Can we copy spider silk?
Spiders are one of the most promising creatures for biomimicry. And that's because they produce different types of silk - some super sticky, some super strong, and others, super stretchy. The closest we've come to artificially recreating the characteristics of spider silk is something called aramid which is used in bulletproof vests and bicycle tires. But to make this fibre requires high temperatures and pressures which means the process is polluting, expensive, and inefficient. But a spider can make it at room temperature on a diet of dead flies and water so how do they do it? Graihagh Jackson went to the Rutherford Appleton Laboratory in Oxfordshire to speak to Ann Terry...
Ann - Spider silk is remarkable because it's actually the toughest material we know. So that means that it's not just strong, but it's also very elastic. And in that way, it's able to absorb all the energy. If you think of a classic spider's web, a spider has to capture the prey as it hits that web. So that means it has to trap it, it has to stop it and if you think some of these flies being caught in webs are so much bigger than the actual fibre that's catching them. And so, it has to damp all of that energy. And so, this means that you end up with a very, very tough material.
Graihagh - So, how does a spider make silk?
Ann - So, the spider produces these proteins in water in its body and then pass through a duct to the exit of the spider's abdomen. Now, a spider doesn't push the silk proteins out to make the fibre. A spider actually pulls them out. So, a spider will glue down the silk that they want to produce and then walk away to draw the silk out. And within its body, what it does is it changes the pH of the solution. It changes the metal ions, and the salts which were involved in giving the protein its shape and how it folds. And at the same time, starting to elongate the molecules and stretch them so they're able to come together to form these closed links they need to actually make a fibre.
Graihagh - I always thought of it as a bit like a spool, like on a sewing machine that pulls it out, but obviously going from a liquid or a gel then to a solid, it's much more complex than that.
Ann - Yeah, so it's actually produced on demand. It's not stored as a reeled up fibre in the body and the spider produces up to seven different types of silk or from different exits, all from different little spineretts and they all have a different chemical constituency. They have a different sequence of amino acids that means, they're produced in very slightly different ways. So, the shape of the storage gland and the duct is different and that leads to different mechanical properties. So, some are highly elastic, some are sticky, some are these super tough fibres. So, in one naturally occurring system, we have the ability to look at all of these ranges of properties.
Graihagh - How do you physically look at them? Are you using a microscope?
Ann - So, we've been using a technique called small-angle neutron scattering. What we're looking at is the actual size and shape of the proteins in the solution and then from that information, we then change in some way the chemical constituency of that solution. We might change its pH, we might change the amount of salt in the solution and then look and see how that has influenced the silk proteins. And all of those things help us to build a picture of how the spider might be controlling the silks in situ in their abdomen.
Graihagh - There's a tiny teeny spider's web next to us on a bench. I'm looking at it and we're all familiar with that feeling when you walk through the garden and you walk into a spider's web, you can sort of feel the lose strings on it. How strong is it?
Ann - To even feel one of the small spider's webs is remarkable. That fibre in that web is at least 20 times thinner than a human hair. If not, more. And so, the webs that we deal with or the spiders that we use are actually what's called the Golden Orb Web Spider. They spin a silk that is so strong that as you put your hand up, it can really resist your hand.
Graihagh - So, where do you keep all these orb spiders?
Ann - So, we have greenhouses. Imagine what these greenhouses are like. Spiders eat flies, so these are greenhouses filled with spiders and flies. So, they're not a particularly nice environment to go into. But we go in and we collect a spider and then we take them down to our lab. And literally, we can immobilise them on a small board and then actually collect the silk from the abdomen by winding iy up onto a mechanical bobbin. Now the beauty of this means we can actually sometimes we reel them very fast, sometimes very slow and look at how the properties change as we do that.
Graihagh - How much silk can you get from one spider?
Ann - We're talking about very, very little silk. So, a female spider can reel hundreds of metres of silk, but it's such a fine fibre. So although you might reel a lot, it's actually not a lot of material.
Graihagh - So, how might we be able to one day hopefully, either - I suppose, manufacture it or produce it somehow synthetically?
Ann - Well, that's being looked at. So, there are groups who are looking at how you could make silk proteins. And so, they will try and put the silk proteins into plants and things like that, but you still need to be able to process them into something useful.
Graihagh - Harnessing something of this power, of this strength surely means there's got to be lots of really interesting applications if we could reproduce something like spider silk.
Ann - Yeah, and a huge range of applications as well. So, everything from applications where you need something very light weight, or you could think of lightweight tethers for space applications, right through to - there's very good impact resistance if you're able to build composites from silk with another material. So then you might start thinking of impact resistance. But also, there's a lot of medical applications as well because the body has a very low immuno-response to silk. Silk is being used as sutures before now. And so, you can actually start looking at making ligaments and tendons, vascular applications for silk. We're also interested in whether we could actually extend the range of properties to be even more useful for certain applications for us as well.