Figure 2.

Extrusion bio-inks for engineering stiffness gradient microenvironment. Scheme depicting the bioprinting experiment of (A) two-dimensional (2D)- and (B) three-dimensional (3D)-graded stiffness. The colored gels reveal the changes in hydrogel compositions from (C, E) stiff (red) to soft (blue) and (D, F) medium (green) to soft (blue). The mechanical properties of (G) 2D and (H) 3D prints have been analyzed by indentation tests; the E modulus equals the indentation elastic modulus. Error bars show a standard deviation of n = 3. Scale bars: (C, D) 10 mm, (E, F) 1 mm^[75].