The concrete industry produces almost five percent of manmade carbon dioxide worldwide, and waste from demolition is also ecologically unfriendly. Solutions to the problem may lie with some new, bio-inspired building materials.
‘There are so many things that people do that are incrementalist,’ says bio-engineer Dr Michelle Oyen from Cambridge University’s Department of Engineering. ‘Incrementalist approaches say “ok we need to reduce our carbon emission and therefore we’re going to make more efficient powerplants.” Whereas I'm saying throw the current wave thinking about things completely out the window and let’s do something completely different. If you want to solve big problems, sometimes you have to have bold solutions.’
BONE AND EGGSHELL
Dr Oyen is explaining her research on artificial bone and eggshell, which could be used for low-carbon building materials. Since she spoke about it at the Cambridge Science Festival earlier this year, interest in her work has rapidly accelerated, ‘the last six months since I spoke at the festival has been kind of insane,’ she says, ‘because there has been a lot of interest in this, I have done a lot of interviews, and there’s been a lot of articles written.’
It’s a project that’s likely to prompt interest in the construction industry. Manufacturing concrete requires a huge amount of energy and releases gas emissions, while disposing of it as waste also has a significant impact.
Two years ago Dr Oyen was attending a materials research society event in Boston, which included a visit from an environmental minister from Germany. Hearing about the large carbon footprint made by steel and concrete inspired Dr Oyen to shift the focus of her research, and she began to explore alternative natural and bioinspired materials whose formation don’t require such a large input of energy.
BALLET AND BIOENGINEERING
Dr Oyen’s scientific journey began as an undergraduate studying material science and engineering working on more traditional material science. She jokes about the personal reasons behind her research choices. ‘Ever since I was a teenager, I’ve always had real problems with my joints, as a ballet dancer,’ she explains. ‘Eventually I had some stress fractures in my feet and have some long-term arthritis problems. I was in my undergraduate final year, and realising that there were ways that you can use engineering to solve medical problems, I was very selfishly thinking maybe I could fix my own knees and my own feet, and so that’s when I got interested in it!’
She had already committed to doing a PhD and had received a scholarship for doing it, but she was able to shift focus and convert it from more traditional engineering into bioengineering.
She did her PhD on bone. ‘Part of that involved the very first studies that I did on artificial bone material and it was something that I was really excited about,’ she says. When Dr Oyen got her post at Cambridge she started up her own group and research. ‘At some point between the end of my PhD and the start of my job I started realising that making artificial bone was interesting not just for medical applications – bone is a really good structural material.’ Dr Oyen has some sense of this already, her PhD supervisor had a PhD in bioengineering and was a dentist. ‘When I was working in my PhD, we were looking at the bone in the jaw where the teeth were anchored in – that was when I first got to work with artificial bone or artificial bone-like materials, and then that became a real focus for me.’
They are currently working with a bone-like material and an eggshell-like material – they are both composites of minerals and proteins, albeit in different ratios.
They have had more success in making the artificial bone partly because of the proportions of mineral and protein are roughly equal. The bone’s stiffness and hardness is derived from the mineral, its toughness comes from the protein. Bone’s self-healing property would make it an attractive material to design with.
The eggshell-like material is 95 percent mineral to 5 percent protein, Dr Oyen says that though it ‘has the right composition it hasn’t coalesced, it is more of a work in progress.’ They realised they needed a better understanding of the natural materials, so devoted less time to the synthesis of the new material. ‘We’ve been studying natural eggshells a lot in the last six months.’
The ubiquity of eggs as an everyday object means it’s easy to miss its extraordinary properties. ‘Chickens can basically lay a new egg everyday, you go from basically a soft squishy thing to completely mineralised egg shell in about 18 hours, inside a chicken’s body. This is laying down material that you know intrinsically is very mechanically robust, just because of how hard you have to whack that egg against the counter or the side of the bowl or the pan to get it to crack. It’s really, really amazing stuff.’
FROM LABORATORY TO INDUSTRY
When making the artificial bone and eggshell, the mineral components are ‘templated’ directly onto collagen, the process takes place at room temperature. Not only does it take little energy to produce, but most importantly, in principle it should be easy to scale up. You can see some photos of the process in the laboratory here.
Dr Oyen has been discussing the implications of these biomimetic materials with a colleague in the manufacturing engineering group about scaling up and industrial use. ‘The volumes of samples that we’re making for laboratory research, are quite small,’ says, ‘whereas if you want to start talking about building things, you have to obviously scale up in quite a dramatic fashion.’