Harnessing the superpowers of silk

[THEME MUSIC] FLORA LICHTMAN: Hey, it’s Flora Lichtman, and you’re listening to Science Friday. You may have seen that the next Spider-Man comes out this summer. The trailer, which came out just this month, hit a billion views.

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– Because I’m not just Peter Parker, I’m Spider-Man.

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FLORA LICHTMAN: And relatedly, in a superhero story, this would be called a twist of fate. This question came in on our listener line.

CHRISTIAN: My name is Christian. I’m in Richmond, but I mean, I’m hailing from Pennsylvania. You know the vibes. I’m calling because I wanted to inquire about my ability to have a pair of functioning web shooters so I can operate as a local Spider-Man. And I would love for you guys to let me know.

FLORA LICHTMAN: OK, Christian, Sci-Fri to the rescue. Although, web shooters, for now, are the stuff of sci-fi, the spider-verse did get this right. Silk seems to have superpowers. So what can spider silk really do? And how are people trying to harness it?

On the line is spider silk biologist Dr. Cheryl Hayashi, senior vice president and provost of science at the American Museum of Natural History. Cheryl, thanks for joining me.

CHERYL HAYASHI: Thank you!

FLORA LICHTMAN: Off the bat, give me your first reaction to Christian’s question.

CHERYL HAYASHI: I love that question. We should always be inspired by nature. And who doesn’t want to have web shooters on their body?

FLORA LICHTMAN: I agree. Is this a personal fantasy for you?

CHERYL HAYASHI: It’s not to swing from buildings, but a personal fantasy for me would be if I could be a spider for a day and actually have the coordination and the ability to weave a web, that would just be amazing.

FLORA LICHTMAN: To weave a web, that would be your fantasy. Why?

CHERYL HAYASHI: Oh, my gosh, yes.

FLORA LICHTMAN: Why weaving a web?

CHERYL HAYASHI: Because it’s one of the most remarkable, wondrous structures that’s in nature. In order to make a web, a spider has to be able to make the silk, and they make that silk in their body. So in their abdomen, they have little tiny glands that pump out silk protein.

And then they have little spinnerets on their abdomens. And they touch their legs to the spinnerets, and that’s how they pull silk out. And then they have to have the right choreography in order to construct a web. And that’s just really hard to do. It’s just an amazing, amazing feat of engineering and design.

FLORA LICHTMAN: Yeah. OK. I mean, I want to be able to picture this. In Marvel movies, the silk is shooting out of, I guess, spinneret glands in Peter Parker’s or Spider-Man’s wrists. What does it actually look like on a spider?

CHERYL HAYASHI: So a spider has many, many silk glands, and most spiders have many types of silk gland. And each has its own recipe, its own recipe of silk ingredients. And so what comes out of these silk glands is a variety of different types of silk. Some types of silk are really strong. Some types of silk are stretchy. Some are sticky.

FLORA LICHTMAN: Can they tune the recipe for the area of the web that they’re making?

CHERYL HAYASHI: They do that in terms of– they draw out a particular silk for the particular architectural element of the web. So for instance, the frame and the radii, the spokes, that’s one kind of silk. And a different kind of silk, a much stretchier silk, would be used as the spiral that gets laid on the spokes. And so spiders are mixing and matching the different kinds of silks they make, depending on what they need to do with their silk.

FLORA LICHTMAN: So it’s not really spider silk, it’s spider silks.

CHERYL HAYASHI: Exactly. There’s not just one kind of spider silk. Each spider makes at least one silk. And each type of spider silk is made up of its own set of proteins. So that’s why I always say silks. So a lot of S’s in there.

And there’s over 53,000 described species of spiders. And so if you do the math– and most of them make more than one silk– there’s a lot of silk out there, a lot of spider silks to be studied.

FLORA LICHTMAN: Wow. Like, in the tens of thousands at least?

CHERYL HAYASHI: Oh, my gosh, yes, yes. Like, yes.

FLORA LICHTMAN: What were you going to say?

CHERYL HAYASHI: I would add a few more zeros to that.

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FLORA LICHTMAN: We hear these big claims with spider silk. Like, it’s stronger than steel. It’s tougher than Kevlar. Is that true for some silks?

CHERYL HAYASHI: Oh, yes, it is true for some silks. And people might say, how could that be true? You have to think about the scale. So spider silk is often so thin, you can barely see it. So it’s very fine fibers, but they’re able to do things like stop a flying insect. That takes a lot of strength and toughness.

FLORA LICHTMAN: Yeah. OK. Spider-Man obviously shoots silk out and then uses it as a mode of transportation. Do spiders use silk that way?

CHERYL HAYASHI: So spiders, they don’t necessarily shoot silk out like the way Spider-Man does. Spiders tend to more pull silk out, or they might attach silk to a substrate. Maybe it’s the eve of your window or a branch, and then they might use gravity to drop from it. So that’s a common way that spider silk gets drawn out. And then they can walk on that line.

Some spiders, especially tiny little spiderlings, let some silk out, and it functions sort of like a little parachute or a little sail, so they can be caught by the wind. And we call that ballooning. So spiders can basically fly around the Earth. In fact, you can even find spiders at high altitude, little tiny spiders at high altitude, flying with their draglines. So spiders never evolved wings, but they can fly with their silk.

FLORA LICHTMAN: That’s wild. Are there any other lesser-know uses of silk that we should call out?

CHERYL HAYASHI: Sure. So some other lesser-known uses of silk is there’s another spider called Ebola spider, which has changed their orb web down to a single line with a single ball of sticky glue at the end. So it’s like a little ball of snot with a little string attached to it. And when insects approach that spider, that spider starts swinging that bolas. And then that little sticky ball gets stuck to the insect, and the insect goes into tethered flight, and the spider can reel it in. I think that’s a super cool use for literally being a web slinger.

FLORA LICHTMAN: A spider lasso. I love it.

CHERYL HAYASHI: Yes, yes.

FLORA LICHTMAN: OK. I mean, here’s the thing, I don’t think I’m speaking out of turn here. I don’t think I’m going to say anything that’s surprising. Spiders, look, are not particularly well-loved, I would say, generally. And yet they do confer this great power in one of our most beloved superheroes. How do you think about our relationship with spiders?

CHERYL HAYASHI: Oh, that’s a good question. Of course, I don’t really relate to this thing about spiders not being beloved. I find them absolutely fascinating. And so, yeah, I think it’s fair, though, that they inspire. I mean, they’re so amazing. They’ve been spinning silk for hundreds of millions of years. They’re nearly everywhere in all terrestrial habitats. There’s even some spiders that live underwater. So I think they’ve earned their place in terms of inspiring us.

FLORA LICHTMAN: Underwater spiders?

CHERYL HAYASHI: Yeah, there are a few spiders that live underwater. Spiders never evolved gills, so they do need to have air. So you might want to guess what they trap their air with.

FLORA LICHTMAN: I’m going to guess the most amazing material known to man, spider silk.

CHERYL HAYASHI: Yeah. They basically go to the surface, and air sticks to their little hairs and their waxy body, and then they can capture the air bubble, and then they can put it into their little silk chamber. And they can–

FLORA LICHTMAN: It’s like a scuba tank, a spider silk scuba tank.

CHERYL HAYASHI: Yeah. And they can hang out in there. They can go back up to the surface and replenish. But there are some spiders that live underwater. There are spiders that live on the shoreline. And at high tide, they’d be submerged. And at low tide, they’re out.

So what they do is they live in little burrows, and they have a little door on it and make a little waterproof door. And you might want to guess, what is that waterproof door made of.

FLORA LICHTMAN: Silk?

CHERYL HAYASHI: Yes. It’s just amazing. It’s like better than duct tape.

FLORA LICHTMAN: Better than duct tape. Oh, I love that. I mean, are people trying to harness the power of spider silk? Is that a thing?

CHERYL HAYASHI: Oh, that’s definitely a thing. So it’s been long recognized that spider silk has these remarkable properties. And so there’s been a considerable effort into trying to understand what’s the secret? So people study the silk proteins. They study the silk structure.

And there are people that study, well, how can we replicate this? Do we replicate it by– do we mimic the structure, using other chemical means? Or do we actually try to make a lot of silk protein? And there’s research going on all in all those areas.

FLORA LICHTMAN: What’s the hardest part? Is it the fabrication?

CHERYL HAYASHI: The fabrication does seem to be quite difficult. And it’s just an amazing thing that when you either watch a spider make a web, or you just see silk lying around your house or outdoors, that there’s a little creature that’s doing something that seems so effortless for them that is really hard for humans to do.

FLORA LICHTMAN: Dr. Cheryl Hayashi, senior vice President and provost for science at the American Museum of Natural History in New York City. Cheryl, thanks for joining me today.

CHERYL HAYASHI: Thanks.

FLORA LICHTMAN: We got to take a break. But along those lines, when we come back, we’re talking to a biomedical engineer who’s trying to do just that, to fabricate silk and use it for devices like sensors and implants. Don’t go away.

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Up next, let’s talk about fabrication and how exactly scientists are putting insect silk to use. Here to pull that thread with us is Dr. Fiorenzo Omenetto, a biomedical engineer and director of the Silk Lab at Tufts University in Massachusetts. Fio, welcome back to Science Friday.

FIORENZO OMENETTO: Yeah, thank you.

FLORA LICHTMAN: You run a lab devoted to finding silk applications. Why silk?

FIORENZO OMENETTO: Oh, gosh, what a tough question to answer. Because from a material standpoint, it’s a very nice technical material. So it can be formed on the nanoscale. It can interface with electronics. It can make very solid blocks. And, and so have all these material formats that are very versatile.

But the thing that silk really does is it’s able to store and preserve the activity of what you mix inside of it in these end formats. And an example is, for instance, if you take a glass of silk, and you add some blood inside of it, and then you pour it on the table, and you let it dry, once you lift up a sheet of material that looks like plastic, like a red transparent film of plastic– and you can leave it on the table for several months, and then cut a little piece and send it to the hospital, and then they’ll take the blood out. And your analysis, your labs from that blood are just as good as a fresh blood draw.

FLORA LICHTMAN: What? It’s like a– that’s an amazing preservation device.

FIORENZO OMENETTO: It’s the one thing that makes working with this material very exciting because you can hide superpowers in materials. So it’s really a material scientist dream. It gives a lot of opportunity to explore in domains that are otherwise very hard to explore.

FLORA LICHTMAN: And you use worm silk, right? Not spider silk.

FIORENZO OMENETTO: We use silkworm silk, yes. We use silk that commonly is used as a commodity material for textiles, so there’s an abundance of it. And we deconstruct it into its liquid state so that we can then reform it into a variety of materials.

FLORA LICHTMAN: Well, what is it about silk? What’s the secret sauce that allows it is to do this, that allows you to store super powers in a material?

FIORENZO OMENETTO: I wish I could tell you that this was designed with purpose and equations and then long hours, but I think that this is something that comes from directed evolution of, in this case, from domesticating the silkworm over thousands of years. And ultimately, the selection was to make the strongest, finest, the most lustrous fiber that would give you the suppleness scarves and the best garments that you could weave.

But ultimately, this gave a molecule, a particular kind of molecule that is very, very unusual in the way that it assembles and in the way that it interfaces with the materials that it’s mixed with. So I think it’s really nature’s offering, in a way, a very technologically sophisticated polymer that happens to be very benign and very friendly to interface with the body or to disperse in the environment.

FLORA LICHTMAN: I mean, I feel like I often see silk for sensors, like, biosensors or within the body or outside. Is that, again, just because the silk can hold the actual sensing material and keep it stable in lots of different environments? Or is it playing any other role?

FIORENZO OMENETTO: Well, there’s a little bit of both. I think that the main advantage or the main feature is really that silk will stabilize chemistries that otherwise are confined to laboratories and to wet labs and to a lab bench. And so you can imagine really, that you can make silk inks that contain enzymes that otherwise would need to be refrigerated, and you can just print them on surfaces, and then just look at the way that the surfaces react to the environment around them.

And so this is a very nice way of using the stabilization function in the bioavailability to do all sorts of sensing from little adhesive patches and Band-Aid-type reporters to printed T-shirts that react to your body, to tapestries that you hang in a room and respond to the environment around it.

FLORA LICHTMAN: I do not want my T-shirts responding to my body more than they already do. Just saying. OK. Are there silk uses in the wild that I might encounter at a store?

FIORENZO OMENETTO: So the process of generating silk solution has been scaled up and has been put to industrial use in food preservation, in vaccine stabilization. To give a couple of examples, and now the production has been scaled to very large amounts. So yes, you may encounter it in these domains.

FLORA LICHTMAN: Yeah, I love that this very ancient biomaterial is being used in these kind of futuristic sounding ways. How do you think about that?

FIORENZO OMENETTO: I think that it’s beautiful. I think that there’s a recontextualization of things of things that used to be artisan skills and have been around for such a long time. But there’s a beauty in reimagining things and finding new contexts for materials that have been around for a long time.

Sometimes, I talk about– I give this example of maybe there’s an artisan in the world that is just the best person at doing shoelaces and braiding the best shoelaces on the planet. And this craft has been pushed out by industrialization and volume and scale. But that craft becomes contemporary if the material that you use to make the shoelaces now becomes a material that is medically relevant and can be used to replace ligament and tendons. And so all of these things that we have around and that have all these unbelievable properties, either from nature or from people using natural materials have, I think, a beautiful second life, and maybe a third and a fourth life.

FLORA LICHTMAN: It’s a lovely place to end. Dr. Fiorenzo Omenetto is a biomedical engineer and director of the Silk Lab at Tufts University in Massachusetts. Thanks for joining me.

FIORENZO OMENETTO: Thanks for having me.

FLORA LICHTMAN: I want to thank you, Christian, for dropping us a line. And listeners, if you have a spidey sense about a certain question you think we could help with, you’ve surfed the web but haven’t found an answer that sticks, give us a ring. We love hearing what you’re interested in, and we love looking into your questions. 877-4-SCIFRI. 877-4-SCIFRI. Just leave us a voicemail. This episode was produced by Rasha Aridi. I’m Flora Lichtman. We’ll catch you next time.

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