Fig. 4.

Mesenchymal stem cell (MSC) differentiation on elastic substrates. A) Morphology of naive, low passage MSCs (upper panel) 24 h after plating on PA gels of different stiffness closely matches that of cell lineages found within each microenvironment. Naive MSCs are initially small and round but a dominant fraction indicated here (lower panel) develops increasingly branched, spindle, or polygonal shapes within days of plating when grown on matrices with respective elasticities of 1 kPa, 11 kPa, and 34 kPa. Results for mitomycin C treated cells are shown with diagonally-hatched bars. Scale bar is 20 μm. B) Differentiation of MSCs directed by substrate elasticity elucidated by key marker proteins. The neuronal cytoskeletal marker (β3 tubulin is expressed in branches (arrows) of initially naive MSCs (>75%) and only on soft, neurogenic matrices (first row). The muscle transcription factor MyoD is up-regulated and nuclear localized (arrow) only in MSCs on myogenic matrices (second row). The osteoblast transcription factor CBFα1 (arrow) is likewise expressed only on stiff osteogenic substrates (third row). Scale bar is 5 μm.