When you stretch your spider silk, it becomes stronger by aligning the protein chains.

As the spider rotates the net, it uses its hind legs to pull the silk thread from the spinet. This pull action not only helps spiders release silk, but it is also an important step in strengthening silk fiber for a more durable web.

In a new study, researchers at Northwestern University discovered why the role of stretching is so important. By simulating Spider Silk in a computational model, the team discovered that the stretching process aligns the protein chains within the fibers and increases the number of bonds between those chains. Both factors lead to stronger and more durable fibers.

The team then validated these computational predictions through laboratory experiments using designed spider silk. These insights help researchers design engineered silk-inspired proteins and design spinning processes for a variety of applications, including powerful, biodegradable sutures and sturdy, high-performance explosive body armors.

This research is published in Science Advances.

“The researchers already knew that this stretch, or drawing, was necessary to create truly strong fibers,” said Sinan Keten of Northwestern, a senior author of the study. “But no one necessarily knew why. The calculation methodology allowed us to investigate what was happening on the nanoscale and gain insights that we wouldn’t see experimentally.

“The spiders naturally carry out the drawing process,” said Jacob Graham, a Northwestern researcher, the first author of the study. “When they spin the silk out of the silk glands, the spider uses its hind legs to grab and pull the fibers out. It stretches when the fibers are formed. It makes the fibers very strong and resilient.

Keten is a bioinspired material expert, Professor Jerome B. Cohen of Engineering, Professor of Mechanical Engineering, and Professor of Civil and Environmental Engineering at the McCormick School of Engineering, Northwestern. Graham is a PhD. A student in the Keten research group.

Stronger than steel, stronger than Kevlar

Researchers have long been interested in Spider Silk because of its incredible properties. It’s a rubber that’s stronger than steel, stronger than Kevlar, and more elastic. However, natural silk farming spiders are expensive, energy intensive and difficult. So instead, scientists want to replicate silky materials in their labs.

“Spider silk is the most powerful organic fiber,” Graham said. “It also has the advantage of being biodegradable. Therefore, it is an ideal material for medical applications. It can be used for surgical sutures and adhesive gels for wound closure, as it naturally deteriorates harmlessly within the body.”

Huzn Chan, co-author of Huzn Chan, professor F. Erman at Washington University in St. Louis, is an engineering microorganism for producing spider silk materials for several years. By pushing out engineered spider silk proteins and stretching them out by hand, the team developed artificial fibers that resemble the threads of Golden Silk Orb Weaver, a large spider with an epic powerful web.

Elasticity simulation

Despite developing this “recipe” for Spider Silk, researchers still don’t fully understand how the spinning process changes the structure and strength of the fiber. To address this open-ended question, Keten and Graham developed a computational model to simulate the molecular dynamics within Zhang’s artificial silk.

Through these simulations, the Northwestern team investigated how stretching affects the placement of proteins within the fibers. Specifically, we investigated how protein order, protein connections with each other and how molecules can be extended within the fibers change.

Keten and Graham discovered that the proteins were lined up through stretching, increasing the overall strength of the fiber. They also found that stretching increases the number of hydrogen bonds that act like bridges between protein chains to form the fibers. Increased hydrogen bonding contributes to the overall strength, toughness and elasticity of the fiber, the researchers found.

“When a fiber is extruded, its mechanical properties are actually very weak,” Graham said. “But when it grows to six times the initial length, it becomes very strong.”

Experimental verification

To verify the computational findings, the team used spectroscopic techniques to examine how protein chains were extended and aligned in the actual fibers of the Washu team. We also used tensile tests to see how much elongation the fibers could tolerate. The experimental results were consistent with the simulation predictions.

“If you don’t stretch the material, you’ll have these spherical swarms of protein,” Graham said. “But stretching turns these spheres into interconnected networks. The protein chains stack together, and the networks become increasingly interconnected. The bundled proteins can elucidate more and more and more before the fiber breakage, but the proteins that were first expanded will become less extensible fibers that require more force to be cut.”

Graham once thought Spiders were creepy crawleys, but he now sees their potential to solve the real problem. He points out that engineered spider silk offers a stronger, biodegradable alternative to other synthetic materials, mostly petroleum-derived plastics.

“I’m definitely watching a spider in a new light,” Graham said. “I used to think it was a nuisance. Now I see them as a source of appeal.”