Spiders spin their silk out of proteins and promise. The fibers are tough, flexible and environmentally friendly, and entrepreneurs and scientists envision them woven into a host of products: spider silk sutures, sweaters or even footbridges.
To get there, experts have to figure out what’s in the stuff. A study published Monday in the Proceedings of the National Academy of Sciences reveals the building blocks of these fibers within the glands of black widow spiders, Latrodectus hesperus.
The researchers observed that globs of proteins aggregate into never-before-seen complex structures. They’re tiny aggregations, some no more than 200 nanometers in diameter. But when spiders squeeze these teensy globs through their faucet-head-like nozzles, called spinnerets, at the base of their abdomen, the clumps become fibers that stretch for foot after foot.
“Spider silk materials are better than any of the polymers we have in terms of their material properties,” said Gregory Holland, an analytical chemist at San Diego State University and one of the authors of the new report. These materials are “completely biodegradable,” he said, and have the potential to replace plastic “any place you see it.”
Spider silk devotees have long tried to yoke the spider to the spinning wheel. Pound for pound, loops of spider silk are tougher than Kevlar, the material in bulletproof jackets. The trouble is scale. An 11-foot spider silk tapestry, unveiled at New York’s American Museum of Natural History in 2009, required four years, 80 weavers in Madagascar, a million golden orb spiders and about $500,000.
Holland has worked with black widow spiders for years, and he considers their silk to be some of the strongest, even among spiders. Despite the black widows’ deadly reputation, the shy animals have not bitten any of the 200-some scientists and students who have passed through his lab, he said. Holland recently teamed up with Northwestern University’s Nathan Gianneschi, who uses electron microscopes to study nanomaterials.
Scientists knew the makeup of the individual protein molecules in silk. And you and I can see the long strands of spider silk. The spot in the middle was a mystery. “There’s this space between that knowledge and when we see a spider web,” Gianneschi said.
Together, the scientists and their colleagues used advanced imagery techniques to examine the silk proteins, before they became fibers, within the black widow guts. Gianneschi and Holland credited two research scientists, Northwestern’s Lucas Parent and David Onofrei at SDSU, with much of the imaging work.
Holland deals with spider silk on an “atom-by-atom” basis, using a technique called nuclear magnetic resonance, or NMR — the same principle behind an MRI machine. Gianneschi’s lab uses cryo-electron microscopy. Large molecules suspended in liquid are flash-frozen in place. This keeps the molecules and their natural shape intact while scientists scan the samples with ultrapowerful microscopes.
