On the spider's trail

November 27, 1998

The humble garden spider has inspired an international group of scientists aiming to develop the toughest materials yet.

Spiders' silk is one of the toughest materials known to man, able to absorb more energy for its weight before breaking than almost anything else, said David Knight, formerly reader in biological sciences at King Alfred College, Winchester, and until recently visiting professor at the University of Aarhus, Denmark.

It is up to three times as tough as Kevlar, the toughest synthetic material, used in the manufacture of bullet-proof vests, and that in turn is tougher than steel. Now scientists are on the trail of exactly how spiders spin their silk, in the hope of mimicking this in an industrial process.

The team at Aarhus, including Dr Knight and Fritz Vollrath, professor of zoology, have been studying the English garden spider and the much larger Golden Palm from the Pacific. Using a polarising microscope, they have looked at the protein feedstock which is formed in the spider's silk glands and then drawn to form silk thread. "To our great astonishment, we found that the silk feedstock was organised into a beautiful liquid crystalline pattern in the part of the duct just in front of the region in which the thread is drawn. This tells us exactly what sort of liquid crystal polymer is used and how the thread is formed," said Dr Knight.

"Manmade systems use a restriction die, a fine nozzle through which the liquid polymer is pumped to form a filament. But the spider doesn't do that. Instead it has a narrow tapered duct between the gland and the outside of the body. The silk thread is pulled out of the duct directly rather than pushed through a restriction die."

Dr Knight believes a membrane which lines the inside of the duct provides a cue for the ordering of the liquid crystals. These crystals have a "beautiful chevron-like pattern" and are without the imperfections so often seen in liquid crystals. "This, we think, is one of the reasons why spider's silk is so tough," he said. "The polymer industry is going to be quite excited about this. It suggests a different way of spinning Kevlar which may increase its strength."

The European Science Foundation this week announced a three-year Europewide scientific network co-ordinating research on the properties and production of silk. Funded to the tune of around Pounds 50,000, the network, which Dr Knight is co-ordinating in Britain, aims to understand better the process of spider silk production, more particularly silk-protein folding and the ultrastructure of the resulting fibre.

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