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Artificial Spider Silk Could Be Used for Armor, More

Brian Handwerk
for National Geographic Channel
January 14, 2005
 
On TV: Watch Explorer's Spider Sex Sunday, January 16, on the National Geographic Channel, 8 p.m. ET/PT

Scientists hope to soon be able to spin spider silk without the aid of spiders—achieving an age-old human quest to harness one of nature's most remarkable materials.

Randy Lewis is a professor of molecular biology at the University of Wyoming in Laramie. His team of researchers has successfully sequenced genes related to spider-silk production—uncovering the formula that spiders use to make silk from proteins. In the process the team acquired a better understanding of how the silk's structure is related to its amazing strength and elastic properties.

Their next task will be using what they've learned to spin spider silk themselves.

"Hopefully in the next month we'll start spinning fibers," Lewis told National Geographic News.

Scientists don't completely understand how spiders spin liquid protein into solid fibers. With their spinnerets, spiders somehow apply physical force to rearrange the proteins' molecular structure to turn the proteins into silk.

Understanding how spiders do this could someday result in new stronger and lighter materials that could replace plastics—and ease the cost to the environment that results from conventional plastic production. But duplicating spider silk in the lab has proven difficult.

Cracking the Code

By cracking the genetic code of spider silk, scientists hope not only to be able to duplicate the material but perhaps even to improve on it.

"We're trying to alter both the strength and elasticity of the natural silks," Lewis said. "We've made a number of different synthetic genes based on what we found in natural silks—but altered in ways to make them even stronger and more flexible. We're really trying to control elasticity, so you if come to me and ask for a certain tensile strength and elasticity, I can make a gene that will produce a fiber that does that for you."

Thomas Scheibel, from the department of chemistry at the Technical University of Munich, Germany, is engaged in similar types of "protein engineering." He recently published a review of his work in the journal Microbial Cell Factories.

"We're now not only after the uniqueness of the silk thread but the uniqueness of the single molecular building blocks within that thread," he said.

"We can play around with these modules and try to optimize structures for applications where you need unique specific properties—even those not found in natural silk," Scheibel said.

A range of products could someday ensue.

"I would start with something in the area of paper—paper that's strong, tough, can't be torn. For uses like banknotes silk could be a perfect material," Scheibel said.

"In the aircraft or automobile industry, think about a material that can absorb a lot of energy. If you have an accident [that causes a dent], it might be gone hours later, because the material can take up energy and reacquire its form. That's what happens to a web when an insect flies into the web."

Myriad of Potential Uses

Over hundreds of millions of years the 37,000 known species of spiders (and others unknown) have evolved and diversified many silks for their unique purposes. Best known and studied is silk secreted by a spider's major ampullate glands.

Orb-weaving spiders use this kind of silk like Spider-Man, as a dragline on which to make ascents and descents. The silk is also used to create spiders' familiar "wagon wheel" webs.

Spider silk has incredible tensile strength and is often touted as being several times stronger than steel of the same thickness. What's even more unique, however, is spider silk's elasticity.

"When we say spider silk is tougher than things like Kevlar [a plastic used to make body armor] that's what were talking about. Kevlar has higher tensile strength but it's not very stretchy," said Todd Blackledge, an entomologist at the University of Akron.

These properties suggest a potential for many applications for spider silk: extremely thin sutures for eye or nerve surgery, plasters and other wound covers, artificial ligaments and tendons, textiles for parachutes, protective clothing and body armor, ropes, fishing nets, and so on.

"One that's initially surprising is air bags," Lewis added. "Right now an air bag just sort of blasts you back into a seat. But if it were made out of this material it would actually be made to absorb energy and really reduce impact."

"Spidergoats"

Unlike silkworms, spiders tend to eat one another and cannot be effectively farmed. That's spawned a search for alternative silk sources. The most common method is introducing silk-spider genes into other organisms so that they can produce silk proteins that might later be used to create artificial silk threads. Host organisms range from simple bacteria to goats.

Quebec-based Nexia Biotechnologies created a stir in 2000 when it bred two "spidergoats" named Webster and Pete. The goats were altered with spider genes so that they could produce silk proteins in their milk. Nexia's artificial silk product is known as BioSteel, but the company is currently involved in a restructuring that has stalled research efforts.

Bacteria produce enough proteins for research work, but their long-term commercial production potential is unproven. Other efforts have focused on silk-producing plants such as tobacco or alfalfa and have met with some success.

But while producing spider-silk proteins is becoming more feasible, and scientists continually learn more about how to spin them into solid materials, major hurdles must be cleared before "spider products" become available.

So far, artificial fibers have lacked real spider silk's strength, and the artificial threads have been much wider than their natural counterparts. Before the advent of a spider-silk marketplace, human web weavers must close the technology gap on their arachnid counterparts.

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