Flexible Insect Protein Inspires Super Rubber

Resilin is a protein found in insects that allows them to jump long distances and beat their wings quickly. The material stores and releases energy due to its unique structure. Biomedical engineer Kristi Kiick is researching how to use these pliable proteins for medical purposes.

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IRA FLATOW, HOST:

Welcome back. I'm Ira Flatow. Have you ever wondered how a flea that is less than half an inch long can jump nearly 12 inches into the air? Or how a dragonfly can beat its wings 30 times a second? Now, before you swat them away next time, I want you to take a close look - and I mean a really close look - at their joints.

The secret to these tiny athletes is a protein called resilin, and it's found in the hinges of many insects. And that highly elastic protein allows for a quick release of energy and a quick getaway. It's like snapping a rubber band. Can we harness that energy and efficiency of that resilient resilin? My next guest is researching just that.

Kristi Kiick is a professor of material science and engineering and biomedical engineering at the University of Delaware in Newark, and she joins us from WHYY Wilmington. Welcome to SCIENCE FRIDAY.

KRISTI KIICK: Thanks, Ira. I'm glad to be here.

FLATOW: You're welcome. Where exactly do you find this natural resilin?

KIICK: In nature, it's found in, as you mentioned, the various joints of insects. In our lab, we find it from E. coli, which is the way we produce it in the lab.

FLATOW: So you're making a synthetic version of it?

KIICK: Yes.

FLATOW: Is that the right way? Or are you just reproducing the same stuff, but letting the E. coli make it?

KIICK: So there's a couple of different ways that you can look at making resilin in the lab. We've been using molecular biology recombinant DNA methodologies to take the amino acid repeats in resilin that are thought to give resilin in nature all those excellent properties that you mentioned, and to repeat them multiple times. And then we can engineer in extra biological activity or degradation activity that we'd like into the materials for the particular applications that we're looking at.

FLATOW: Now, is there anything as good in humans, as similar to resilin in humans?

KIICK: The energy store in mammals is a protein called elastin. And if one looks at the properties of native elastin and resilin in insects, the natural resilin, their properties in terms of mechanical properties can be pretty similar. Their properties chemically are a fair bit different. When researchers have tried to look at engineering versions of the elastins versus the resilins, that's where - at least at this time - it looks like the resilin-based materials, synthetic, have improved resilience over that of some of the synthetic elastins.

FLATOW: So that's a good way, a much better way of saying resilin beats out the elastin, no contest.

KIICK: At least in the data that we have to date for the resilin-like peptides, that's true.

FLATOW: So natural resilin is less rigid. It can stretch long distances. It's much, much better.

KIICK: It's very stretchy, and the thing that makes it interesting for the particular applications that we're looking at - and I think that has captured the interest of scientists across the world - is not only its resilience, which is its ability to release energy after energy has been put into the material, but it's also the fact that it does respond over those high frequencies that you mentioned in the intro. So for particular applications where it'd be very useful to have things with a high-frequency energy feedback that would be useful for certain biomedical applications.

FLATOW: In other words, something that can bend back and forth without breaking a lot of times, like, you know, if you have an insect flapping its wings, it's got to do that thousands and thousands of times before, you know, without snapping the hinges off.

KIICK: Yeah, that's right. Millions and millions of times.

FLATOW: Millions. And that's what's resilin can do, and where - I'm thinking of, like, where would that be useful in medicine? I guess your knee joints, something like that, or other places?

KIICK: So, yeah, so maybe people who had resilin in their knees could suddenly become much better athletes. We've been looking not necessarily at applications like that, but applications such as cardiovascular engineering. Heart valves could be a potential application. And in our particular lab, we've been looking at materials that can be used to help heal vocal folds.

FLATOW: Tell me a little bit more about that.

KIICK: Yeah, so this is a collaboration between my labs and another lab at the University of Delaware and a lab at the University of Wisconsin. We've been looking at these high-frequency properties of resilin, and are wondering if that might not be useful to help heal damaged vocal folds. Vocal folds - you know, when I was a kid growing up, we often called them vocal chords, and I think many people do that. So I had this image in my head of like a little harp that would be - provide the sound of different pitches when one spoke.

What is actually true is that the vocal folds are these two small - they're only millimeters in size - pieces of tissue that close together on one another and control the production of sound. So when those vocal folds get damaged, it causes a lot of problems in speech, which has a lot of implications for health, in human health.

FLATOW: Have you had any success in using resilin for treatments of the vocal folds?

KIICK: So, we're not quite that far in our research yet. So we've been interested in designing the biological activity of resilin, so to keep the structurally great properties that the natural protein has. And then to endow on that protein the properties that would allow it to bind to cells, that would allow cells to degrade it and remodel it. So we've gotten to the point where we've been making these materials, and we're looking now at injecting them in vivo in models to see how well they perform.

FLATOW: You know, scientists are creating new - or repairing new structures. They make an underlying structure, and then they try to grow stem cells on top to make organs and things. Could resilin be used in any of those kinds of applications?

KIICK: It's possible. So, some of the applications where elastomeric properties are useful - in particular, cardiovascular applications, or things around heart applications would be a particularly good target for resilin. We think that the resilin has perhaps a better fit with the high-frequency applications, but there's no reason that it couldn't also be used in these lower-frequency applications, as well.

FLATOW: There was some mention in the literature talking about modified resilin with gold nanoparticles. Wow. How does that work?

KIICK: So resilin has different properties in solution that allow it to bind to surfaces in different ways, depending on the conditions that the solution is under. So it can adopt different confirmations that can give it different properties. One of the things that's true of resilin - and it's observed in the cross-link structures - is that it's fluorescent. So when one can immobilize resilin on gold nanoparticles, it can allow control of light production, and to couple that with the gold nanoparticle, to act as a sensor for particular analytes in solution.

FLATOW: You say it gives off light? Does it do that when it bends? Could you look at an insect and see it when it's flapping its wings there, giving off some light?

KIICK: If you shine a light on an insect that excites the resilin in the right way, you could see the fluorescence. But to date, to my knowledge - that would be really cool if you could do that - but it doesn't light up when you bend it. I might have to think about how we could do that in the lab.

FLATOW: All right. We've given you an assignment for the weekend.

(LAUGHTER)

KIICK: Don't tell my husband.

FLATOW: Tell your husband. Well, no one's listening, so you don't have to worry about that. What about industrial purposes? You know, you have rubber, you have plastic. Somebody's going to say, well, you can make a tire out of it. It rolls, or something that's, you know, can be used in industrial purposes that vibrates a lot. Could you use resilin for that?

KIICK: Right. So the mechanical properties of the resilins that have been made to date probably aren't strong enough to make a tire. And if you were to make a tire out of it right now, it would be a very expensive tire. So in thinking about the commercial applications for resilin, I think probably the best area to look initially is in some of the biomedical applications.

But you could consider, if it were a small component of any of the larger type commercial products - say in a shoe or in a tire or in cosmetics - that it might have applications there, as well. But I think it's pretty early in the game to know if that's going to be true yet or not.

FLATOW: What about vibration damping, you know what I'm saying? You put rubber in things to keep it from damping the vibration. Now it's going to vibrate a lot and stay strong. Could you use it for something like that?

KIICK: Yeah. Absolutely. Absolutely.

FLATOW: You know, in computer parts, or a new cellphone part or something. You drop it on the floor, it's got resilin in it. And you could advertise: made with resilin on the...

KIICK: It bounces right back up into your hand.

(LAUGHTER)

FLATOW: Exactly. Let's talk a little bit about biomedical engineering. As a biomedical engineer, do you often look to nature for inspiration? I mean, it's all over there, isn't it?

KIICK: Yes, we do look to nature. We look to nature in a variety of different ways. In our particular labs, we're interested in understanding how materials that support cells and support their behavior can be engineered based on natural principles. So we look to resilin because of its mechanical properties. We also have research in various other types of peptide and polymer-based materials where we're interested in assembling and organizing the materials in ways that mimic how the proteins and polysaccharides that surround cells are already arranged. So there's a lot of inspiration there.

In various other areas of bioengineering, people have looked at viruses for inspiration for carrying drugs, carrying DNA into cells. If you look at the interference-based coloring of butterfly wings, there's big inspiration there for photonic materials. So there's a lot of different ways that bioengineers look to nature to try to design new structures or new biomedical materials.

So bioengineering itself is a really wide field, and where we play is mainly in the area of biomedical.

FLATOW: Do you ever get together with insect folks, maybe, or somebody like Gail Wilson, somebody like that, and just schmooze about what might be good, fertile ground to look into?

KIICK: You know, we haven't done that yet, so we've been really focusing on our interactions with cardiovascular biologists and vocal fold clinicians. But reaching out to the insect folks would be a great idea.

FLATOW: You know, there's a great - there's an old book, "Micro." You're familiar with Michael Crichton's last book, or he wrote part of it?

KIICK: I'm familiar with it, although I haven't read it.

FLATOW: Ah, but you should, because you'll get a lot of inspiration from that book. We're going to do that book as part of our book club coming up soon, I think, because it's such an interesting book.

KIICK: Yeah. Excellent.

FLATOW: Yeah. All about what's going on on the floor of the forest and all kinds of things, with the insects, and we'll get into that later. Thank you very much for taking time to be with us today.

KIICK: Thanks, Ira. It was a pleasure.

FLATOW: You're welcome. Kristi Kiick is a professor of material science and engineering and biomedical engineering at the University of Delaware in Newark.

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