Would you live in a city made of bone?

The cities of today are built with concrete and steel - but some Cambridge researchers think that the cities of the future need to go back to nature if they are to support an ever-expanding population, while keeping carbon emissions under control. Just because we can make all of our buildings out of concrete and steel doesn't mean we should. But it will require big change - Michelle Oyen Between them, concrete and steel are responsible for as much as a tenth of worldwide carbon emissions. Before they ever reach a construction site, both steel and concrete must be processed at very high temperatures - which takes a lot of energy. And yet, our cities are completely dependent on these two unsustainable materials. "I fly back and forth a lot between the UK and the US, and I'd been harbouring a lot of guilt about the effect that had on my carbon footprint - I'd always assumed, as many of us do, that air travel is a huge contributor to carbon emissions," says bioengineer Dr Michelle Oyen of Cambridge's Department of Engineering. "But the truth is, while the emissions caused by air travel are significant, far more are caused by the production of concrete and steel, which of course is what most cities are built from." So what does that mean for cities of the future, as more and more of us live in urban areas? How can we continue to build while reducing carbon emissions? Whereas some researchers are investigating ways of producing steel and concrete in more energy-efficient ways, or finding ways of using less, Oyen would rather turn the tables completely, and create new building materials that are strong, sustainable and take their inspiration from nature.