Here’s a nice summary of the research from the WSJ:
Dr. de Peppo and his colleagues used a method known as reprogramming to transform human skin cells into embryonic-like stem cells, which can become all other cells in the body.
When certain chemicals were added, the stem cells became cells that can go on to form bone. The bone cells were placed on a scaffold, a sort of frame where they could grow and achieve a three-dimensional structure. The scaffold had been made by washing a cow’s bones in chemicals, which left behind a collagen-based structure.
After the scaffold was seeded with the bone cells, it was put in a bioreactor, a tabletop device that provides nutrients and removes waste. As a result, bits of bone, each about 16 square millimeters (0.025 square inches) in size, grew on the scaffold.