In hopes of producing concrete structures that can repair their cracks, researchers from Drexel University’s College of Engineering are putting a new twist on an old trick for improving the durability of concrete. Fiber reinforcement has been around since the first masons were mixing horsehair into their mud. But the Drexel research team is taking this method to the next level by turning reinforcing fibers into a living tissue system that rushes concrete-healing bacteria to the site of cracks to repair the damage.