Stronger than steel, tougher than Kevlar – scientists shed new light on the world’s strongest spider silk

Biophysicist Irina Iashina, University of Southern Denmark, holds silk fibres, produced by a golden web spider. Credit: Anders Boe/University of Southern Denmark

Many scientists aspire to discover the amazing ability of spiders to spin extremely strong, lightweight and flexible silk threads. In fact, spider silk is stronger than steel and tougher than Kevlar. However, no one has been able to replicate the spiders’ work yet.

If we could develop a synthetic equivalent with these properties, it could open up a whole new world of possibilities: synthetic spider silk could replace materials such as Kevlar, polyester and carbon fiber in industries, and could be used, for example, to make lightweight and flexible products. Bullet proof jackets.

Irina Iashina, a postdoctoral researcher and biophysicist from the Department of Biochemistry and Molecular Biology at the University of Southern Denmark (SDU), is participating in this race to uncover the recipe for supersilk. She has been fascinated by spider silk since she was a master’s student at SDU, and is currently researching the topic at the Massachusetts Institute of Technology in Boston with support from the Velome Foundation.

Biophysicist Irina Iashina, University of Southern Denmark, studies spider silk on a computer. Credit: Anders Boe/University of Southern Denmark

As part of her research, she is collaborating with SDU assistant professor and biophysicist Jonathan Brewer, an expert in using different types of microscopes to look at biological structures.

Together they have now, for the first time, studied the interior of spider silk using an optical microscope without cutting or opening the silk in any way. This work has now been published in journals Scientific reports And Scanning is done.

“We used several advanced microscopy techniques, and we also developed a new type of optical microscope that allows us to look at a piece of fiber and see what’s inside,” explains Jonathan Brewer.

The golden orb web spider produces its silk from its hind end. Credit: Anders Boe/University of Southern Denmark

To date, spider silk has been analyzed using different techniques, all of which have provided new insights. However, there were also drawbacks to these techniques, as Jonathan Brewer points out, as they often required cutting the silk thread (also known as the fibre) open to obtain a cross-section for microscopy or freezing samples, which could alter the structure of the silk fibres.

“We wanted to study pure, untreated fibers that have not been cut, frozen, or processed in any way,” says Irina Iashina.

For this purpose, the research duo used less invasive techniques such as Coherent Anti-Stokes Raman Scattering, confocal microscopy, super-resolution fluorescence reflectance confocal microscopy, helium ion scanning microscopy, and helium ion spray.

Various studies have revealed that spider silk fibers consist of at least two outer layers of lipids, i.e. lipids. Behind them, within the fibrils, there are many so-called fibrils that run in a straight arrangement and are tightly packed side by side (see figure). The diameter of the fibrils ranges between 100 and 150, which is less than the limit that can be measured with an ordinary optical microscope.

Illustration from Scientific reports Paper: A schematic (not to scale) representation of the proposed structure of spider silk fibers as found in the present work. (A) Fiber side view, (B) Cross section through the fiber. A non-conductive lipid-rich outer layer (green) 0.6 to 1 µm thick, and two inner conductive layers of autofluorescent protein: one showing higher affinity toward FITC (blue), and another rhodamine B showing higher affinity toward (orange). The inner protein core consists of crystalline fibers, aligned parallel to the long axis of the fiber, surrounded by amorphous protein regions. Source: Iachina/Brewer, University of Southern Denmark.

“It’s not twisted, which one might have imagined, so we now know that there’s no need to twist it when trying to make artificial spider silk,” says Irina Iashina.

Iachina and Brewer work with silk fibers from the golden orb-web spider, Nephila madagascariensis, which produces two different types of silk: one, called MAS (major ampullary silk fibre), is used to build the spider’s web, and is also the silk that the spider uses to cling to. Irina Iashina refers to it as the lifeblood of the spider. It is very strong and is about 10 micrometers in diameter.

The other, called MiS (micro ampullary silk fibres), serves as a building aid. It is more flexible and usually has a diameter of 5 micrometers.

According to binary analysis, MAS silk contains fibrils with a diameter of about 145 nm. As for MiS, it is about 116 nm. Each fiber is made up of proteins, and several different proteins are involved. These proteins are produced by the spider when it makes its silk fibers.

Understanding how such strong fibers are created is important, but producing the fibers is also challenging. Therefore, researchers in this field often rely on spiders to produce their silk.

Instead, they can resort to computational methods, which is what Irina Iashina is currently working on Massachusetts Institute of Technology: “Right now, I’m running a computer simulation of how proteins turn into silk. The goal is of course to learn how to produce artificial spider silk, but I’m also interested in contributing to a greater understanding of the world around us.”

References: “Nanoscopic imaging of primary and secondary ampullae silk from the orb-web spider Nephila Madagascariensis” by Irina Iachina, Jacek Wiotowski, Horst Günter Ruban, Fritz Vollrath, and Jonathan R. Breuer, 24 April 2023, Scientific reports.
doi: 10.1038/s41598-023-33839-z

“Helium ion microscopy and spider silk sectioning” by Irina Iashina, Jonathan R. Breuer, Horst Günter Ruban, and Jacek Wojtowski, May 22, 2023, Scanning is done.
doi: 10.1155/2023/2936788