Fig. 5.

Images of cell response after encapsulation within hydrogel gradients. (a, b) Epi-fluorescence images of cells stained with the live (a) and the dead (b) stains at the soft end (≈ 10 kPa) of the gradient 1 d after encapsulation. (c) Phase contrast images of cells in soft end (≈ 10 kPa) of hydrogel gradients after 1 d. Spherical objects are cells. (d) Phase contrast micrographs of mineral deposits at the stiff end (≈ 300 kPa) of the gradient stained with Alizarin red S after 42 d. Dark spots are indicative of mineral deposits. Scale bar in (a) applies to (a–d) and equals 0.1 mm. (e) Photograph of gradient hydrogel after 42 d culture. Note that the hydrogel appears white at the stiff end (high modulus) due to the presence of large amounts of mineral deposits. The mineralization occurs in normal medium without osteogenic differentiation supplements.