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Man-Made Silk Fibers Hold Great Promise for Military, Medicine

Thursday, 17 January 2002 12:00 AM

Researchers hope the silk from transgenic goats soon will find use in medical and military applications, anything from artificial tendons to bulletproof vests.

"Mimicking spider silk properties has been the holy grail of material science for a long time," said geneticist Jeffrey Turner, president of Nexia Biotechnologies in Montreal, the entrepreneurs that developed the artificial silk. "Now we've been able to make useful fibers."

Spider silk is a unique combination of strength, lightness and toughness unmatched by high-performance synthetic fibers. It is environmentally friendly and biodegradable to boot. Five times stronger by weight than steel, researchers have been trying to harvest spider silk for decades.

"It's incredible such a tiny animal found literally in your backyard can create such an amazing material by using only amino acids, the same building blocks that are used to make skin and hair," Turner said.

"Spider silk is a material science wonder, a self-assembling, biodegradable, high-performance, nanofiber structure one-tenth the width of a human hair that can stop a bee traveling at 20 miles per hour without breaking. Spider silk has dwarfed man's achievements in material science to date."

Attempts to harvest silk from spider farms has proven impractical because the aggressive, territorial nature of spiders makes them difficult to domesticate. Spider silk proteins have been produced in genetically engineered bacteria and yeast with only limited success. The microbes appear to snip the silk genes short because of the highly repetitive nature of the DNA in the genes, leading to shorter, inadequate silk proteins.

Researchers at Nexia, working with the U.S. Army Soldier Biological Chemical Compound in Natick, Mass., tried splicing spider silk genes into two types of mammal cells that more closely mimic the glands spiders use to secrete silk: cow mammary gland cells and baby hamster kidney cells. The silk genes used are from two species of orb-web weaving spiders and encode for the dragline silks the spiders use in their safety lines and the radiating spokes of their webs, silk that is among the strongest reported.

The spider-mammal cells made silk proteins the scientists purified out and spun into fibers with a prototype spinning apparatus that uses tubes no wider than a human hair, "mimicking the spider's way of spinning silk, a process that has been perfected through 400 million years of evolution," said molecular biologist Costas Karatzas, a lead researchers behind the silk and vice president of research and development at Nexia.

The spinning process relies only on a water-based solution, which is "considerably more environmentally friendly than using harsh solvents, such as those used for most synthetic fiber manufacturing," Karatzas added.

The artificial fibers are similar to natural silk but slightly less strong due in part to the spinning methods Nexia used, said polymer physicist Michael Ellison at Clemson University in South Carolina, whose team is working on generating modified silk fibers from genetically engineered plants.

"We're trying to purify and concentrate while the polymer is flowing through the duct," Ellison said in an interview with United Press International. "The spider has many more processes involved than simply spinning it out."

Ellison added, however, the researchers' new results were an important piece of work. "They have helped understand some of the vexing issues in molecular biology," he noted.

The researchers have developed transgenic goats to make silk in their milk. The goats should begin producing silk-laden milk later this year, Nexia said.

By modifying the silk genes and varying the spinning parameters, the researchers hope in the future to get fibers with a wide range of tailored qualities. The silk may find uses in anything from fishing lines to medical sutures in microsurgery on the eyes or nerves.

The researchers reported their results in Science magazine. Copyright 2002 by United Press International.

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Researchers hope the silk from transgenic goats soon will find use in medical and military applications, anything from artificial tendons to bulletproof vests. Mimicking spider silk properties has been the holy grail of material science for a long time, said geneticist...
Thursday, 17 January 2002 12:00 AM
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