In Our Time - Macromolecules

Episode Date: December 29, 2011

Melvyn Bragg and guests discuss the giant molecules that form the basis of all life. Macromolecules, also known as polymers, are long chains of atoms. They form the proteins that make up our bodies, as well as many of the materials of modern life. Man's ability to mimic the structure of macromolecules has led to the invention of plastics such as nylon, paints and adhesives. Most of our clothes are made of macromolecules, and our food is macromolecular. The medical sciences are making increasingly sophisticated use of macromolecules, from growing replacement skin and bone to their increasing use in drug delivery. One of the most famous macromolecules is DNA, an infinitely more complex polymer than man has ever managed to produce. We've only known about macromolecules for just over a century, so what is the story behind them and how might they change our lives in the future?With:Tony RyanPro-Vice Chancellor for the Faculty of Science at the University of SheffieldAthene DonaldProfessor of Experimental Physics at the University of Cambridge and a Fellow of Robinson CollegeCharlotte WilliamsReader in Polymer Chemistry and Catalysis at Imperial College, London Producer: Natalia Fernandez.

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For more details about In Our Time and for our terms of use, please go to BBC.co.com.uk forward slash radio four. I hope you enjoy the program. Hello, they're in our houses, in our clothes, on our desks at work, in the car, in our food, and in the fabric of our bodies. We couldn't live without them. And yet we didn't know they existed until less than a century ago. The indispensable life-giving entities I'm talking about are macromolecules,

otherwise known as giant molecules or polymers. We've learned to copy the structures of these naturally occurring phenomena to make all kinds of plastics, fabrics and materials. From washing powder to aeroplane construction, they're an increasingly vital part of the modern world. And today, scientists are finding revolutionary new uses for them, from drug delivery inside the body to ultra-thin computer screens. With me to discuss macromolecules,

are Tony Ryan, Pro Vice Chancellor for the Faculty of Science at the University of Sheffield, Atheney Donald, Professor of Experimental Physics at the University of Cambridge and a fellow of Robinson College, and Charlotte Williams,

reader in polymer chemistry and catalysis at Imperial College, London. Tony Ryan, can you just tell us what macromolecules are? So, macromolecules are giant molecules. So often they're made from joining lots of little molecules together. So polythene of the polythene bag

is a polymer. The word comes from the Greek, polymene, many, Miros little things. And the little things are ethylene molecules, two carbons and four hydrogens. And you join them together because there's a double bond between the two carbons.

And you can open the double bond and join one molecule to another and make a long chain. And there might be a million ethylene molecules joined together to make one polyethylene molecule. But we have salt, and that is two items, isn't it? salt. Yes, I'm just trying to get to the listeners the idea of the size of this macro, the macromolecules.

Salt is two items. Now, what would a, what would a macro molecule, the size of a macromole? Well, so a polyethylene macro molecule. So the ethylene part is six atoms, right, two carbons and four hydrogens. And the polymany might be a million. So there'd be six million atoms in a polyethylene molecule, all joined together in a big long string. so there'd be carbon, carbon, carbon, carbon, carbon, carbon, carbon, carbon, carbon, carbon, carbon. Then each of those carbons has two hydrogens attached to it. You're opening your arms about, when you've gone even further. Bigger than the biggest fish. Yes, really?

Yeah. And how, so they're around this room, we're in this studio now, four of us around this table, where are the macro molecules manifesting themselves? Everywhere. I mean, absolutely everywhere. Well, give us some instances. All the claws you wear, whether it's wool, a protein. cotton, a polysaccharide,

P. E.T. Polyester, a synthetic polymer. Nylon, a polyamide. All of those are polyamers. The screen that's in front of the microphone is a polymer. The foam that's on the microphone is a polymer. Is there anything more you want to say about the structure of the macromolecule? So often we talk about them as being coiled up and being entangled like spaghetti in a pan. And if you had a microscope, an electron microscope, and you could zoom in and see individual molecules, you might see those tangles.

But in some cases, like in your tie, which is perhaps made of silk, then the polymer's protein, and those silk molecules, those protein molecules, are aligned together to make sheets where all the molecules stack up next to each other, like a row of pencils in a box. and then there'll be parts of the molecules that are stacked up and they're joined together by coils. So how can I see the macro molecules in this time? Well, you can't see them because they are molecules. It's very difficult for us to image a single molecule. You might be able to do it with a device called an atomic force microscope. It's a stick, a very pointy stick.

And basically the point on the imaging, stick is one atom and you can tap on a surface that you've absorbed a single polymer on and then maybe get a look at a single polymer. But these macro things are supposed to much, much bigger but even so you can't see it. Yeah, but the big collections of atoms

and imaging individual atoms is very, very difficult. Ithena, can we talk a bit more about the natural macromolecules to start with? Tony's mentioned proteins. Can we develop the idea of proteins so that listeners get an idea of what protein macromonicles are like and what they're for. Okay, so in nature, as opposed to many of the things that Tony's been talking about, which is synthetic, in nature there are three main classes of macromolecules.

So there are the polysaccharides, which are often structural, so things like cellulose in trees and things like that. And starch is another example of a polysaccharide, which is an energy storage mechanism for plants. then there are nucleic acids, DNA, RNA, which are concerned with processing genetic information, if you like. And then there are the proteins, which are very much the functional macromolecules in nature. So for the proteins, Tony's been talking about polythene, which is lots of ethylene repeat units.

In proteins, the repeat units are coming from the amino acids. There are 20 naturally occurring amino acids, and you can string them together through a peptide bond to make a long chain molecule. And whereas in polyethylene, each repeat is identical. In proteins, you have this library, if you like, of 20 different motifs you can use. And they are put together in a specific sequence. And each protein will have a very specific sequence. And that specific sequence is absolutely crucial to the way it functions.

So if it's not, if something goes wrong in our bodies, in the way we synthesise these proteins, then we can end up with some of the horrible genetic diseases. So there are different sorts of macromolecules going into different sorts of proteins. Well, each protein is an example of a macromolecule, and each protein will be identical. The muscle proteins, for instance,

they will be specific to their function and the proteins that are involved with signaling molecules, for instance. They will each be specific. So there are hundreds, thousands of different kinds of proteins in our body, each doing a very specific thing, each with a particular sequence of amino acids. So each, whatever it is, will be equivalent to each other, but the different proteins will be very different. You mentioned muscles. Can you give us some idea of the range of functions, that the sheer range that proteins, the protein macromolecules, have to perform? Yes, in our bodies, they are

covering essentially everything associated with function, so that, the proteins, the protein macromolecules have to perform. They will deal with motion of cargoes with transporting material through a cell. They will be associated with motors so that they will, motors are a way of transforming chemical energy into mechanical energy. They're very important as enzymes and as signaling molecules. And in both those cases, we haven't talked about the shape of proteins, but many of them are globulus, basically spherical. They coil up in a very specific shape.

And when they coil up, they may have a sort of cleft in their outer region where you can grab a parsing molecule. And so you can hold it there in that very specific cleft, a sort of lock and key kind of mechanism, and then carry out some reaction or the fact that that molecule sticks in that cleft can change the overall shape of the protein itself, and therefore that is a way of transmitting information. so that's part of the signaling.

So that their shape is absolutely crucial and that shape comes from the amino acid sequence along the chain. Can you give us an example of how it works in skin, for instance? Well, in skin... People will be rubbing their brow as I am so they're very close to their skin at the moment. Well, skin, if you like, is a protective layer

and you will have many macromolecules coming together to make that layer of skin. So that is designed to be predominantly waterproof to keep ourselves together. It's got to have a lot of mechanical resistance. So the collagen in it, as we age, the collagen molecules can form new bonds between them. And that reduces the elasticity, which is why our skin changes in appearance as we age. Charlotte Williams' micromolecules, obviously, they've existed for millions of years and they're part of every living organism.

but they weren't actually discovered by scientists until relatively recently about a century ago. Can you tell us how this breakthrough happened? Yes. Well, the first events in macromolecular synthesis were the production of materials that were trying to model natural species. So, for example, Baker-Lite was trying to model shellac, and Parchaseen, a very early polymeric material, was trying to model ivory, synthetic equivalents for natural species. materials. But at that time, they didn't understand very well what the structure of the molecules was.

And it wasn't until the 1920s that this became quite well established. So the prevailing dogma in the scientific community was that macromolecules didn't exist. They were small molecules that were loosely associated with one another and there were weak forces between them. But Herman Staudinger in the 1920s argued that in fact both naturally occurring macromolecules like cellulose and the synthetic equivalents like natural rubber and the emerging new materials were in fact single molecules with very, very high weight, as Tony described, single molecules with the same repeat unit repeated many thousands of times. And through careful experimental study in the 1920s, and in collaboration with people using x-ray crystallography to study the structure,

they were unable to establish that they were indeed large molecules and not loosely associated clusters of smaller molecules. But it was a very controversial theory in the 1920s. Can you tell us a little bit more about Herman Stadinger? Yes. He was a fascinating scientist. He took this very big move from being an organic chemist in his early career working on small molecules.

Where was he working? Where? In Zurich, in ETH in Zurich, and then later on at Karsra in Germany. And he made the move into macromolecular science and began to study natural rubber and carry out experiments to try and establish his theory that it was a macro molecule. Why were people so resistant? Because they had an alternative theory. They believed that the molecules were these collections of small molecules

that were clustered together. And many of his colleagues in organic chemistry were critical of studying her and told him to simply purify his compounds, and you will find they will crystallise. they will be small molecules. But in fact, through the experiments he carried out with x-ray diffraction and with chemical reactivity and viscosity and solution molecular weight determination,

he was able to establish that they were indeed large molecules. Can you give us some idea how the structure of a macromolecule affects its behaviour? The structure of a macro molecule depends critically on the small molecule, the monomer that makes up the polymer. And so if we think a little bit about the example, that Athena used of peptides. Synthetically we can make molecules that have the same type of chemical linkage, and these are known as nylons or polyamides.

And even within that synthetic class, by varying the monomer, you can go from nylon, which is a good fabric and a good fibre, all the way to a material like Kevlar, which is an extraordinarily strong and tough fibre and very, very heat resistance. So you might use it for fireproof clothing or bulletproof jackets. and so on. So the chemical nature of the repeat unit is very, very important, but additionally, the forces between macromolecules are extremely important. And this idea that the chains of macromolecules can line up with one another to give regions that are crystalline or very

highly ordered is very important in determining the eventual mechanical properties of macro molecules. If we think of another example that Athenia and Tony referred to, which is cellulose and starch, these two molecules have the same monomer, which is glucose, the same repeat unit, but the forces between molecules differ. So cellulose have a very crystalline structure, and this gives it great strength, and so it's used as nature's natural reinforcing material. On the other hand, starch is largely composed

of amylase and this has a much less ordered structure and so can be much more easily broken down and digested and hence it's the energy storage material and the material that we eat. Tony Ryan, can you tell us how the micro molecules are created in the laboratory? My favourite example is the first one I ever saw. What do you mean by saw? You've told me how we couldn't see it?

No, no, the first polymerisation I ever saw. So the first time I saw, polymer's being made. I was 12 or 13. And the school teacher did an experiment in the chemistry class. And they had an oil with one of the monomers in and water with the other monomer in. And mixed the two monomers together. Well, mixed the two liquids together, so very carefully. So that there was a thin layer between them. And the polymer formed at the interface. So an acid, reacted with an amide at the interface to make the bond

and the fact that there was an interface, a very thin layer between the oil and the water, controlled the amounts of acid and amine that saw each other and he pulled this strand of polymer out of the middle.

It's called the nylon rope trick. It's fantastic and it looked like a trick and it made this material that's quite strong and I've used it many, many times in teaching. In fact, a colleague and I once went up 12 flights of stairs pulling this material away from the interface. We had to make a really, really big flask so that we knew there was enough material there.

And you can imagine the strength of this polymer. Did you use it like a fireman's ladder and shim me down it? Well, and that kind of got me interested in how spiders make their polymers. So in the lab, you know, we took two chemicals, we separated them in oil and water, mixed them together at the interface, and then we could pull this string, this rope of nylon from the middle.

Up 12 floors? Up 12 floors. And it supported its own weight. That was the amazing thing. That's how strong it was. If you left it alone, it stood still. Well, you could just, you literally, you know, the flask was at the bottom

and we were walking up the stairs holding these pair of tweezers and up and up and up and up and up and up and up, and up and up, it went. But everyone, so if you do a bit of DIY, and you use gap filler. You know the foam that comes in a can? That's essentially the same polymerization,

but it produces carbon dioxide, and so the material forms up when you squeeze the button on the can, you release the carbon dioxide, and that allows the molecules to join up together to build this massive cross-linked polymer in this case. It's not a single strand. These strands cross each other to make a network.

And then that network becomes solid, but it traps the gas and you can fill a gap. You've just given the best advertisement I've ever heard for teaching chemistry and laboratory at schools. I think they should put this into a little capsule and send it to Michael Gove to send around the educational system. Well, Athenia, can you tell us, are you looking for properties in natural macromolecules

that you can replicate synthetically? Certainly sometimes. And what are the main ones you looking for? Well, Tony's just mentioned spider silk. So let me develop that theme as an example. A spider can eat whatever it finds, and so it's got a random supply of material, and it doesn't work with horrible organic solvents.

It basically works in a water environment, but it is able to produce this silk, and indeed it produces many different kinds of silk for different parts of the web. But the silk is itself biodegradable, but incredibly strong. If you look at the strength, per weight, it's better than steel.

But the trouble is... Just a second. Per weight, proportionally, it's stronger than steel. That's right, yes. And people have studied spider salt, trying to understand what it is about it, how the different sequences come together to crystallise, is that relevant? But the crucial thing is that the spider is doing this

from a variable diet. If you have a big chemical factory, you tend to be very careful about what you put in to do your polymerisation. But the spider can do it using just what it happens to eat, and it does it in a water-based environment, which is environmentally very important. So if we could learn how and what it is

about the way the spider processes, it would be a really valuable thing to learn. Tony, you have to come in. I've done research in this area, and it turns out that to make a fibre from silk takes about a tenth of the energy input that it takes to make a fibre from polythene, and about a 50th of the energy it takes to make a fibre from nylon.

So using the special properties of the polymer and water and how the material flows through the back end of the spider, evolutions allowed us to make really, really low energy intensity engineering materials. And also this material is then biodegradable. We aren't completely smothered in spider silk. It does slowly get sort of broken down in nature. So if you covered it properly, the whole polythene plastic problem would disappear. Oh yeah.

But the big companies can't afford to do it. Well, and it's oil is very, very, very cheap. We don't pay the proper price for oil. So how does that come into the configuration? Well, because so the monomers are cheap and the energy to convert them from monomer into polymer and then the energy to convert them from polymer into artifact. We don't pay the full cost for. You know, oil's buried sunshine.

It's been under the ground for millions of years, and we've used it all up. Our generation will effectively have taken that opportunity away from future generations by using all that buried sunshine. Charlotte Williams, today we take manufacture of plastics for granted, but when did chemists first learn to synthesise polymers in that way? I was very shortly after studying as proposals that polymers, were macromolecules. In the 1930s, chemists at DuPont, most notably Wallace Carruthers,

began working on a program to make synthetic fibres, and they were able to make the first nylons. These are really useful materials, initially used a lot in clothing, but later on, much more important in the Second World War for materials for parachutes and ropes. And at the same time in the United Kingdom, researchers at ICI were developing the synthesis of polythene. And again, this was quite a critical material for the Second World War as it enabled the development of radar. So they already knew that wool was a polyamide that was joined together by these amide bonds. And chemists knew how to make amide bonds, which you get from reacting an acid and an amine. So basically they did cookery.

They went to the shelf, took down diacids and diamines, mixed them together to make the polymers, learned that you had to have exactly the right ratio of acid and amine to make a long chain polymer. And then once they'd made the polymers, worked out whether they'd form fibres or not. So that happened in Caruthers' group. The polythene, the initial discovery was an accident. Chemists were working on the properties of the gas that the polymer was made from. and measuring the pressure as it went through tubes and then one day they came back there was no pressure and so being good scientists they opened up the tube

to see where the pressure had gone and the gas had turned into a solid that solid was polyethylene and then they worked out how to join the polyethylene together how to make different kinds of polyethylene and now modern catalysis means that you can have very precise control over the synthesis of these very simple molecules

made from olefins. Can you tell us, Thini, and give us a sense of the range of applications for synthetic polymers? Well, Tony's mentioned how many different examples there are just in this room, but these are all, if you like, quite homely kind of things, but they also turn up in a lot of the more sort of modern technologies, if you like. Tony mentioned the thin layers on screens for computers and TVs and things.

There is a big program trying to work out what you might be able to do with them in a sort of medical setting. So that if you are going to try and replace parts of our body, can you do something involving polymers, plastics to make a stronger bond in our hip perhaps or a stent in our to open up an artery, things like that. And personally, I would like to think that, to come back to the Berritt Sunshine, that we will move away from using the oil we do have to make sort of cheap throwaway stuff, which then we have to worry about landfill and move to these much higher tech applications where this is the only route we might be able to go.

So you think the macromolecules are taking us to places that we simply couldn't have got to without, an understanding of them. Yeah, my favorite example is your mobile phone. So for your mobile phone to work, you needed deep insight from physicists in quantum mechanics. But to bring it to life, you need polymer chemistry. So to write in silicon on a chip, you actually need to have polymer chemistry

because in order to make a silicon chip that will run a phone or a computer, You have to write atoms through a mask, and the mask is made from a polymer. Can we, Charlotte Williams, go concentrate a bit more on this idea of using crude oil, which has been brought up once or twice in the conversation so far, and time is very emphatic that we more or less spent it. What are the alternatives to producing these polymers then if we run out of the oil, which seems to be essential to the process at the moment?

There are a number of alternatives. In some senses, this returns to the very early days of polymer chemistry because you can use plants as the raw material to make polymers, just like those early chemists did when they were developing things like Bakelite. But the approach being taken nowadays has the benefit of 100 years of chemistry, development and understanding of macromolecules. So people are looking at using starch, cellulose as the raw materials from which to make the modern materials with high degrees of

transparency, good elasticity, high strength for a range of applications. One material that's leading the way is a polymer based on lactic acid, known as polylactic acid. Lactic acid is a naturally occurring material and so this polymer can be made by harvesting of things like corn or sugar beet efficient chemical. syntheses to transform it into the polymer and then at the end of its lifetime with some heat and some water vapour it can it can degrade. And there's another I think intriguing example of using bacteria to produce plastics and this was a technology that's been known about for quite a long time. ICI developed it to a point where they were producing large sort of vats of these bacteria

are producing this material they called biopole. And it was marketed and then it was sold on to Monsanto, but it was just at that time not economic. And I think it comes back to the argument about what should we be doing with our oil. Because biopole was a perfectly good plastic, it was biodegradable, but it was much more expensive than the conventional plastics made from oil. And so it failed as a technology simply in terms of the economic. Is this part of the drive to find how to produce biodegradable plastics?

It's undoubtedly it could be part of that equation. I mean, there are many things that factor in. At the moment, well, there is definitely a move away from using plastic bags and supermarkets now have these sort of natural fibre bags and things. But before we got to that point, one of the things that was done was to incorporate starch, for instance, into the polythene. So that the bag had a lot of the properties of polythene, but because there was quite a lot of starch in there,

which is water soluble. If you leave it lying around slowly, the bag will disintegrate. Now, that's not quite biodegradable because the polythine bits are still lurking, but you no longer have that sort of big bag that floats around in the breeze. It's in small fragments.

And you need to worry about, if you are going to replace materials, you need to be very careful about what you're doing. So if one's going to use a Hessian bag over and over again, you need to use that bag 130 times to have saved any energy over using a carrier bag once. So the energy content of one of those kind of, you know, I'm good to the environment shopping bags,

is 130 times higher than the energy content of a disposable plastic bag. Now, I'm not making a value judgment here. But what conclusion do you draw from that? Well, okay, so I'll make a value judgment now. You need to either reuse carrier bags over and over. So if you get 10 uses out of a carrier bag, you'd need to use the fabric bag printed up with,

I'm Good to the environment, 1,300 times to be ahead. So we need to be cleverer about how we use plastic and less emotional about the choices we make with materials. Yeah, I was going to say the same thing. I think that's right. It's quite an emotive subject. And in order to fully decide which is the right material to use,

you need to consider both the raw material you're using, how you're using the material, what happens to it at the end of its life, how it's disposed of. And only through answering those specific questions, can you come up with a decision about which is the better material to use? Do you feel there's a sort of public resistance to what you think is the sensible course? I don't think so. I think that the public are keen to use new materials and to have new materials develop from alternative feedstocks,

but that it's important that we fully explain the right ways to use them, the right ways to dispose of them. Can you give us the major differences between natural and synthetic macromolecules before we move on? To a large extent it's the building blocks, but as we've heard, there is a sort of continuum. So natural, I guess people would interpret as being produced in nature, but you can synthesize the same molecules in a test tube. If you know what you're aiming at, you can find ways of doing it. So the difference is really just whether it's done in a factory, in a man-made way,

or we are using a natural process in our bodies or in plants. One quite interesting difference is that very often the man-made materials aren't perfect. They have a range of different molecular weights, a range of different chain lengths, whereas very often the natural materials are perfectly synthesized. Well, that's certainly true for proteins, but for polysaccharides, we have the same variability in plants, in fact. And the polymer that's made is made generally by another polymer. polymer. So the machine that actually makes the polymer is a polymer itself. You end up in a

situation of which came first, the chicken or the egg, but that's the question of the origin of life and polymer molecules were there right at the beginning of the origin of life because life is made from polymers. Can we go to something more specifically? Can I talk about degenerative diseases and how polymer's macromolecules study is leading to changes in that area? Okay, so in something like Alzheimer's, people will know that in the brain of a patient who's died of Alzheimer's, there are these so-called plaques. And these plaques are regions of protein molecules which have stuck together. So there are different proteins for different diseases in Alzheimer's. It's a protein known as abeta, which is a bit of another protein called amyloid precursor protein.

In Parkinson's, it's synuclid. But as a physicist, what interests me is the fact that you find similar kinds of states of aggregation of these proteins, which have moved from being in their native structure. We talked at the beginning of the program, but proteins typically being globular. But they can misfold, they can start to unfold in the degenerative diseases. It's assumed that this is because something in the control mechanism breaks down. So the proteins are no longer blobby spherical things, but they're partially. unfolded and that means that they can stick together in the ways that Charlotte described. They can come together to form sheets known as beta sheet rich plaques and that's what's happening in the brains

of patients with Alzheimer's. Now one of the interesting things is this seems to be quite generic. There are a lot of proteins which can do that and people have been studying these in test tubes to try and understand what it is that causes these kind of aggregates to form and therefore what you might be able to do to intervene. And obviously the real challenge is trying to identify patients who are at risk before these diseases have sort of taken over their lives. And we're quite a long way from that. And understanding the plaques themselves may not be the right solution because the toxicity, if you like, the thing that is ultimately going to kill you may happen long before we can see these visible quite large-scale aggregates in the brains of patients. So there's a huge effort being directed

at trying to understand why the proteins misfold in the first place and what it is that is actually the toxic species and there's still some debate about that. So one of the difficulties is getting to the root of the history of the disease. Indeed, because usually you only know that someone's got it when you do a post-mortem. I mean, classically, that is the way of identifying definitively that this person had Alzheimer's in particular.

and it is a lot of people say my whatever it is I know someone with Alzheimer's or whatever it is and speak about it quite common as if it were something that is well known and it's easy to recognise they speak that way including me well there are many kinds of dementia and I think clinicians would distinguish where the plaques are which particular protein is involved

there are a whole family of them which manifest themselves in similar ways in the loss of memory, that kind of empowerment, but there may be specific differences. But as I say, very often, they have the same generic cause. Tony Ryan, one of the key areas of polymer research focuses on how to harness the energy of the sun. Now, you yourself are involved in that.

Can you tell us where you are with it? Well, actually, Atheney and I worked together on that project. I know, we didn't want to let that secret out, but you've gone to, you've gone to, you've gone, you've gone, You've gone and blown it, Tony, never mind. And the thing about harvesting the energy from the sun is there are many different ways to do it. So you can boil water using a mirror. And that happens, you know, if you go on holiday to the Mediterranean,

you often see water heaters on the tops of roofs. You can capture the energy from the sun in something that's made of an inorganic semiconductor, a silicon chip. and they can be made very efficient. In fact, you can make silicon chips or 3-5 germanium nitride chips that work at very, very high temperatures. You have a big mirror to concentrate the sun's energy on this tiny chip that then converts the energy into electricity.

And it does that by separating an electron because electricity is the movement of electrons. In polymers, what we do is, rather than having things that are very highly efficient, efficient. We make low efficiency materials so they're not very good at converting the sunshine into electricity. They're still semiconductors

they behave in exactly the same way, but they're made from plastic. Because they're made from plastic you can process them into large areas so you can make cheap large area devices as opposed to very expensive

small area devices and you can only do this with macromolecule. Well you can, yeah, it's essentially you can only do it with macromolecules because the properties, you know, they'll go into solution, you can dissolve them, you can print with them as if you're printing with ink. You can use all the, rather than having to do things at very high purity, ultra-high vacuum processing, you can use a off, you could even, we're even working on being able to process them in the open air. So you literally print a solar cell in the same way that you might print a newspaper. But are you talking about something which will lead to this planet, being able to sustain its energy on solar energy properly conducted,

if I can use that word, in the way you're experimenting? I think we're always going to need an energy mix. So we'll always use hydroelectric power. We'll use wind power. We might continue to use nuclear power for a long, long time. but solar energy solar harvesting in its many different forms will be part of that energy mix and plastic solar cells will be a big part of that because they'll be cheap, flexible, easy to apply. Essentially you could think about wiring them up with a staple gun and copper tape

and then running a house on 9 volts rather than running a house on 240 volts. On a scale of 1 to 10, as the other part of this research group we suddenly have in the studio, an advanced research group, how far are you to get into where you want to be in this solar research? I think we've learnt an awful lot about what needs to be done. So the kinds of materials that work well have been identified. And to some extent, I think the trick now is understanding the processing to get an efficient device that you can make in these large areas. I think it's very important that we have to be able to do this, as Tony says, in air and things like that. So we know what we need to do. We haven't quite got there yet. Charlotte Williams is about to dive in. I disagree that we understand perfectly the structures of the polymers that will form the most efficient photovoltaics.

The current materials don't match the solar spectrum particularly well, and there are problems with electron transport. So there's certainly lots and lots of chemistry to be done in terms of development. I'm absolutely delighted that you're flatly disagreeing with him. I'm not flatly disagreeing. I think these are very promising materials, but we have a long way to go. And it's great to get that view that you have to have the molecules right. So you need to match the solar spectrum.

So you need to get the same range of energy out, absorb the whole energy out of the sun. But you also have to organise the molecules in the right way. And that's at the nub of the science of macromolecules. You have to get the chemistry right in detail. and you have to get the organisation right of many, many molecules. And I think what's interesting is that there are many groups worrying about the bang-gat kind of aspect and far fewer worrying about the processing, which is where Tony and I come in. The band-gap being the electronics and the processing being making the right device.

And actually this theme of the chemistry and the ordering is true of whatever application of polymers you look at. It applies just as much in medicine as it would in electronics or just as much in making a strong, tough material as it would for future energy conversions. Can you tell us about the catalyst and why it's so important, Charlotte? Yes, so a catalyst enables the polymerisation to occur more rapidly, and so ultimately it controls the economics of the process. But much more than that, it can be used to control with high degrees of sophistication, the ordering of the monomers and the packing of the chains.

So one of the themes of catalyst research has been to try and understand how the structure of the catalyst affects the properties of the material you make. For example, in the case of polylactic acid that we talked about earlier, by selection of the right catalyst, you can produce fibres that can be used to make clothes that can be ironed. But if you don't choose the catalyst correctly, the fibres would melt under the action of an iron. Tony, in what otherwise, Tony, Ryan, are macromolecules being used in medical research? Can you give us a brief survey?

So I'm going to pick up the same molecules that Charlotte was talking about, polylactic acid. And it's used in tissue engineering to make scaffolds. And we use the word scaffold in exactly the same way that everyone uses the word scaffold. It's something that you build on, that you build from. And so we make nanofibers, fibers that are a thousand times thinner than theirs on your head,

that cells will grow on and are using them to make synthetic skin and synthetic cornea. And then the body's mechanism, because lactic acid is a metabolite, the body's mechanism then dissolves the polylactic acid and the cells take over and you've re-engineered a new piece of tissue. What sort of developments do you expect to see in the future, Theney?

I think these are very much the, the kinds of things that people are going to be looking at. There was this wonderful example in the past year about someone making a synthetic windpipe where they created exactly this kind of scaffold and then used the patient's own cells to populate that scaffold and replace the trachea. And that seems to be very successful.

And I think it's a question of getting materials that can be made into the right shapes that are compatible with cells and which will then naturally be degraded in our bodies so we aren't left with foreign bodies. I think that is a hugely exciting area. And with the way people are learning more about stem cells, for instance, I think we will only see more things happening.

And with stem cells, it's very interesting because if you have different substrates, they will differentiate into different kinds of cells. So you've got a huge scope to tailor these things for different applications. Final word from Tony. The thing that I'm really looking forward to is a way of using polymers. and the things we know about polymers, to store energy, to make our own, on economic terms, energy storage mechanisms.

If we are going to run the world on sunshine, then we're going to need a way of storing the energy to pass on to the night or to the next year. And so developing mechanisms where we can capture the sun's energy, use a catalyst to make a macromolecule to store that energy, then use another catalyst to break the macromolecule down to release the energy when we want it, then we will have really used

the power of macromolecules for the long-term benefit of mankind. Well, thank you very much. For me, that was a whirlwind tour. And how, thank you, Athena Donald, Charlotte Williams, and Tony Ryan. Next week, I'll be looking at the history of the written word from 3,500 BC to today.

It's a week of programmes every morning starting on Monday at 9 o'clock. Thank you for listening, and a happy new year. If you've enjoyed this BBC podcast, why not try others such as The Forum, the discussion program about global ideas. To find out more, visit BBCworldservice.com slash forum.