Gecko’s Foot is the story of how we are closing in on this last frontier of natural exploration.

      The nanoworld is like a complex jigsaw puzzle in three dimensions. We try to piece it together by viewing it with different magnifications and techniques. Behind the picture we can see with the unaided eye, there is another picture we have to zoom in on with the light microscope; behind that is a more detailed picture that we need the electron microscope to see; beyond that is the picture revealed by X-rays; and there are new types of microscope, such as the atomic tunnelling microscope, that all add information to the puzzle. To add to this, our knowledge of chemistry also sheds light on the three-dimensional structure. By combining all the information, we come to a picture that begins to approach completeness.

      In retrospect, it seems curious that we have been ignorant for so long about how nature makes stuff. While we are pretty good at making intricate structures ourselves, when it comes to the miracles of the human body our role in the construction process is crude andlumbering. Anne Stevenson’s poem ‘The Spirit is too Blunt an Instrument’ makes this point:

      The spirit is too blunt an instrument

      to have made this baby.

      Nothing so unskilful as human passions

      could have managed the intricate

      exacting particulars…

      

      Observe the distinct eyelashes and sharp crescent

      fingernails, the shell-like complexity

      of the ear, with its firm involutions

      concentric in miniature to minute

      ossicles. Imagine the

      infinitesimal capillaries, the flawless connections

      of the lungs, the invisible neural filaments…

      So, if not the spirit, what is nature’s organizing principle? How does nature create intricate structures? There is still much to learn and our own attempts at mimicking these processes are fumbling, but we are now on the trail.

      To understand why the realm of bio-inspiration is such a terra incognita, something really new under the sun, we need to look at the two great currents of 20th-century science. So powerful were these two prongs of attack that many people were dazzled into thinking that they revealed all we needed to know about the material world. These sciences were nuclear physics and molecular biology. Both ignored the multiplicity of the natural world – the several million species of living creatures (some estimates go as high as 30 million or more), all with different shapes, sizes, habits and curious adaptations; the more than 24 million known chemical combinations of the 92 natural elements; the architecture of matter in the honeycombs of the beehive, the fantastic filigree forms of the radiolarians of the ocean, and the interlocking spirals of a sunflower head. These were cast aside in the search for the ultimate, universal components and principles of matter (physics) and the chemical unit and mechanism of genetic inheritance in biology.

      The idea behind these quests was that if successful, they would somehow explain everything else. And, of course, they were successful. Nuclear physics uncovered the unexpected power of nuclear forces and molecular biology determined the mechanism of inheritance: a precise sequence that has a chemical form (the DNA molecule) but which functions as a code for the synthesis of proteins, nature’s prime functional substances.

      But, dramatically brilliant as these sciences were, they left enormous gaps. They did not begin to explain complex forms of nature, nor did they determine the composition of these forms. What the physics and biology obscured was the fact that to create functioning organs, the fundamental building blocks of atoms and molecules have to be synthesized into large structures whose properties cannot really be explained by a knowledge of which molecules compose them. The biologist Helen Ghiradella wrote in 1991, just before the bio-inspired explosion:

      Many of us working in biological fields have perhaps unconsciously assumed that small things must be simple, at least more accessible to human understanding than those on a human scale. This may not be the case, and indeed, the further we investigate the more complexity we seem to find.

      When, as a schoolboy in the early 1960s, I became fascinated by chemistry, what I wanted to know was: What are familiar objects made of? How is a tiny insect engineered from biological materials? What is the chemical structure of wood? What, in chemical terms, is a spider’s web? In The Periodic Table, Primo Levi beautifully expressed this chemist’s lust to know the fabric of the world:

      Everything around us was a mystery pressing to be revealed: the old wood of the benches, the sun’s sphere beyond the window panes and the roofs, the vain flight of the pappus down in the June air. Would all the philosophers and all the armies of the world be able to construct this little fly?

      But, at the time, chemistry had no answers to these questions. Whenever such structures and substances were mentioned in textbooks, the explanations petered out in sentences such as: ‘The hardness of the insect skeleton is due to the chitin being impregnated with another substance, called sclerotin or cuticulin; but not much is known about it chemically.’ There were some successes in getting close to nature. Nylon, for instance, invented in 1937, imitated the chemical bond of natural protein fibres, but natural proteins such as wool, silk and spider silk were known to be much more complex than nylon. While the nylon molecule has the same chemical unit, linked nose to tail thousands of times, natural silks have different amino acid units, linked nose to tail in a complex non-random pattern. Despite a concerted effort over the last 20 years to determine the structure of, and replicate, spider silk, it is still not fully understood.

      Although science has been successful in uncovering things not directly known to our senses, the mindset required to solve the problems of nuclear physics and genetic inheritance tends to be impatient of such questions as: What lies between the molecular realm and the objects we can see? The great early 20th-century nuclear physicist Sir Ernest Rutherford notoriously used to say that ‘all science is either physics or stamp collecting’. But our new science has arisen largely from the very stamp collecting Rutherford despised – descriptive biology, investigations of the habits of strange creatures, comparative studies of the microstructures of leaves.

      For a Rutherford, these meanders off the central pathway were expected to be explained fully by the fundamental laws of physics. And when his kind of particle physics was at the forefront in the mid-20th century, there were no techniques available to investigate larger-scale phenomena.

      The atoms of physics and chemistry are very small (about one ten billionth of a metre in diameter) and until 1971 this was far too small for any kind of microscope to see. Their size and properties were inferred from experiments on much larger quantities than single atoms: 1 gram of carbon contains about fifty thousand million million million atoms