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September 3, 2001
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Spider Engineering
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They live life
on the edge. They're hanging on by a thread. They'll jump
off a building without flinching. The strongest spider silk, made by the golden silk spider, Nephila, is the strongest fiber known to man! It is five times as strong as steel. It is also stronger and more elastic than Kevlar, the patented material used in bullet-proof vests. Spiders make silk using a system of silk glands in their abdomens. The silk is mostly made up of the proteins fibroin and sericin. (Another natural fiber that is made up of protein is your hair — but it is made of the protein keratin.) Scientists understand a lot about the protein molecules in spider silk, but they're not sure how the silk is constructed because strands of spider silk are so tiny. A single strand that measures 3-5 microns across may be made up of thousands of individual sub-strands that are too small to be examined by any microscope. (A micron is equal to one millionth of a meter, or one thousandth of a millimeter.) Because of its size, and the complex way spiders create the silk, it's a real challenge for humans to replicate. |
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Webs of Delicate Strength For such fragile-looking structures, spider webs are strong. You'll know this if you have ever watched a web flexing in the breeze or withstanding the impact of an insect. Imagine a fly whizzing into a web. Why doesn't the web snap on impact? It's because the web is highly elastic. The golden silk spider's web is actually strong enough to stop a small bird in flight! This type of spider web is known as an "orb web." It is built by several spider families. The web may only be up for one day, and throughout the day, the spider repairs the web as necessary. Not all spiders weave webs, but of those that do, the most impressive is the golden silk spider: Its web can measure up to three feet in diameter! |
Why Copy Spider Silk? The benefits of humans being able to generate spider silk are immense. Imagine building a suspension bridge with suspension cables that are modeled on the structure of spider silk. The cables would be stronger and more elastic, and would therefore have a much greater chance of withstanding earthquakes. Imagine car bumpers made of similar stuff — instead of denting, they would absorb impacts like a spider web, and simply bounce back to their original shape! Aircraft construction could also benefit greatly from a resistant and flexible material like spider silk. There is even talk of using spider silk for surgical sutures.
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Spider Farms? Goats, Bacteria, and Potatoes Scientists are faced with two challenges: (1) to build the same proteins that a spider produces for its silk, and (2) to construct silk fibers the same way a spider does. To address the first challenge, scientists have been trying to find ways of manipulating other organisms to encourage them to produce the same molecules that are found in spider silk. To that end, they are experimenting with goats, bacteria, and potatoes! If scientists prove successful, these organisms would become living factories of spider silk proteins. A spider's genes contain the instructions for making spider silk proteins. By inserting the correct spider genes into other organisms, scientists hope they can get them to produce spider silk proteins along with their own proteins. For example, goats that have been given the spider genes will produce goat's milk that contains spider silk proteins. Potatoes have also been modified to contain the same proteins. As for the second challenge: Scientists are building machines that replicate the process that a spider uses to create silk fiber. But so far, the machines have not been able to replicate the entire process exactly; and they are also far too costly to be scalable (that is, used for large-scale industrial production). The efforts to copy spider silk continue because the benefits of having large quantities of this material available would be so great. So, next time you see a spider in the tub, don't panic. Try taking a closer look and admire this small, creepy genius who holds the secrets of the world's strongest material! |
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