Spiders spin their silk from proteins and promises. The fibers are tough, flexible and environmentally friendly, and entrepreneurs and scientists imagine they are woven into a variety of products: spider silk, pullovers or even footbridges.
To get there, experts need to find out what's in the stuff. A study published on Monday in the Proceedings of the National Academy of Sciences shows the building blocks of these fibers in the glands of black widow spiders, Latrodectus hesperus .
The researchers observed that protein clumps never attach to previous complex structures. They are tiny aggregates, some with a diameter of no more than 200 nanometers. But when spiders push these teensy globs through their faucet-head-like jets, called spinnerets, at the base of their lower abdomen, the lumps become fibers that stretch foot by foot.
"Spider silk materials are better than any other polymers we have in terms of their material properties," said Gregory Holland, an analytical chemist at San Diego State University and one of the authors of the new report. These materials are "fully biodegradable" and have the potential to replace plastic "anywhere you see it".
Spider silk pendants have been trying for a long time to bind the spider to the spinning wheel. Pounds of spider silk loops are tougher than Kevlar, the material in bulletproof jackets. The problem is scale. An 11-foot spider silk tapestry unveiled in New York's American Museum of Natural History in 2009 took four years, 80 weavers in Madagascar, a million golden orb spiders, and about $ 500,000. In the early 2000s, a company bred transgenic goats that produced silk in their milk. He failed to deliver a consumer product and went bankrupt in 2009 (most of the spider herds were farmed at the University of Utah farm.)
Holland has been working with black widow spiders for years and says their silk is one of them is strongest, even among spiders. Despite the deadly reputation of black widows, the shy animals did not bite any of the 200 scientists and students who passed his lab, he said. Holland has 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 spider silk. The dot in the middle was a mystery. "There is this space between this knowledge and when we see a spider web," Gianneschi said.
Together, the scientists and their colleagues studied the silk proteins in the guts of the black widow before they became fibers. Gianneschi and Holland attributed much of the labor-intensive imaging work to two researchers, Lucas Parent of Northwestern and David Onofrei of SDSU.
Holland is concerned with spider silk on an atomic-by-atom basis using a technique called nuclear magnetic resonance or NMR – the same principle behind an MRI machine. Gianneschi's laboratory uses cryo-electron microscopy. Large molecules suspended in the liquid are flash frozen in place. This keeps the molecules and their natural shape intact while scientists scan the samples with ultra-high microscopes. (Three biophysicists won the 2017 Nobel Prize in Chemistry for the development of cryo-electron microscopy.)
This work combines the two techniques. "We make sure what we see at room temperature in NMR and what he sees after freezing, it tells us the same," said Holland.
Researchers Predicted That Silk Proteins Float Free in the Water Spider glands might clump into bubbles called micelles. The authors of the new report found something more complex. They described the structures as "nanoscale hierarchical arrangements". In other words, they found blisters as predicted, but the blisters had clumped in unexpected ways.
Nature always uses hierarchical arrangements. Gianneschi offered a simplified example: "It would be almost like looking at a single petal on a flower, the individual petals have structure, and they are very interesting to themselves, but when we see them in nature, we see it as an arrangement. "If a micelle was a petal, the assembly was the flower.
The chain of events goes something like this: A spider eats prey and digests its food in the most elementary parts, the amino acids. The spider builds these amino acids into proteins, builds proteins into micelles, micelles into aggregates and builds them into fibers and webs. And this process is reversible – spiders can eat their own nets and reuse the same amino acids in new silk strands.
Currently, researchers can synthesize spider silk proteins that are purified to a powder. These proteins are mixed with liquid, such as by adding water to a cake mix. The trick is to spin the protein dough into fibers as strong as a spider's.
In early 2017, a research team announced that it had created a process for spinning long artificial spider silk fibers. The technique could produce strands of one kilometer in length. Janne Johansson and Anna Rising, scientists at the Karolinska Institute in Sweden, who helped develop the method, wrote a joint statement to the Washington Post to evaluate the study published this week: "This study paints a more detailed picture of like spider silk proteins "go from a dissolved substance in the glands to a fiber, said Johansson and Rising.
Even with this study, scientists will not be able to produce better spider silk tomorrow. "But it will definitely provide models that will allow the research community to come up with new hypotheses for designing [spider proteins] in the lab, and how to handle and rotate it," said Johansson and Rising.
The new report may provide guidance on how to improve artificial egg whites. The authors of the study plan to work with the people who made synthetic spider silk protein powders to make sure that the nano-assemblies appear on the target. "We have just opened a new door to explore," said Holland.
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