Bioengineer Dr. Michelle Oyen of Cambridge's Department of Engineering notes that 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." Her team are looking into biomimetics -- looking to replicate biological processes in the lab. Recently they've made artificial samples of eggshell and bone in a process that could be easily scaled up -- and all at room temperature.
The benefits come from the composition of these bio-materials. Bone is made of roughly half protein and half minerals: the former gives it structural stiffness and hardness, while the latted gives it toughness and resistance to damage. (There's also the bonus that bones are able to heal themselves from light damage.) Eggshell leans more heavily towards mineral at roughly 95 percent, but that small bit of protein still ensures it's incredibly tough, given how thin it is.
Your eggshell condo isn't going to be ready this decade, however. The collagen that Oyen's team needs to make these materials comes from natural animal sources -- more research is needed to see whether non-animal-derived or even completely synthetic proteins could work in place of natural collagen: the part that minerals bind with.
Talking to the University of Cambridge, she added: "Another issue is the construction industry is a very conservative one. All of our existing building standards have been designed with concrete and steel in mind. Constructing buildings out of entirely new materials would mean completely rethinking the whole industry. But if you want to do something really transformative to bring down carbon emissions, then I think that's what we have to do."