As Tom Brady and other athletes can attest, you really, really want to avoid tearing your knee's anterior cruciate ligament (ACL). It can't heal up, and the tendon graft used to reconstruct it will likely leave you with permanent pain. Victims may have a much easier time of things if Northwestern University's nanotechnology-infused ligament becomes a practical reality, though. Their remedy combines calcium nanocrystals (like those in your bones), a porous biomaterial and strong polyester fibers to replace your ACL without having to perform grafts and leave you in continued agony. Both the artificial implant and the bone integrate with each other, stabilizing the knee in a way that both lets you move more naturally and spares you from losing some muscle.