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Lab Spins Artificial Spider Silk, Paving the Way to New Materials

Bijal P. Trivedi
National Geographic Today
January 17, 2002
 
Tougher than Kevlar and stronger than steel, spider silk has long
intrigued engineers and scientists because of its potential industrial
and medical applications.

Now, a biotech company in Canada has
developed a method for producing artificial spider silk by inserting the
genes for spider silk into the cells of mammals.




In experiments so far the researchers have produced spider silk by inserting the gene into the genome of cows and hamsters. The company plans to also insert the silk-producing gene into goats with the aim of collecting silk proteins from goat milk.

The scientists at Nexia Biotechnology in Quebec reported their new method of creating a type of spider silk, known as "dragline," in the January 18 issue of the journal Science.

Orb-weaving spiders generally produce about seven different types of silk, which they use for different purposes. Scientists are most interested in dragline silk, from which a spider constructs the outermost circle of a web and all the spokes radiating from the center.

"Dragline silk is also the silk spiders spin as they fall from the ceiling—it's their lifeline," said Randolph Lewis of the University of Wyoming in Laramie.

Many Potential Applications

The strength and elasticity of spider silk make it a good candidate for a broad range of medical and industrial applications, including artificial tendons and ligaments, sutures for ophthalmic and micro surgery, biodegradable fishing line, bulletproof vests and lightweight body armor, parachute cords (particularly when dropping tanks or other heavy objects), and cables used to help stop planes as they land on aircraft carriers.

Yet until now, manufacturing silk fiber has been surprisingly difficult.

Natural dragline silk is made up of two proteins. They were identified a decade ago by Lewis and his colleagues, but attempts to use the two genes that encode these proteins to mass-produce spider silk were unsuccessful.

According to researchers, one reason silk is so difficult to make if you're not a spider is because the proteins are so large. Bacterial cells are often used to make artificial proteins in the lab. In this case, however, the spider silk proteins are too large and the cells cannot make and release large quantities. So the researcher tried using mammal cells instead.

Manufacturing large proteins is a challenge for any cell. To overcome that obstacle, the Canadian scientists used a shortened version of one of the two genes for dragline silk (called ADF-3) and inserted it into hamster and bovine cells, which are capable of manufacturing and releasing high quantities of a protein.

After manufacturing and collecting a quantity of the silk proteins, the Nexia scientists sent the material to microbiologist Steven Arcidiacono of the U.S. Army Soldier Biological Chemical Command in Natick, Massachusetts, where researchers had developed a "spinning" technique.

The proteins were placed in a syringe and squeezed through a tiny tube, which forced the proteins into the shape of a silk fiber. "You can actually see the silk fiber. It looks a little thinner than a human hair—it's about ten to 40 microns in diameter," said Arcidiacono.

Lewis said the resulting fiber is similar to natural spider silk but not a duplicate. "The silk they have spun is about three times more elastic and not quite as strong as natural spider silk," he explained. "It is short of the real thing, but better than anything everyone else has been able to do."

The diameter of Nexia's silk is slightly larger than a spider's. Thinner silk tends to be stronger, but scientists are not sure why.

Manufacturing Benefits

One of the biggest advantages of Nexia's technique, Lewis said, is that the silk proteins that are made in mammal cells do not clump or gel in water, which would make it impossible to shape the proteins into a fiber. "The rest of us had to use really toxic chemicals to keep silk proteins dissolved," said Lewis. "This opens the possibility for environmentally friendly manufacturing."

Lewis is now trying to insert silk genes into plants, specifically alfalfa, which would be a cheap way of producing artificial spider silk. Alfalfa was chosen because it produces large amounts of protein (the plant is 24 percent protein by weight).

"One of our goals is to create designer silks that are stronger and stretchier than spider silks," said Nexia scientist Anthoula Lazaris, the lead author of the report.

Among orb-weaving spiders—about one quarter of all spider species—the genes responsible for producing dragline silk have remained essentially unchanged through 125 million years of evolution, said Lewis.

Lazaris said: "Mother Nature knows what she's doing, and our goal is to bio-mimic her creations."

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