Web of intrigue

Scientists are on Spider-Man's trail in an effort to perfect a super-strong material, writes Mark Henderson. But what does all this have to do with Webster and Peter, a pair of Nigerian billy goats?

If the reviewers are to be believed, Tobey Maguire, a young American actor who has never before played anything approaching a teen heart-throb, makes a fine Spider-Man. An inspired piece of casting, he is every bit the geeky outsider that was Peter Parker - the awkward, bullied teenager who, on being bitten by a radioactive spider, acquired the remarkable powers of perhaps the most popular of all the superheroes created for Marvel Comics by Stan Lee.

However, Jim Kakalios, professor of physics at the University of Minnesota, the Spider-Man movie, released in the UK this week, has something missing. While there is nothing wrong with Maguire's love interest - a real Marvel character, Mary Jane Watson, played by Kirsten Dunst - Kakalios, a true comics buff, always preferred another of Peter's girlfriends, Gwen Stacy, who met a tragic end. And every semester, he introduces a new crop of undergraduates to physics through the story of her death.

Gwen had been kidnapped by the Green Goblin, Spider-Man's arch-enemy (played in the film by Willem Dafoe), and taken to the top of New York's George Washington Bridge to lure the hero into a trap. As Spider-Man approached to save her, she slipped and fell towards the river 300 feet (91 metres) below. Using his "web-shooter" guns, he shot a thread of strong spider-silk to catch his love just inches short of the surface, but when he hauled her back up, Gwen was dead. The shock of the fall, the Goblin taunted, meant she was dead before the thread had even reached her.

Not so, says Kakalios: try telling that to any skydiver, who would freefall for much longer while surviving unharmed. But Gwen, in any case, was doomed. Spider-Man's web would have broken her fall within the space of a few feet, slowing her from 95 mph to a stop in fractions of a second. The deceleration of 10G - more than that generated in a space shuttle launch - would have snapped her unrestrained neck instantly. "Marvel were right that Gwen would have died - they just had the wrong reason," he says. "It's a great example that can teach some basic physics."

Kakalios is not the only researcher to be captivated by the science of Spider-Man. His superpowers, and their relationship to the abilities of true arachnids, have also been analysed by Bob Weinberg and Lois Gresh, whose book The Science of Superheroes is published by John Wiley in Britain later this year. While Marvel comic writers always tried to give their characters powers with some foundation in science, in Peter Parker's case it might be just as well they didn't. A true Spider-Man, Weinberg and Gresh reason, would be rather a poor superhero: slow, clumsy and weak. He might be able to scale the odd skyscraper or two, but not while wearing his trademark spandex. "The powers acquired by Peter, supposedly those of a gigantic human spider, bear only a faint resemblance to those of real spiders," Weinberg says. "The problem with Spider-Man isn't that he's improbable, but that he's inaccurate."

A radioactive spider - updated to a genetically modified one in the film - is supposed to have given Peter five powers: strength, speed, agility, grip and a mysterious "spider-sense" that warns him of approaching danger. Unfortunately, spiders are not particularly strong, fast or agile for their size, and they are also rather cowardly and inefficient when it comes to hunting. "In nearly all circumstances, spiders avoid attacking anything approaching their own size as they are miserable fighters," Weinberg says.

Hunting spiders do have the ability to grip smooth surfaces, using a network of super-fine hairs called a scopula. These hairs, like those on the feet of geckos, are so small that they can use the forces that bind molecules together to generate astonishing sticking power. There is little doubt that a human being with such hairs would be blessed with prodigious climbing ability. Spider-Man, however, would still have a problem: he wears gloves and boots while in crime-fighting costume. "When he started wearing a costume, we can only assume that the material used for his gloves and boots was porous enough to allow fine hairs to pass through," Weinberg says.

Spider-sense, however, is not quite as ridiculous as it sounds. Spiders are also covered in very sensitive hairs called setae, which can detect disturbances in the air made by their prey. "Endowing a human being with such finely tuned powers could result in a heightened feeling of awareness that would be the equivalent of Spider-Man's spider-sense."

One aspect of Spider-Man's powers, at least, passes scientific muster with flying colours - to the point at which real researchers are even seeking to emulate it. The superhero's web-shooters - wrist-mounted guns that generate threads of spider-silk - might have been replaced by an organic ability to make silk from his wrists in Maguire's movie character, but they continue to intrigue scientists. Spider-silk is one of the toughest fibres known to man, weight-for-weight five times stronger than steel. It is as hardy as Kevlar, the man-made fibre used in bullet-proof vests, but lighter and more elastic. A single strand as thick as a washing-line could stop an F-16 fighter jet in its tracks, researchers say. A scientist who could replicate Peter Parker's web-shooter mix would have a perfect material for everything from medical sutures to heavy-duty cables and space station parts.

The obvious way to obtain this material would be to farm spiders like silkworms, harvesting the strands they produce to spin cables from their webs. Every effort to do so, however, has foundered on the contrary and territorial nature of the arachnids. "It's like farming tigers - they eat each other," says Jeffrey Turner of Nexia Biotechnologies in Montreal, Canada.

Enter a pair of Nigerian dwarf goats named Webster and, perhaps appropriately, Peter. Thanks to advances in molecular biology by scientists from Nexia, the US military and the University of Wyoming, and the pair of Canadian billies, mankind is closing in on a means of emulating Spider-Man's web-shooter technology without relying on obstreperous arachnids.

Webster and Peter are no ordinary goats. The animals are genetically modified, carrying extra genes from orb-weaving spiders that make spidroins I and II - the proteins used in dragline silk, the strongest of the varieties. These silk proteins can be extracted from the animals, and spun into BioSteel - a water-insoluble fibre that matches dragline natural silk for toughness and elasticity, though it has a slightly lower tensile strength.

Webster and Peter, both males, are the founders of what may eventually become a biological spider-silk factory: they have now sired a herd of more than 50 female offspring, who will produce the necessary proteins in their milk. Every bucket of transgenic goat milk - first being produced this summer - will contain enough protein to spin hundreds of metres of silk. In a recent paper in the journal Science, Nexia has also reported successfully adding the spider-silk genes to cow udder cells, paving the way for an even more spectacular yield. "Mimicking spider-silk properties has been the Holy Grail of material science for a long time, and now we've been able to make useful fibres," says Turner. "Having achieved this proof of principle, Nexia has now moved towards commercial development for multiple applications such as medical sutures, biodegradable fishing lines, soft body armour and unique material composites. It's incredible that a tiny animal found literally in your backyard can create such an amazing material by using only amino acids, the same building blocks that are used to make skin and hair. Spider-silk is a material science wonder - a self-assembling, biodegradable, high-performance, nanofibre structure one-tenth the width of a human hair that can stop a bee travelling at 20 miles per hour without breaking. Spider-silk has dwarfed man's achievements in material science to date. Tom Clancy mentioned in one of his novels that police will be wearing soft body armour in 2010. I think we'll be there long before then."

The process is environmentally friendly, because it mimics what takes place in the natural world, according to Costas Karatzas, vice-president of research and development at Nexia. A silk factory would consist only of a field of goats, and facilities for extracting the protein and spinning it into fibres. "The results are remarkable," he says. "First, we were able to produce monomers and spin fibres in an aqueous environment thereby mimicking the spider's way of spinning silk, a process that has been perfected through 400 million years of evolution. Using these water-based BioSteel solutions for large-scale fibre spinning would be considerably more environmentally friendly than using harsh solvents such as those used for more synthetic fibre manufacturing. Second, the material from mammalian cells was spun into fibres with significant toughness. Scientists have been successful in producing spider-silk proteins in bacteria and yeast in the past, but for a number of reasons, have been unable to spin fibres with appreciable properties."

Like Peter Parker and his web-shooters, that problem has now been solved - and Clancy's prediction, as Turner suggests, could soon be fulfilled. Policemen and soldiers may be unlikely to choose skin-tight red for their uniforms, but they may soon, in a sense, become real Spider-Men.





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