Eggshells, bones and the buildings of tomorrow
This week we're exploring biomimetics: how nature is inspiring the technology and materials of the future. But what exactly is it and how can an egg inspire a new type of building material. Izzie Clarke spoke to Michelle Oyen from East Carolina University, and formerly from Cambridge University...
Michelle - Biomemetics is imitating life. And you can take that imitation very literally and try to copy something that's in nature or you can take it more as being bio inspired and take ideas from nature and modify them a little bit with engineering principles to try and imitate life in a less literal manner.
Izzie - But we've been doing this for years. Leonardo da Vinci studied birds in the hope of enabling human flight and he made countless sketches of proposed flying machines and whilst he didn't quite make it, we got there in the end but it was in the 1940s, just after World War 2, when the field of biomimicry really developed.
Michelle - There were some very interesting professors who had a broad background in both physics and biology and he coined the term biomimetic at that time. The field grew slowly from then on into the 1970s and started to grow faster. It really took off in the 1990s when we started having tools of nanotechnology because a lot of the structures that we find in nature are nanometre scale. So when we had engineering approaches using nanotechnology it was much easier for us to imitate nature and so that's when the field of biomimicry really took off.
Izzie - Now we can copy nature in one of two ways…
Michelle - We can try to literally copy it, so make a direct imitation of something that we find in nature. So like a material like seashell or we can try and imitate the mechanisms by which that material is made in nature so we can use our inspiration by thinking about the materials. How they're made, how they're structured and then maybe not make a copy using the exact same components but in a similar fashion of putting the structures together in the same way.
Izzie - And this is what Michelle specialises in, using natural materials like bone and egg shell to create a new structural material.
Michelle - These are materials that have good structural properties good mechanical properties and, of course, they're made under essentially ambient conditions. Body temperature being just above room temperature. Both of those materials are composites in that they have multiple components: a mineral or hard component, and a protein or soft components. In nature these materials form by the mineral depositing on the protein component and so I've been studying how that works and then trying to think about imitating those sorts of materials for use in building structures. They might be good replacements for materials that we use in the building industry, such as steel and concrete, that are very effective but that have very very large carbon footprints. Especially as we've been seeing more and more development in some parts of the world like China. You have contributions to global warming from steel and concrete that's greater than the entire global airline industry and that's one of those things that would never occur to most people.
Izzie - In an ideal world we would mimic nature to create materials that don't require a high temperature to make them, unlike steel and concrete, and therefore releasing less carbon dioxide into the world. But why egg shells and why bone?
Michelle - Eggshell I became interested in because it has very good toughness so resistance to fracture. If you think about it an egg shell is 97 to 98 percent ceramic. It's like your coffee mug but the two to three percent of that isn't ceramic contributes dramatically to its toughness. And in fact it's really difficult to crack an egg open. You have to whack it against the table or against the edge of a pan pretty hard in order to open it up. For a material that's made under chicken temperature, an egg shell forms relatively quickly so you can go from basically zero to a solid egg shell in about 18 hours in the course of the chicken's body. Y ou have a material that forms very quickly has very good mechanical properties and of course hasn't had this energy intensive process that you would have in normal ceramic or concrete processing
Izzie - In addition to creating these artificial structures in ambient temperatures it's not like we're in a short supply of them
Michelle - Eggshell is made of calcium carbonate; so calcium and carbonates - Carbon and Oxygen. These are very abundant elements in the earth and that's why so much is made out of them. In fact egg shell is one calcium carbonate material but seashells are another calcium carbonate material, corals... These are all things that other researchers besides myself have been looking at from a biomimicry perspective. Your bones on the other hand are calcium phosphate but again calcium phosphorus oxygen and hydrogen. These are all very abundant elements in nature and so you don't have to go digging for them or mining for them. They're everywhere.
Izzie - At the moment Michelle has been able to grow these artificial structures a few centimeters at a time. So we've got a while to go before we're living in artificial egg shell shacks but what does the future hold?
Michelle - The work that I've been doing with biomimicry with both bone and egg shell thus far has relied on natural protein, natural collagen. There is a lot of collagen and that's essentially left over from the meat industry and so you can buy it in bulk quantities. But we're using that protein that came from some living cells living animals. So in fact the buildings that I would be building from the materials I'm making right now would not be vegetarian. So in fact one of the things that we're trying to do from a scientific perspective right now is to replace the need for that natural animal derived collagen with an artificial polymer that we can make in the lab hopefully something that is still environmentally friendly and we would have to work directly with the building industry to change the building codes in order to allow these sorts of materials to be adopted in structures where we allow people to go.