In her lab at Cambridge University, the bioengineer Michelle Oyen has been busy making samples of artificial bone and eggshells. The samples are only centimeters in length, but she hopes that they’ll someday make up high-rises and skyscrapers. And in that way, cities of the future will emulate one of the most ingenious designers out there: nature. That future is still decades away, but scientists like Oyen have been studying how processes found in nature—the…