Flying spiders and silk antibiotics

Chris Smith spoke with University of Nottingham's Sara Goodacre, who studies money spiders and silk evolution to find out more about these high-flying arachnids...

Chris -
Well still with us, of course, is Sarah Goodacre who actually works on money spiders, do you know why they're called that, Sarah?

Sarah -
It's a really good question. So their formal name is the family Linyphiidae. They're also getting quite small, although some of them might be slightly larger and money spiders is the kind of affectionate name that we have for them.

Chris - What do they eat and how do they eat?

Sarah - Money Spiders are really great at eating pests in farmer's fields. They will eat pests in your garden, but the bottom line is they eat a wide range of other invertebrates and occasionally they'll eat each other, too.

Chris - One thing I've noticed about money spiders and not the bigger ones like Sally and Brian found. I didn't even know they could get that big in fact, but usually it's when they go drifting past me on the breeze. Cause you just see this web go by and there's a spider on the end of it. Is, is that an accident? Is that a spider accidentally got detached and it's now on a lifeline as it were, or is this intentional?

Sarah - Well, I think this is one of the behaviors that is so fascinating about spiders. Baby spiderlings of a wide range of other species, they deliberately take to the air. They use their silk as a sail, the climb to high point. It's been a meter or so of silk, which is quite lot, if you're already one or two millimeters long, think about it, and then the wind catches it. And the key thing is once they've made the decision to go up, they've got no control over how far they fly. And we think that some money spiders, so the one that you might've seen drifting past you on a summer's day and they've come from 70 kilometers away.

Chris - Wait, how long? 70?

Sarah - And of course, once they fly 70 kilometers, then once they start fying, they might do so again, the next day and the next day. And we know that some of them could even probably cross oceans. Because when they land on water, they can take off from there as well. And continue that journey.

Chris - How much silk is actually in a spider though, presumably a large amount of the spiders interior is the chemistry that makes silk.

Sarah - Spider silk glands are the most amazing little storage organs where they stole the liquid silk. They absolutely don't want to become solid inside the spider, but once it leaves the spider, we want a fiber to be formed or a glue, because some silks come across as glues. in fact, some spiders spit their silk at each other and spit the sticky glue at each other. Some of the silk that we see is incredibly fine. It's a thousand times finer than a human hair. So actually volume-wise, they've not used as much as you might think to make a really long thread, that's a couple of meters long.

Chris - I did read that people were interested in the medical applications of the silk because obviously it is very biocompatible and therefore it's likely to be well tolerated.

Sarah - So yes, the spider silk is tolerated very well by human cells. Unlike silkworm silk, for example, it really isn't. And because of this, we can actually use those properties to make our own artificial versions. And in my lab, in collaboration with chemists, we've actually added extra molecular twists to the artificial spider silk that we make. In that we've stuck antibiotics onto the silk as well, so that we can make it, as we say, even smarter than the spiders' itself.

Chris - How does that work then? And why, why would you want to stick antibiotics onto the silk?

Sarah - Well, what we think is that the silk might be useful in medical applications. And of course, one of the great challenges of the 21st century is, is microbes bacteria that really can infect wounds and cause all sorts of problems. And the clever thing here is that if we can take some of the properties that we wanted, a spider silk mesh or film, whatever it is we want to produce, and we can add the properties such as anti-microbial antibacterial activity, by sticking an antibiotic on, we can also make it such that the antibiotic only comes off and does its job when there are bacteria active. So we're making materials that are really smart. If you like that really work for what we need in a medical application and yet are inspired by and really built upon the natural world around us. And the inspiration that it's given.

Chris - What sorts of application would one of these antibiotic-laden silks have? Where would you deploy it?

Sarah - So we think that we would use antibiotic silk in something like tissue regrowth or tissue regeneration. One of the key things is you don't just have to stick antibiotics onto it, you can stick growth factors that act as little signals and direction lines for cells to grow along. And so really it's up to the user. What is it you would like your silk to have as an extra function? We know it can be sticky or stretchy. We know it's biodegradable, we know it's see-through, we know it's strong, we know it's fine, etcetera. What else do you want it to have? And if you want it to be antibacterial, if you want it to tell cells how to grow, all of these really are medical applications that we think will just give medics a different set of options for treating whatever condition it is that they're working on. If you think about how diverse the spider family is as a whole, probably there's a whole heap, more inspiration in there, just waiting.