Scientists tease out spiders' secret
Monday 24 October 1994
According to Dr Alexandra Simmons, of the biotechnology programme at Cornell, the US Army 'is looking into the properties of these fibres as a substitute for Kevlar in bullet- proof materials'.
Under the leadership of Lynn Jelinski, professor of engineering at Cornell, the researchers 'painted the silk with heavy hydrogen', Dr Simmons said.
They fed golden orb-weaving spiders a diet specially labelled with deuterium, a form of hydrogen which differs slighty from the naturally occurring version. The deuterium was incorporated into the proteins in the spiders' silk and this allowed the researchers to identify the orientation of the fibres in the silk to study how they stretched and relaxed. The surprise result of their work - recently reported at the national meeting of American Chemical Society - was that 'all the silk is somewhat crystalline', Dr Simmons said.
This differs markedly from all synthetic fibres which tend to be amorphous - there is no regular, ordered, structure into which the atoms are arranged.
Synthetics, Dr Simmons said, tend to consist of 'small crystals surrounded by a jumbled spaghetti'.
A strand of spider silk, however, tends to consist of areas where the protein molecules are well packed in crystals alternating with more elastic components, but even in the elastic areas, 'we have no evidence for very amorphous regions', Dr Simmons noted.
The unique structure of spider silk gives it the tensile strength of a steel fibre of the same diameter, yet it can stretch and rebound from at least 10 times its original length - something no metal or synthetic fibre can achieve. But according to Dr Simmons, the group's findings on the structure of spider silk 'will require a new way of thinking about how elasticity is generated'.
The genes which produce the protein in spider silk have aleady been located and partly analysed, by Randy Lewis at the University of Wyoming. Coupled with the research at Cornell, this could open the way for scientists to develop a synthetic gene that still retains all the necessary structural components.
Such a gene could then be stitched into soyabean or maize crop-plants to produce the silk from biomass. Farming spiders themselves is not a viable proposition: it takes more than 400 spiders to produce enough silk for one square yard of cloth.
But the spider has one final trick up its spinneret, according to Dr Simmons. The polymer fluid undergoes some sophisticated mechanical processing during its journey from the gland in the abdomen where it is produced to the organ that releases silk. 'The spider converts a protein solution into an insoluble engineering- quality polymer simply by drying through a long complicated tube,' Dr Simmons said.
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