Improved Toughness and Stability of κ‑Carrageenan/PolyacrylamideDouble-Network Hydrogels by Dual Cross-Linking of the First Network

It is highly desired yet challenging to develop hydrogels with a combination of excellent mechanical properties and good stability for potential applications. Here we report κ-carrageenan/polyacrylamide double-network (DN) hydrogels with remarkable mechanical performances and high stability in water, which are achieved using zirconium ions to further cross-link the first physical network of κ-carrageenan by forming coordination complexes. Thus, obtained DN hydrogels in equilibrated state with water content of 83–91 wt % were highly transparent and showed tensile breaking stress of 1.5–3.2 MPa, breaking strain of 300–2200%, Young’s modulus of 0.2–2.2 MPa, and tearing fracture energy of 0.4–18.5 kJ/m2. We found that dual-cross-linking of the κ-carrageenan network, i.e., the coiled-coil junctions and the metal-coordination bonds, was indispensable for the combined mechanical properties and stability of these gels. Essential reasons were rationally discussed based on the results of control experiments. The st...