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Brown Recluse Silk Is Stronger Than Steel Because It’s Constructed Like a Cable

Thousands of nanotendrils come together to form the flat, super-strong spider silk

(Wikimedia Commons)
smithsonian.com

Spider silk is often touted as some of the strongest material on Earth: According to some calculations, it can be up to five times stronger than steel cable of similar weight—though that comparison is not perfect. If humans could manufacture spider silk on an industrial scale, which they’ve been trying to do for decades, it could lead to an era of lightweight bulletproof vests, helmets, superstrong threads and patches that could be used during surgery and even lightweight airplane fuselages. One major problem, however, is that scientists don’t know exactly what makes spider silk so strong and stretchy. Recent studies, however, are beginning to unravel the mystery.

One reason spider silk has been difficult to figure out is that the strands of silk are super thin and getting a good look at the cylindrical threads under a microscope is difficult. Courtney Miceli at Science reports that’s why researchers at the College of William & Mary have concentrated on silk from the brown recluse spider, which produces a flat ribbon that is easier to examine using atomic force microscopy to look at the strands at the molecular level. That level of detail is necessary—the silk strands can be as tiny as 1/1000th the size of a human hair.

In their latest study in the journal ACS Macro Letters, the team found that instead of being one long strand of protein, the ribbon of silk is composed entirely of 1 micron-long nanostrands stuck together in parallel. Typically, about 2,500 of these mini-strands clung together to form one strand of silk.

“We were expecting to find that the fiber was a single mass,” co-author Hannes Schniepp of William & Mary says in a statement. “But what we found was that the silk was actually a kind of tiny cable.”

This isn't the team's first silken discovery either. In a 2017 study, they looked closely at how the little arachnids spin their silk, finding that they create tiny loops which add toughess to the fibers. Each strand has up to 500 loops per inch. Miceli reports that previous studies had proposed that nanostrands were involved in the makeup of the silk, but no one had considered that the entire strand would be composed of them. Armed with the new research and information about the loops, the researchers have now created a new model for the spider silk’s structure. The nanotendrils aren't braided together like in a rope cable, but are instead stuck together with relativley weak bonds. When they act as a whole, however, the strands give the silk its incredible strength.

Another study published in late October is also helping researchers make sense of spider silk. Scientists examining black widow spiders have figured out the complex process that transforms amino acids, the raw material for the webs, into actual spider silk. Using state of the art microscopy, researchers were able to watch how the spider's silk glands assemble the proteins into silk strands, a process that could help human spinners figure out more efficient ways of producing spider silk for commercial use.

While several companies in recent years have announced plans to bring spider silk products to market and introduced prototypes, including shoes and jackets made from the stuff, we’ve yet to see any arachno-clothing at the local mall.

About Jason Daley

Jason Daley is a Madison, Wisconsin-based writer specializing in natural history, science, travel, and the environment. His work has appeared in Discover, Popular Science, Outside, Men’s Journal, and other magazines.

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