A web of desire

Why have cotton when you can have silk? Perhaps the real question should be: why reel it off the silkworm cocoon when you could make it in a factory?

Professor Fritz Vollrath and a team of researchers in the Department of Zoology at Oxford University are investigating techniques for producing artificial silk. Instead of the silkworm, the scientists have focused their attention on another silk producer – spiders.

Web spider silks have many exciting properties. They can be incredibly tough, with a capacity to absorb energy that equals the nylon filaments in bullet-proof vests. Yet spider silk is extremely eco-friendly: fully biodegradable, it is produced at ambient temperatures from water soluble, renewable materials.

“Spider silk is an amazing material, and I think we can copy it in the very near future,” asserts Professor Vollrath.

Molecular biology has already supplied the raw materials. Scientists insert the genes for the silk proteins into other cells. The proteins are then secreted into the milk of engineered goats or harvested from the leaves of modified plants. The problem then is to get from the liquid feedstock to useable threads.

As the spider already knows best, Professor Vollrath and his collaborator Dr David Knight decided to study the anatomy and function of the spider’s spinneret in more detail. His team also investigated the relationship between the structure of silk threads and their properties and the effects of temperature and spinning speed.

An extraordinary process appears to take place when the spider spins its skein. As the feedstock passes through funnels, ducts and valves to draw out a thread, the proteins line up, unfold, then refold in an extremely controlled manner to form cross links. The thread is almost indestructible.

“Protein folding is one of the biggest secrets in biology,” says Professor Vollrath. “No-one really knows how it happens and how you get from an amino acid sequence to a three dimensional structured protein. Not only do we hope to produce an artificial silk, but we may find some clues as to how protein folding occurs along the way.”

Prototype spinning devices are currently being prepared and a spin-off company will help to further the commercial applications of Oxford team’s research. “In a few years we hope to be able to produce silk with predictable properties. Predictability is the first important goal.”

Medicine will probably benefit first from Professor Vollrath’s material. “Silk from silkworms is already used for stitches, but it contains an immunogenic protein that cannot be entirely removed; some people react when it is inserted inside the body.

“Spider silk would be a good replacement and would make sense commercially because you only produce small quantities for a high price.” Bulk textiles would be the last area to see artificial spider silk, he admits. It may be some time before you can buy a spider silk shirt.