Nadeen Chahine and Clark Hung are working to develop a "living" knee implant that could be a better option for some patients in need of knee replacements. (Image credit: Columbia University) Imagine getting a knee replacement made of living materials rather than metal and plastic. Researchers at Columbia University and the University of Missouri are working to make that vision a reality. Their 3D-printed knee implant, called NOVAKnee , is composed of a biodegradable scaffold packed with stem-cell-derived bone and cartilage. The idea is that, once inside the body, the scaffold will gradually disappear as it's replaced by new bone and cartilage that will integrate into the patient's skeleton. NOVAKnee could be a better option for these patients. The implant has been tested in lab mice, in experiments where a tiny version was placed beneath the animals' skin to see how the body reacted.…