Fig. 3: Stiffness and extensibility of DN polyacrylamide/alginate (PAM/Alg) hydrogels.

The grafting ratio of TZ-PAM and NB-PAM is fixed at 2.5% unless otherwise specified. a Dependencies of storage (\(G^{{\prime}}\), solid lines) and loss (\(G^{{\prime} {\prime}}\), dashed lines) moduli of completely crosslinked single-network PAM, single-network alginate (Alg), and double-network PAM/alginate hydrogels on oscillatory shear frequency. The composition of a crosslinked hydrogel is denoted as PAM_xAlg_y, where x is the concentration in (w/v)% for PAM consisting of equal amount of TZ-PAM and NB-PAM, and y is the concentration of alginate. b Equilibrium shear moduli of single-network PAM, single-network alginate, double-network PAM/alginate hydrogels. c Photos of PAM₁₀, Alg₂, and PAM₁₀Alg₂ hydrogels under uniaxial tensile tests at a fixed strain rate of 0.02/s. For each formulation, the left, middle, and right panels are, respectively, captured at the beginning of the tensile test, right before breaking, and right after breaking. Samples are 13 mm in length and 2 mm in width of the center part. d Stress–strain behavior of hydrogels. Dashed red line: a PAM₁₀Alg₂ double-network hydrogel made from TZ-PAM with a grafting ratio of 2.53% and NB-PAM with a grafting ratio of 0.63%, which is denoted as PAM₁₀^1/4Alg₂. e A two-parameter (\(G\), \({\epsilon }_{f}\)) diagram-of-state that outlines the mechanical properties of all hydrogels formulations in (d). Empty circle corresponds to the hydrogel PAM₁₀Alg₂ with mismatched TZ and NB grafting ratios in (d), which is denoted as PAM₁₀^1/4Alg₂.