When spiders create their webs, they employ their hind legs to pull silk threads from their spinnerets. This action is not just for releasing the silk but also plays a vital role in enhancing the strength of the silk fibers, resulting in more durable webs.
Researchers at Northwestern University have uncovered why this stretching process is crucial. Through computational models simulating spider silk, they found that stretching aligns protein chains within the fibers and increases hydrogen bonds between these chains. Both factors contribute to stronger and tougher fibers.
The research team validated these findings with laboratory experiments using engineered spider silk. The insights gained could be instrumental in designing synthetic materials inspired by silk for various applications, such as biodegradable sutures and high-performance body armor.
The study was published on March 7 in Science Advances. Sinan Keten, the senior author from Northwestern, stated: “Researchers already knew this stretching, or drawing, is necessary for making really strong fibers. But no one necessarily knew why.” He explained that their computational method allowed them to understand nanoscale processes affecting the mechanical properties of silk.
Jacob Graham, the study's first author, added: “Spiders perform the drawing process naturally... We found that you can modify the fiber’s mechanical properties simply through modifying the amount of stretching.”
Keten holds several positions at Northwestern’s McCormick School of Engineering and specializes in bioinspired materials. Graham is a Ph.D. student working under Keten's guidance.
Spider silk has long been admired for its remarkable properties—stronger than steel and tougher than Kevlar—yet farming spiders for natural silk remains challenging. Scientists aim to replicate these qualities synthetically instead.
“Spider silk is the strongest organic fiber,” Graham said. “It also has the advantage of being biodegradable.” He noted its potential use in medical applications due to its harmless degradation within the body.
Fuzhong Zhang from Washington University has been engineering microbes to produce spider-silk materials for years. By manually extruding and stretching engineered proteins, his team developed artificial fibers akin to those spun by golden orb weaver spiders.
Despite progress in creating artificial spider silk, understanding how spinning alters fiber structure remained elusive until now. Keten and Graham used simulations to explore molecular dynamics within Zhang’s artificial silk during stretching.
Their findings showed that stretching causes proteins to align more orderly and increases hydrogen bonds between them—both enhancing strength and elasticity. Experimental tests confirmed these predictions.
Graham remarked on how his perception of spiders changed: “I definitely look at spiders in a new light... I see them as a source of fascination.”
The study titled "Charting the envelope of mechanical properties of synthetic silk fibers through predictive modeling of the drawing process" received support from National Science Foundation grants OIA-2219142 and DMR-2207879.