Tissue engineers have made great strides in growing bone parts in the lab, but it is proving much more difficult to replace whole sections of leg or arm bones, which sustain constant pounding. Researchers at Rice University have developed a technique for growing bone tissue strong enough to withstand the stresses of everyday activity. Conventional bone-tissue engineering involves replacing lost bone with a biodegradable polymer scaffold seeded with cells. As the polymer degrades, new tissue develops. But in load-bearing parts of the skeleton, cells are constantly breaking down and forming new bone in response to mechanical stimuli. If the polymer scaffold placed in a patient’s leg is too weak, the material falls apart under this stress. To reinforce their scaffold material, Rice bioengineer Antonios Mikos and chemist Andrew Barron added nanoparticles of alumoxane (an aluminum-based compound) to a photosensitive polymer. Shining light on this blend spurs the nanoparticles to fix themselves to the polymer chains. The resulting material’s compressive strength is three times that of the polymer alone. Mikos hopes to start testing the material in rabbits this summer.