Legend has it that when the mighty ruler Genghis Khan (Jen-gis Kon) conquered Asia, his soldiers were protected from enemy arrows by very special clothing. Their leather garments were interwoven with one of the strongest substances then known to humans--spider silk!
Eight hundred years later, scientists have still not invented a thread more durable than the stuff that creepy, crawly spiders use to make their webs. But biologists trying to copy nature's strongest fiber are making great progress. Now the U.S. Army plans to use one of the Great Khan's tricks: making bulletproof vests woven with artificial spider silk.
Strength Plus Stretch
What makes spider silk so remarkable is its unique combination of strength and stretch. Spider silk is as strong as Kevlar, the fiber now used to make bulletproof vests, but far more elastic.
The web of a golden silk spider is strong enough to trap a bird. Engineers have calculated that a web woven of spider silk the thickness of a pencil could stop a jet in midair!
"When you think about the size and speed of a flying bee, the web that catches it is absorbing a lot of energy," says Jean Herbert, an Army scientist in Natick, Massachusetts. Herbert is researching ways to use the tough fiber in everyday objects. Among the possibilities: jeans that don't wear out, car and truck bumpers that resist dents and bridges that withstand earthquakes.
Unlike silkworms, spiders cannot be raised on farms. (One reason: they tend to eat one another!) So scientists are inventing ways of making spider silk without spiders. The ability to spin a web is controlled by certain genes inside the cells of spiders. Researchers at Monsanto and DuPont chemical companies have made copies of these genes and put them into certain easy-to-grow bacteria. The scientists' goal: bacteria that can churn out spider silk.
Agricola, a small company based in San Francisco, California, has succeeded in transplanting the golden silk spider's silk-producing process to bacteria. Now Army scientists, using Agricola's research, have coaxed bacteria colonies to create the first few inches of golden-silk-spider thread.
Breakthroughs like this have created a Frankenstein's sewing kit of man-made fibers. But so far, none of the fibers have the strength of natural spider silk. Transplanting spider genes is a sticky business. The genes don't always act exactly the way they would in a living spider, so the silk is not as strong or elastic as the real stuff.
For now, the surest silk-production method is the one that Genghis Khan supposedly used--spiders themselves. "I never step on spiders," says John O'Brien, a chemist working to produce spider silk for DuPont. "I have too much respect for them."