Doing what a spider can

Medicine & Science

August 02, 2004|By Michael Stroh | Michael Stroh,SUN STAFF

If you walked out of Spider-Man 2 fantasizing about taming bullets and bad guys with a blast of spider silk, get in line: Arachnid-inspired scientists and engineers are way ahead of you.

Taking a cue from the comic-book superhero, some researchers have developed web-slinging weapons packing synthetic nets. The U.S. Coast Guard is working on a helicopter-deployed device capable of snaring criminals and terrorists on the high seas.

Others scientists are trying to unravel the molecular secrets of spider silk itself. The hope is that the silk - one of nature's strongest fibers - could someday be woven into objects ranging from impregnable body armor to wear-resistant ropes, parachutes and uniforms.

To that end, the Defense Department is bankrolling several efforts to make and spin spider silk in the lab.

"I think there's gonna be interest in spider silk forever," says Steven Arcidiacono, a molecular biologist with the U.S. Army Soldier Biological Chemical Command in Natick, Mass. "It's such a cool material."

Scientists were intrigued by the spider's capabilities long before Marvel Comics launched its popular character in 1962. Thinner than human hair and lighter than cotton, the strongest silk is three times tougher than Kevlar, the man-made material used in bulletproof vests, and five times stronger than steel cable.

The other thing that has drawn scientists to the material is how it's made. Unlike Kevlar, which requires intense pressure and poisonous sulfuric acid to produce, spiders can unspool silk at room temperature, under normal pressure, using little more than proteins and water.

But efforts to produce large quantities in the lab have progressed slowly, says Frank Ko, a textile engineer at Drexel University in Philadelphia who studies the material's mechanical properties.

"Spiders," he says, "are only ahead of us by a few million years."

Scientists long ago ruled out the most obvious solution to harvesting silk: "spider farms." Unlike mulberry-munching silkworms, whose shimmering fiber is prized in the fashion world, spiders are territorial carnivores. Cage them in a pen, says Ko, and they will soon consume each other.

Instead scientists have turned to genetics.

In 1990, a team led by molecular biologist Randolph Lewis at the University of Wyoming decoded the first pair of spider silk genes. The genes produce "dragline" silk. The strongest of the spider's seven silks, it's used to frame webs and as a lifeline when the insect dangles.

The next trick is to produce the proteins made by these genes. Nexia Biotechnologies in Montreal has created a flock of genetically engineered goats designed to churn out silk proteins in their milk. After processing, the company is left with a pure powder that it markets under the name BioSteel.

But at $1,500 a gram, the silk isn't cheap. And so the company has moved away from bullet-resistant textiles, concedes Nexia Chief Executive Jeffrey Turner. "We'll leave that to Spider-Man," he says. The company is now looking at applications ranging from super-strong composites to cosmetics for its silk.

At the same time, Nexia and others are also working to improve the economics by inserting the silk genes in crops including alfalfa and tobacco.

But churning out cheap silk protein is only part of the challenge, then scientists have to spin it.

In reality, spiders don't spin, they squeeze. Liquid silk protein is forced through fingerlike glands on a spider's abdomen called spinnerets. Spiders then stretch these filaments with their legs to align the silk protein molecules.

In 2002 researchers at Nexia and the U.S. Army announced in Science that by mimicking this squeezing process mechanically they created a filament that was a little stretchier than the real thing and not quite as strong.

Lewis, whose research is partially funded by the Defense Department, is now pushing silk research toward the next frontier: customized silks.

In a new paper published online last month in the journal Molecular Biology and Evolution, Lewis and his team report they have decoded the gene responsible for aciniform silk, which spiders use to swath their prey.

Swathing silk is more elastic than dragline silk. By comparing the genes responsible for each of the silks, Lewis says he can pinpoint the sections of genetic code responsible for each silks' mechanical properties.

With this knowledge, he and his team are constructing synthetic genes capable of spitting out a protein for completely novel silks not produced in nature.

Still, some engineers are side-stepping the challenges of natural silk and devising devices that are only loosely spider inspired.

Arnis Mangolds at Foster-Miller, an engineering firm near Boston. Miller has spent the last 15 years or so dreaming up various web-slingling weapons, mostly for the government.

One of the first was Webshot, a flaregun-like device that fires a 15-foot-diameter nylon net to subdue fleeing suspects. Tested in the late 1990s by several U.S. police departments, the device worked but never caught on, Mangolds says.

Still, it didn't stop him from producing variations in which the nets were slathered in pine tar to make them spider-web sticky.

Now he's working on the U.S. Coast Guard project, dubbed Boat Trap. This time, he and his colleagues have developed an X-shaped net designed to snare speedboats and other watercraft.

Packed inside an explosive-lined drum and dropped from a Coast Guard helicopter, it's designed to deploy just above the waves and gum up a boat's propeller shaft.

"People are still trying to figure out what you can do with nets," Mangolds says. "It's kind of in its infancy right now."

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