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Spiders: feared by some, their silk is nevertheless about 5 times stronger than steel, making them very interesting in our quest to engineer cheap, strong materials. This week, scientists have put one of America's most dangerous spiders under the microscope to discover the secret of how it makes its particularly strong web. They discovered that, by adding little loops, it can make a strong and stretchy material that's much less likely to break under under stress. Using the same technique, we could engineer super tough, flexible materials in the future. Georgia Mills spoke to Hannes Schniepp from The College of William and Mary in Virginia...
Hannes - The specific spider we're working with is the brown recluse spider, which is actually quite infamous in the United States because it has a very bad bite and it has a quite dangerous venom. So a lot of people in the United States know about the brown recluse spider but we'd actually like to feature some of it's really interesting properties. The silk of most spiders they're really cylindrical just like a hair, but the silk of the brown recluse spider, if you look at it under the microscope,it just looks like a piece of sticky tape. This flat ribbon shape allows the spider to take this silk and form it into loops and these loops make the material extraordinarily tough, and that makes it a better material for the spider in order to capture prey.
Georgia - Why would loops make it tougher?
Hannes - Yeah. That's really the very interesting thing and very puzzling. What actually happens is that first of all because the silk is so sticky these loops that the spider makes, they're closed loops and they have relatively strong loop junctions or joints. And if you start pulling on the material, at some point these loops can actually open and release some additional links of the material. So that means you start stretching the material, and as soon as you reach the critical force that's required to open one of the loops, the link that's stored in this loop is released and then the silk fibre is relaxed a little bit. Then you stretch it again until the next loop opens and so on and so on, and in the process you stretch and release the material many, many times and that is something that takes a lot of energy, and that's what we material scientists call 'toughness.'
Georgia - Oh wow! So then the poor fly, or whatever it is they eat, it's got so many loops to break as it were. It's just going to take too much energy to actually cut through one of these fibres.
Hannes - That is correct. Isn't that absolutely fascinating? We sometimes think of it as the ultimate barbed wire. So you have an incredibly sticky material which is, at the same time, also one of the strongest materials that we have. So if a poor little creature gets stuck in there there's no way out.
Georgia - Oh dear! Can we take this? What kind of applications could this tough material have?
Hannes - For instance, if you think like if you're jumping down and you wear a parachute, and you want to open the parachute and, at the moment, when you open there's an enormous amount force that goes into the cord that holds the parachute. So there we could use a material that has such loops built in to make it a little bit more stretchier and better at absorbing the energy without breaking.
We've also thought about to protect structures from impact - let's say weapons - that might be useful, or you could think about if you have a structure in space where you have space debris or micro meteorites flying around at very high velocities. You could think about making a web of such material around these structures to protect them from such high energy objects.
Georgia - I love that image of a spider's web in space hoovering up all the meteors and things. Spider's silk is incredible but it is, as you mentioned, tiny. Do you think it's going to be feasible to scale this up to such an extent that it's actually useful to us?
Hannes - Well, in a way, we actually scaled this up and because we were so fascinated by this we thought wow, is this real because it's so surprising that this works. We also developed mathematical models to simulate the kind of energy gains that we would get from a material like this. And the first thing we did was we just went to the drawer in our lab and took a piece of sticky tape and then we just manually put a loop into the sticky tape, and then we tested this tape as you test any material. We put it in a mechanical tester and we measured the energy that it takes to break this material and we indeed found out that, even with one single loop, we increased the energy that this can absorb by about 30 percent, which is totally in line with our predictions. So that means if we find out a way to have many loops in there we could actually increase the toughness, or the ability of the material to absorb energy tremendously. And with this simple example, you can see it does not necessarily have to be at the micro or nano scale to make this work.
Toughness-enhancing metastructure in the recluse spider's looped ribbon silk - DOI: 10.1039/C6MH00473C
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Permalink Submitted by Heather (not verified) on Tue, 14/03/2017 - 02:53
I am guessing this guy is not a knitter even though the spider clearly is. Knitted material is made up of interlocking loops, just as described, making the fabric stronger and flexible. So he just discovered a centuries old craft to make strong, durable, flexible material called...knitting.
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