Robust biopolymer based ionic-covalent entanglement hydrogels with reversible mechanical behaviour

Emerging applications of hydrogels such as soft robotics and cartilage tissue scaffolds require hydrogels with enhanced mechanical performance. We report the development of a robust biopolymer based ionic-covalent entanglement network hydrogel made from calcium cross-linked gellan gum and genipin cross-linked gelatin. The ratio of the two polymers and the cross-linker concentrations significantly affected the mechanical characteristics of the hydrogels. Hydrogels with optimized composition exhibited compressive fracture stress and work of extension values of up to 1.1 + 0.2 MPa and 230 + 40 kJ m(-3) for swelling ratios of 37.4 +/- 0.6 and 19 +/- 1, respectively. The compressive and tensile mechanical properties, swelling behavior (including leachage), pH sensitivity and homogeneity are discussed in detail. Fully swollen hydrogels (swelling ratio of 37.4 +/- 0.6) were able to recover 95 +/- 2% and 82 +/- 7% of their energy dissipation (hysteresis) at 37 degrees C after reloading to either constant stress (150 kPa) or constant strain (50%), respectively.