The secret of super-strong canvases lies in the tiny structures of spider glands

Spiders spin their protein silk and promise. Fibers are strong, flexible and environmentally friendly, and contractors and scientists consider them in a multitude of products: spider silk sutures, sweaters or even footbridges.

To achieve this, the experts must understand what is in the material. A study published Monday in the Proceedings of the National Academy of Sciences reveals the building blocks of these fibers in the glandular spider glands of black widows, Latrodectus hesperus.

Researchers have observed that protein globules aggregate into complex structures never seen before. These are tiny aggregations, some of which do not exceed 200 nanometers in diameter. But when the spiders press these tiny globules by their faucet-shaped nozzles, called dies, located at the base of their abdomen, the tufts become fibers that stretch out foot by foot.

"The spider silk materials are better than all the polymers we have in terms of material properties," said Gregory Holland, analytical chemist at San Diego State University and one of the authors of the new report . These materials are "completely biodegradable", he said, and have the potential to replace plastic "wherever you see it".

Adepts of spider silk have long tried to associate the spider with the spinning wheel. Pound for pound, spider silk curls are stronger than Kevlar, the material of bulletproof vests. The problem is the scale. An 11 foot spider silk tapestry, unveiled at the American Museum of Natural History in New York in 2009, required four years, 80 weavers in Madagascar, a million spiders from around the world. golden orbs and about $ 500,000. In the early 2000s, a company raised transgenic goats that produced silk in their milk. It failed to deliver a consumer product and went bankrupt in 2009 (most of the flock of spider goats were liquidated at the University of Utah farm).

Holland has been working with black widow spiders for years and considers that their silk is one of the strongest, even among spiders. Despite the murderous reputation of black widows, shy animals did not bite any of the more than 200 scientists and students who passed through his laboratory, he said. Holland recently teamed up with Nathan Gianneschi of Northwestern University, who uses electron microscopes to study nanomaterials.

Scientists knew the composition of individual protein molecules in silk. And you and I can see the long strands of spider silk. The spot in the middle was a mystery. "There is this gap between this knowledge and when we see a spider's web," Gianneschi said.

Together, scientists and their colleagues used advanced imaging techniques to examine silk proteins before they became fibers in the bowels of the black widow. Gianneschi and Holland have awarded research to two researchers, Lucas Parent and David Onofrei from the North West at SDSU, with much of the labor-intensive imaging work.

Holland treats spider silk on an "atom-by-atom" basis, using a technique called nuclear magnetic resonance, or NMR – the same principle used by an MRI machine. Gianneschi's laboratory uses cryo-electronic microscopy. Large molecules suspended in the liquid are frozen on site. This allows the molecules and their natural form to remain intact while the scientists analyze the samples with ultra-powerful microscopes. (Three biophysicists won the 2017 Nobel Prize in Chemistry for the development of cryo-electronic microscopy.)

This work connected the two techniques. "We make sure that what we see at room temperature in the NMR and what it sees after quick freezing, it tells us the same thing," Holland said.

The researchers predicted that silk proteins floating freely in the spider glands could clump into bubbles called micelles. The authors of the new report found something more complex. They described the structures as "hierarchical assemblages at the nanoscale". In other words, they found bubbles, as expected, but the bubbles were unexpectedly grouped together.

Nature uses hierarchical assemblies all the time. Gianneschi proposed a simplified example: "It would be almost like looking at a single petal on a flower. Individual petals have a structure and are very interesting in themselves, but when we see them in nature, we consider them as a whole. If a micelle was a petal, the assembly was its flower.

The chain of events then looks like this: a spider eats its prey and digests its meal into basic elements, the amino acids. The spider builds these amino acids into proteins, proteins into micelles, micelles into assemblages and assemblages into fibers and webs. And this process is reversible – spiders can eat their own webs and reuse the same amino acids in new silk threads.

Currently, researchers can synthesize spider silk proteins, which are purified to powder. These proteins are mixed with a liquid, such as to add water to the cake mix. The trick is to turn the protein paste into fibers as strong as a spider.

In early 2017, a team of researchers announced that she had created a process for spinning long artificial spider silk fibers. The technique could produce strands of one kilometer long. Janne Johansson and Anna Rising, scientists at the Karolinska Institute in Sweden, who contributed to the development of the method, wrote a joint statement to the Washington Post to evaluate research published this week: detailed how spider silk proteins "go from a substance dissolved in the glands to a fiber," said Johansson and Rising.

Even with this study, scientists will not be able to create better spider silk tomorrow. "But it will certainly provide models that the research community can now use to formulate new hypotheses about how to design [spider proteins] that can be produced in the laboratory and how to treat and spin them, "said Johansson and Rising.

The new report potentially offers tips on how to improve artificial protein pulp. The authors of the study intend to collaborate with the people who made synthetic spider silk protein powders to check if the nano-assemblages appear in the spreadsheet. "We have just opened a new door to explore," Holland said.

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