Differentiation of human MSCs. Characterization of MSCs by differentiation assays. One donor is presented. Row 1, high (right) and low power (left) micrographs of osteogenic MSCs stained with Alizarin Red S for calcium. Row 2, high (right) and low power (left) micrographs of adipogenic MSCs stained with oil red O for lipid. Row 3, high (right) and low power (center and left) micrographs of toluidine blue (purple) stained sections of MSC pellets induced to form chondrocytes and cartilage. All donors were assayed for adipogenesis and osteogenesis with the exception of chondrogenesis, where 2 donors were assayed.