William & Mary: W&M study reveals novel findings on internal structure of spider silk

New research by W&M scientists has unraveled mysteries behind one of the world’s most elusive materials: spider silk. Their findings, recently published in the journal Nature Communications, reveal the internal, hierarchical structure of spider silk fibers in unprecedented detail. The research provides scientists the clearest picture yet of a material that has long been studied for its engineering potential.

The strength and toughness of spider silk makes synthetic spider silk something of a “holy grail” in materials science and engineering. A strand of spider silk is five times stronger than a steel cable of the same weight, explained Hannes Schniepp of the Department of Applied Science at William & Mary, who is lead author of the study.

“Scientists all over the world have studied spider silk because it is so incredibly strong,” Schniepp said. “It is also flexible. It’s tough. So, it’s a material stronger than steel with ten times the extensibility of a material like Kevlar. It just has incredible potential.”

The team of W&M researchers used the silk of recluse spiders to develop a highly detailed structural model, featuring seven levels of structural hierarchy, revealing the composition of microscopic fibers (or nanofibrils) within spider silk and providing the best picture yet of the silk’s structural makeup.

“Spider silk combines high strength and large extensibility with low density and is one of the most appealing materials found in nature,” the researchers write. “Nanofibrils have long been suspected to play a pivotal role within the intricate, hierarchical silk structure of the protein fibers. Surprisingly little, however, is still known about these silk nanofibrils, despite increased recent attention.”

The researchers, all from various departments within William & Mary, used an extremely sensitive technique known as atomic force microscopy and combined it with nuclear magnetic resonance to examine the internal structure of the spider silk at the molecular level. The paper’s coauthors are: Qijue Wang, Patrick McArdle, Stephanie Wang, Ryan Wilmington, Zhen Xing, Alexander Greenwood, Myriam Cotten and Mumtaz Qazilbash.

William & Mary Ph.D candidates in Applied Science Dinidu Perera and Ben Skopic ’20 feed a cricket to a male recluse spider within the lab.
Schniepp explained that the novel approach they developed for studying silk is directly applicable to other proteinaceous materials as well.

“The silk is a protein material,” Schniepp said. “And what these spiders do with it is incredible. They start with a protein and end up with something that’s stronger than steel. The techniques that we developed to study the nanofibrils of spider silk could be applied to study any protein. We could determine the structure of collagen, for example, with a similar level of detail based on the techniques that we developed in this work.”

The team’s findings may have big implications for the future of science and engineering, but the scale of their work is extremely small. A single nanofibril is about 10,000 times smaller than the size of a human hair, Schniepp explained.

“Most spider silks are cylindrical in shape, like a rope,” Schniepp said. “But the recluse spider produces a very unique type of silk. It’s like a thin, flat ribbon that functions more like a cable, which means that the fiber is actually made stronger by its internal structure, by the smaller nanofibrils inside.”

The researchers state that, in combination with available mechanical property data for spider silk, the new wealth of structural data they discovered will provide new opportunities to develop more rigorous structure analysis of spider silk – and ultimately guide the development of high-performance synthetic fibers inspired by spider silk.

“Right now, we’re innovating and discovering in tiny steps, but there’s the larger goal of fully understanding the structure of spider silk,” Schniepp said. “This study solves a piece of that puzzle and takes us closer to the larger dream of one day making materials like nature and, in doing so, create a more sustainable world.”