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Super fibers: Spinning spider webs without spiders
  

 

The silk fibers in spider webs have for decades inspired scientists to create imitations in the laboratory. But the imitations rarely approach the standard: Spider silk is stronger than many high-performance synthetic fibers and has greater elasticity. Now, a team has transferred spider genes into mammalian cells and generated fibers that have some of the properties of natural silk. The fibers are biodegradable and could be used as sutures for surgeries, for example.


Scanning electron micrographs of an ADF-3 as-spun fiber. (A) Analysis of fiber surface (magnification, x500); (B) analysis at a break point to examine the fiber interior core (x2000).

The researchers mimicked the spider’s silk-production process in a controlled environment. They started by transferring two genes for silk from different spider species into mammalian cells. After the proteins were expressed and isolated in sufficient quantities, they were spun into fibers that resembled natural silk in its weight, strength and elasticity.

The proteins (ADF-3/MaSpII and MaSpI) are found in ‘dragline’ silk—the fibers in the spider’s safety line and the radiating spokes of a spider web. Dragline silk has a combination of strength and toughness unmatched by high-performance synthetic fibers; it is five times stronger by weight than steel. Some spiders produce up to seven distinct types of silk, each with different mechanical properties and functions.


ADF-3 fiber spun from a 22% (w/v) rc-spider silk protein solution in methanol, then drawn fourfold in methanol and once in water. The fiber was observed under polarizing light with a 530-nm first-order red plate. Areas of elongation are apparent after the fiber has undergone mechanical testing.

The mechanical properties of silk fibers are determined largely by the conditions under which they are spun and processed. Unlike some earlier efforts, the researchers spun the silk without strong chemical solvents. To mimic the water-based solution in a spider’s silk gland, the researchers expressed the proteins in cells (from cows and baby hamsters).

Anthoula Lazaris and Costas Karatzas, of Nexia Biotechnologies near Montreal, Canada, led the study. “These fibers could be used in a variety of applications: for example, as very fine monofilament sutures in microsurgery or in uses requiring a high level of energy absorption and elongation similar to that provided by Nylon,” the researchers write in Science.

The team included members of the U.S. Army Soldier Biological Chemical Command in Natick, Massachusetts, who provided expertise in spinning the proteins into silk.

“This approach provides a path forward that should lead to the duplication of the silk’s native mechanical properties in an environmentally compatible process,” writes David L. Kaplan of Tufts University in Medford, Massachusetts, in a commentary this month in Nature Biotechnology. The technical barriers that remain relate to optimizing the process and scale, he adds.

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Kaplan, D.L. Spiderless spider webs. Nat Biotechnol 20, 239-240 (March 2002).
 
Lazaris, A. et al. Spider silk fibers spun from soluble recombinant silk produced in mammalian cells. Science 295, 472-476 (January 18, 2002).
 

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