Bioengineering

31 May 2009
Presented by Chris Smith, Kat Arney.

How does nature inspire technology and engineering?& We find out how bamboo may make effective wind turbines, and how the material that makes up locust tendons could soon be in your shoes and electronics!

In this episode

19:33 - Steam explosions - the science of popcorn

Steam explosions - the science of popcorn

21:33 - Bombardier spray cans

Aerosols and spray cans from the bottom of the bombardier beetle; Andy McIntosh tells us more.

Bombardier spray cans
with Andy McIntosh, University of Leeds

Chris - And it's not just popcorn that goes pop! Bombardier beetles are so-called because they quite literally bombard their predators with explosions from their rear-ends. They can actually expel boiling liquid over distances of a few feet. Now researchers have worked out how they do it and by copying their strategy they hope to build better aerosols and more efficient engines...one of the scientists doing that work is Andy McIntosh. 

Andy - These insects, bombardier beetles, are found mainly in the hot parts of the world. Although I believe they have been discovered on the south coast of England. They can be as large as two centimetres but usually they're a bit smaller than that. They have in their backsides the most amazing combustion chamber, Chris, which is about one millimetre long or smaller. They mix two chemicals: hydroquinone and hydrogen peroxide. Even before they come into the chamber (and nobody quite knows why) they don't react in the very small tube that comes in. In the chamber there is a mixture now of catalysts: peroxidase and catalase. These cause the  reaction to go much faster than it normally would which then heats up the water which is also there. It tries to expand but it can't initially expand and it can't vaporise therefore and boil properly until an exhaust valve, which is just a bit of cuticle - which won't really give way until there is a pressure rise sufficient to make it give way - when that goes then it basically suffers a vapour explosion. This all happens in 1/400th or even 1/500th of a second.

Bombardier BeetleChris - This is like you unscrewing the cap of a radiator of a car engine that's hot and the water still boiling as the pressure goes off. This is happening in the back end of this insect?

Andy - All the time when it's doing this, yes. It will do it for a few seconds. You're getting a huge number of blasts. If it goes on for ten seconds then obviously if it's doing it 400 times a second you can work out how many blasts it's doing.

Chris - Why would it do this?

Andy - Basically this beetle is being preyed on. Creatures like birds, spiders, ants are trying to get at this creature and they usually don't win. Very rarely a spider might be able to wrap it round in its web and eventually eat it but that's rare. They're usually stunned by this horrible mixture which is hot. Although they won't be killed by it they're be so stunned they won't be able to do anything for a few minutes and the beetle runs away.

Chris - It's an intriguing adaptation. It's amazing to think the beetle doesn't burn itself in the process. There must be some kind of adaptation that protects it. When you zoom in on the apparatus this beetle uses to do this what does that tell you about how it works?  

Andy - As I mentioned earlier there is an exhaust valve that doesn't give way until there's a particular pressure. Also you should note that there is an inlet valve which is, as the explosion takes place there is an expansion which causes the whole chamber to begin to pinch the inlet valve. As it explodes that stops more stuff coming in. What we didn't realise was that there was an exhaust valve which was made out of a bit of a cuticle which would only stretch under a particular pressure. We reckon it's about 1.2 or 1.3 bars. We're not really quite sure. Nobody's been able to get an instrument small enough to measure it.

Chris - The one thing that strikes me, when you hear a story like this is there are so many applications for what amounts to a spray gun. Could you copy this?

Andy - Yes. Just be aware that people are already using this pulse combustion idea for engines. There is such a thing as a pulse combustor engine. And indeed it was used in the V1: the German's didn't realise that was the same was what was happening with the beetle. Without realising it people have been using this type of idea already. What is unique about this is that it gives a facility for, if we can copy it, for actually getting a spray of liquid and controlling the droplet sizes if we know how to get the valve system working properly. Rather than relying on a passive system which is what the beetle does we have introduced an active system whereby we control when the inlet of water comes in and the outlet of steam and water takes place. We're able to actually use the idea of the beetle, not on the chemistry but on the physics of this valve system, to actually get some very unique spray gun (as you call it) applications.

Chris - Engine have to atomise fuel to get the fuel into the cylinder quickly and in a very widely distributed and with a very uniform particle size. That means the burn would be better straight away.

Andy - Absolutely. That's one of our major interested areas that we're developing. We know that we can, without using a huge amount of pressure to atomise the fuel which is what usually happens. We know that we can do this with much lower pressures, albeit we're using a vapour explosion idea from the beetle. We are using some pressure but nowhere near the pressures that people use at the moment. Also there's aerosols and other applications that these can be used for, maybe other pharmaceuticals as well.

Chris - I was going to say therapeutically because there are instances where you want to get very uniform, very fine droplet nebulised mixtures, for example. These will then be carried on the air deep into someone's lungs. Could you do something like that with this?

Andy - Yes. We think we can although we think that's a little bit of a long way off at the moment. We're pretty sure that just by using water, not fuel obviously (as in the fuel injector idea) but just using water we think we can use that as a spray which can produce steam and water which actually cools down pretty quickly and can take a drug which is in solution into a targeted area in the patient. We're not quite sure yet whether this will work out but we're certainly looking into that.

Chris - Leeds University's Andy McIntosh, who's working with the organisation Swedish Biomimetics 3000 to copy the bombardier beetle's spray technique.  

28:31 - Extra-elastic resilin

Chris Elvin tells us about the super-springy protein that his lab managed to synthesise.

Extra-elastic resilin
with Chris Elvin, CSIRO Australia

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.

FleaChris 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.

35:27 - Super-renewable bamboo turbines

Forget wind turbines made from vast sheets of metal - make them from fast-growing bamboo! Jim Platts tells us more.

Super-renewable bamboo turbines
with Jim Platts, University of Cambridge Institute for Manufacturing

Meera talked to Jim Platts of the Univeristy of Cambridge about bamboo in wind turbine blades

Jim - Because wind turbines are a rotating machine but they are in the turbulent boundary layer of the atmosphere they suffer very much from fluctuating loads, the materials which are best for dealing with that are fibre reinforced materials, metals aren't so good. So we can easily think of glass fibre, carbon fibre, or fibre-reinforced composite materials but actually wood is a naturally occurring fibre-reinforced material.

Meera - What makes bamboo more appropriate than other types of wood?

Jim - Many common species of wood have fibres running in lots of different directions, so a block of wood is strong in all directions, but some materials, bamboo is one of them, but you can also think of fir trees, the fibres in the wood are running up the trunk of the tree or up the stem of the bamboo.

Meera - Running in one direction?

Jim - Yes, if they are all running in one direction so you get better properties in that direction

Meera - So why is it more beneficial for a blade to have unidirectional fibres?

Jim - Well a blade is itself rather like a tree. It is fastened at the root end of the blade, and then it is a long cantilevered beam picking up what are heavy aerodynamic loads from the wind, so it is bending the tip of the blade, just like when a tree bends when the wind blows. So you want the fibres running along the blade to give it the tension and compression strength where the beam is bending.

Meera - What actually happens to incorporate wood from bamboo into a wind turbine?

Jim - When we are talking about bamboo we mean Mosa bamboo, which typically grows 12-15m high, the stem is 120mm in diameter and the wall is about 15mm thick, so this is big stuff. What we want is the skin of the bamboo, the outer 1-2mm at the outside of the bamboo which is where the fibres are most densely packed. So that is where we get our highest strength. The rest of the bamboo can be used for furniture or whatever, but this is the really hight tech bit. We then take those strips and stick them one on top of the other to make a plank and then to make the aerodynamic shape and strength of the blade we lie all these planks side by side and end to end to give us the structural strength. Then we cover it with a polythene bag, pump the air out and let resin flow in to stick them all together, which makes one completed structure with a fibreglass skin on the outside to give it a hard surface but all these bamboo strips stuck together inside to give it the technical strength to do the job.

Meera - You actually have some samples of the planks here, put side-by-side covered with resin, and it is very solid, you can't even feel any gaps between the planks

Jim - The resin is doing two jobs, sticking the planks together, but also wood has its best properties when dry so we have dried out the bamboo before we use it, and when the epoxy resin soaks around it the epoxy resin is a complete vapour barrier. A bit like all the chips in the silicon chips in your computer which are encased in epoxy to keep the moisture off them.

Meera - And of course bamboo has a negative carbon footprint

Jim - Yes if we compare bamboo to glass fibre or carbon fibre, we use a lot of energy melting the sand to make the glass to make the fibres, and this energy produces CO2. Because bamboo is a natural product it is actually a carbon sequestration itself. It is taking CO2 from the atmosphere and it is making a high quality structural material out of it. And over the 20 years operating life of the wind turbine it will give you as electricity 400 times the energy content of the bamboo to make the blades. So it has a negative carbon footprint and a huge energy payback.

Meera - So to get a few facts and figures about this then, a typical turbine made of bamboo, what would it look like, how big would it be and how much energy would it produce

JIm - A typical wind turbine is a tower 80-90m high the rotor on the top 80m in diameter, and wind turbine blades 40m long. 3 of those blades on a hub which will produce 1.5MW of electricity. And you would normally have those in a wind farm of 10s or even hundreds of wind turbines making a significant sized power station.

Meera - Where in the world is bamboo going to be used, as it isn't native to the UK?

Jim - There are several major countries with big bamboo resources. The industry is beginning to develop the technology in China.

42:07 - How do sunflowers follow the sun?

We ask how the mega-fast growing blooms of sunflowers track the sun and whether they can do the same with the moon.

How do sunflowers follow the sun?

We asked David Henke, Senior Lecturer in Plant Sciences, at Cambridge University...

It is actually very simple: there is a kind of driver which is growth. If you look at a sunflower there is a narrow neck which is growing, and it is in this narrow neck where most of the cell expansion, and therefore most of the expansion of the stem takes place. And this takes place at different rates on different sides of the stem. So, in the morning, most of this growth is on the West side of the stem so the flower tilts to the East; later on in the day you get stronger and faster growth on the north side, so the flower becomes tilted and so on until the evening when it ends up facing West. At night the growth is corrected and you have a great deal of growth on the West side so at the beginning of the day it is facing East again. This pattern is probably driven by some kind of internal clock, which is set by the transition at the end of the day from light to dark, which then starts the whole process of West side growth in the flower.

We know that the sensitivity of plants to light in terms of the sensors capable of picking up light are quite remarkable, and you can show that the light of a full moon on a completely clear night is just about perceptible to a plant, and the problem is that most of the time the moon isn't full.

Sunflowers do unwind at night using the same alternating growth mechanism as in the day. But what is also interesting is that no one really knows why the flowers themselves follow the Sun. The best guess is that they need more heat to grow more seeds...

53:01 - Do viruses have a metabolism?

Do viruses have a metabolism?

We put this question to Chris SmithChris - This is interesting in terms of biomimetics because people are talking about using viruses and their ability to infect cells and inject their DNA and RNA into cells for gene therapy so it's an important question. And the answer is no. Viruses are not alive they don't have a metabolism, they're nothing more than an infectious bag of genes which is able to put those genes into a cell and make the cell produce all the viral products to make more viruses. That's all they do.

53:36 - Does your DNA change through life?

Does your DNA change through life?

We put this question to Kat Arney.Kat - I could talk about this one for hours but basically yes it does. You pick up mistakes in your DNA as you go through your life due to damage from things like tobacco smoke, from the sun, and just from your own metabolism. That's eventually what causes things like cancer. And also, you get what are called epigenetic changes. These are changes to kind of the code around your DNA. So yes, your DNA is very different when you're older from when you're younger.

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