Extra-elastic resilin

Chris Smith - We're exploring how biology can influence technology and a very springy example is the stuff that keeps the wings of a bumble bee flapping. Joining us from the CSIRO's headquarters, I suppose you could say, in Queensland, Australia: he's here in Cambridge for a meeting. That's Dr Chris Elvin. Hi Chris.

Chris Elvin - Hi, Chris.

Chris Smith - So tell us a bit about this bumble bee's chemical that keeps it wings springy.

Chris Elvin - So this is resilin. This is a protein that's a polymer of amino acids and it's found in probably all insects where it enhances the efficiency of insect flight. It was discovered by a Danish researcher here who became Professor of Zoology here in Cambridge back in the sixties. He did some very elegant experiments to show that this was an almost perfectly elastic material. In other words it loses almost no energy as heat when it's stretched.

Chris Smith - So you stretch it and let it go and it returns almost all of the energy that you put in.

Chris Elvin - Exactly. Nearly all of the energy that's put into it is returned: about 97%.

Chris Smith - Chemically, how's that achieved?

Chris Elvin - It's achieved by having an almost completely unstructured random structure for the protein, if you get what I mean. It's cross-linked. There are covalent cross-links between chains of the proteins that allow it to act as a random network polymer which is exactly what you need if you were designing a perfectly elastic polymer.

Chris Smith - How does nature use it?

Chris Elvin - Well, it's as I said. It's present probably in almost all insects that have been looked at. We've certainly looked at it at the gene level in fleas, in dragon flies, butterflies and drosophila. We've pulled those genes out.

Chris Smith - I think mechanically what I'm getting at is we've got wings. How is it attached to the wings? Is it actually intrinsic to the wing material?

Chris Elvin - Well, it's both. It's found in the joins of the wing veins in dragon flies, for example, but it's also found as a major component in a tendon which is attached to the muscles which are attached to the wings. It's that large tendon which Weis-Fogh worked on back in the sixties and poked a tiny little wire, silver wire down through the hole and hung weights off this thing. He showed that when he released the weights it sprang back to exactly the position it was at the start. So it's there on the down stroke when the insect uses its muscles to pull down. This tendon is stretched and then the energy that's stored is released when it comes back up.

Chris Smith - Why is it called resilin? Is that because it's very resilient?

Chris Elvin - It's from the Latin, resilier: to bounce back. He named it resilin.

Chris Smith - Ingenious. Obviously something with those kind of properties would be extremely useful if we could work out how to make this stuff.

Chris Elvin - Absolutely. So we've taken a part of the gene from drosophila and we've published this in Nature back in 2005. We're able to express just part of the gene in E. coli so we turned the E. coli bacteria into little factories. They made the protein. It was a liquid protein solution and we cross-linked it using a photochemical method. We add a catalyst with a photochemical catalyst and an oxidant, we flash it with white light and it turns from a liquid into a rubber. This has the properties of the native material.

Chris Smith - What you're saying is you can steal the gene from the fly, get bacteria to make a sort of precursor form which you're then able to activate. How much can you make?

Chris Elvin - We could theoretically make kilos of it if we wanted to. We've made 100g or more in a large fermenter in CSIRO in Australia. We can then purify that protein using some neat protein chemistry techniques and get it almost pure and then cross-link it with light.

Chris Smith - Say you wanted to make a structure with this. We sold this on this week's show as bad backs. I think the stat you told me a few years ago was a person bends their back 100 million times in their lifetime. A bumble bee flaps its wings 500 million times in a lifetime therefore we think this protein could be used to repair bad backs. Tell us how.

Chris Elvin - We think that's the interesting bit. What you want for a spinal prosthetic disc, because that's what we're talking about, is a number of things. One, you need to have a material with a very high fatigue lifetime. You've mentioned 100,000,000 cycles for the number of times we move out back in our lifetime. This material form a materials point of view has that specification. It can last that long before the bonds break down. What you also want is for the materials not to degrade. This is a protein, it has peptide bonds in it. Proteases will break it up. We need to make it non-proteolitically-sensitive.

Chris Smith - Can you do that?

Chris Elvin - Yes. We have an ARC grant project with Monash University and the plan there is to use non-natural amino acids: beta or d-amino acids which aren't recognised.

Chris Smith - Very clever. So by using things you wouldn't find in the body or nature even they have the same chemical properties but they don't look right. Therefore they can't be broken down by enzymes. Ingenious, then you could cast a disc and put that into someone's back.  When would we see this? I've been doing a lot of digging, Chris. My back feels a bit sore. Is this going to be in my lifetime or is this way out there into the future?

Chris Elvin - I think we're probably talking ten years probably. There are some other things that need to be done to it too to make it - it's very soft material. Insects are very small so they don't need stiff springs. It needs to be stiffer and we can do that as well. We've got some ideas to do that.

Chris Smith - Puts a whole new meaning on that movie, The Fly.

Chris Elvin - It does. Thank you for coming to join us. That was Chris Elvin who's a researcher from the CSIRO in Australia. I wish you luck and have a wonderful trip back to Australia. Wonderful country, it's good to have you here in England. That was Chris Elvin from the CSIRO, explaining how you can make the gene product of resilin, this protein that keeps a bee's wings flapping.