Recoverable and Self-Healing Double Network Hydrogel Based on κ-Carrageenan.

Combining an ionically cross-linked κ-carrageenan network with a covalently cross-linked polyacrylamide network, we have fabricated a κ-carrageenan/polyacrylamide double network (DN) hydrogel using a one-pot method. The resulting DN hydrogel exhibited a high elastic modulus of 280 kPa and a fracture energy of 6150 J/m2. A model has been proposed considering unzipping of double-helical aggregates and dissociation of double helices of κ-carrageenan, which could well interpret the continuous fracture process of the first κ-carrageenan network and the toughening mechanism of the physically and chemically cross-linked κ-carrageenan/polyacrylamide DN hydrogel. Owing to the thermoreversible nature of κ-carrageenan, the DN hydrogel also exhibited the excellent recoverable property. For example, the elastic modulus and energy dissipation could be recovered to 100% and 98% after the deformed and relaxed DN samples were stored at 90 °C for 20 min. Furthermore, the temperature-dependent sol-gel transition is also related to the self-healing property of the DN hydrogel.