Differentiation assay of mesenchymal stem cells for osteogenic, adipogenic and chondrogenic lineages. (a) Osteogenic differentiation. Note calcium deposits stained with Alizarin red. (b) Adipogenic differentiation. Note the intracellular presence of lipid droplets stained with Oil red. (c, d) Chondrogenic differentiation. (c) Toluidin blue staining. Note the presence of metachromatic areas in pink (red arrow) indicating the presence of extracellular matrix containing proteoglycans. (d) Alcian blue staining. Note the presence of areas in blue indicating the presence of extracellular matrix containing proteoglycans beyond the presence of gaps (red arrow) possibly containing chondrocytes. Bar = 50 μm.