Forty years ago, plastic surpassed steel as the most widely used material in the world. Sure, the affordable and malleable polymers have brought plenty of convenience to modern life (Tupperware! Teflon! Velcro!) as well as taking on more-vital roles, in airplanes, cars, and smartphones. There's a catch, however: Unlike many of the metals it replaces, plastic is really hard to fix; even invisible fractures can compromise its strength. A new class of smart plastics can heal breaches all on their own, to mend cracked phone screens or stitch up airplane wings.

Nancy Sottos helped pioneer this field in the '90s. Her team at the University of Illinois at Urbana-Champaign has developed composites that can repair themselves using a range of methods.