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

substances from cellulose by several processes, the best-known being rayon (1891).

      The potential of silks in one of the toughest applications imaginable was realized in the late 19th century by a physician in Tombstone, Arizona: ‘In the spring of 1881 I was a few feet distant from a couple of individuals who were quarrelling,’ George Emery Goodfellow wrote in his diary. ‘They began shooting.’ Two bullets pierced the breast of one gunman, who expired from his wounds. But, on examining the body, Goodfellow found that, ‘not a drop of blood had come from either of the two wounds’. He noted that ‘from the wound in the breast a silk handkerchief protruded’. When he tugged on the handkerchief, it came out with a bullet wrapped inside. Evidently, the bullet had torn through the man’s clothes, flesh and bones but had failed to pierce his silk handkerchief. Intrigued by this discovery, Goodfellow began to document other cases of silk garments halting projectiles – including one incident in which a silk bandanna tied around a man’s neck kept a bullet from severing his carotid artery.

      If silk was ever going to be used seriously for such applications it needed to be made in quantity. The mimicking of natural silks on a commercial scale began with the invention of nylon in 1937. Nylon is derived not from plant products but from very small chemical units, linked together to form long-chain molecules. Such compounds, now ubiquitous in modern civilization, are called polymers. In nylon, the link – the amide group – was the same as that in natural silks although the rest of the molecule was very different. Nylon has a much more regular structure than natural silks.

      The first serious flak-jacket silk was kevlar, a tougher variant of nylon, invented in 1963. Even with nylon, kevlar and other fibres established as industrial staples, the superior properties of spider silk were alluring, but no bulk industrial or military use was proposed until very recently. The first serious modern application was very small scale. In the Second World War, single fibres of spider silk were used as cross-hairs for accurate range-finders – it came from black widows in the USA, garden spiders in the UK. Pioneer spider-silk researcher David Knight tells the story of the major US chemical company Du Pont, inventors of nylon and kevlar, who supplied a spider-silk sample to the US Army during the war, hoping for an order. Three years later, they politely enquired about the silk and asked whether the Army would be making an order. ‘Oh, we don’t need any more,’ they were told, ‘what you sent was fine.’

      The picture changed dramatically, at least in prospect, with the arrival of genetic modification (GM) technologies in the late 1970s. In GM, a gene can be inserted into a foreign organism; the organism will function normally and produce the proteins programmed by that gene. So, in theory, if you took the gene for spider silk, and inserted it into an animal, you could make industrial quantities of silk.

      Work began on this project in the 1980s and was bedevilled by nature’s cussedness. Spider-silk genes turned out to be harder to handle than the insulin gene, GM’s first great success. But, in June 2002, Nexia Biotechnologies in Quebec, Canada, claimed that they were able to produce industrial quantities of spider silk from the milk of genetically engineered goats. The story had a strange blend of hard military exploitation and New Age greenery. On the one hand, the US Army had been working on spider silk for many years; Nexia’s silk, named BioSteel^®, was developed under an Army contract for flak jackets and one of the two herds of modified goats was kept on a former United States Air Force B52 bomber base at Plattburgh, New York State. On the other hand, Nexia’s President and CEO, Jeffrey Turner, waxed lyrical about this new fibre produced from meadows, goats, sun and water and spun at room temperature from a watery solution. Nylon and kevlar, the closest things we have to spider silk, are made using toxic chemicals and high temperatures and they generate toxic wastes. Turner said: ‘We use water and hay; to make nylon – which has a half-life of 5,000 years [which means it’s not biodegradable] – you have to sink a hole in the ground. That’s not the kind of world I want to leave my kids.’

      If we could manufacture large quantities of spider silk and spin it the way the spider does we would have a very special material. But 16 months on from the excited press reports of June 2002 the spider-silk story looked very different. The US Army withdrew from its collaboration with Nexia because BioSteel, as it then was, could not meet their requirements for quality or quantity.

      By mid-2004, Biosteel had been downgraded even further. Development of spinning for general yarn and fabric was suspended due to the ‘ongoing technical challenges of producing bulk, cost-competitive spider-silk fabrics with superior mechanical properties’. On 8 March 2005 this particular strand of the spider-silk story was fractured. Nexia’s principal asset Protexia^®