Entirely physical crosslinking strategy: pH-tuned double-network hydrogel composed of ferulic acid-ε-polylysine and polyvinyl alcohol.

This study reports a novel pH-tuned double-network hydrogel via an entirely physical crosslinking strategy. The hydrogel consists of a first network formed between ferulic acid and ε-polylysine via hydrogen bonding and electrostatic interaction, while a second polyvinyl alcohol network established through freeze-thaw cycles. The former network confers biological activities, while the combination of the two networks ensures mechanical strength. The hydrogels exhibit pH-tuned behavior, with significant differences in mechanical performance, swelling characteristics, and antioxidant/antibacterial activities among hydrogels prepared under different pH. Specifically, the hydrogel formed at pH 3 demonstrates 3.5-fold higher energy dissipation than that at pH 9, while the equilibrium swelling ratio reaches 235% at pH 1 versus 102% at pH 9. pH serves as a switch, modulating intermolecular forces by altering hydrogel component protonation states, thereby optimizing synergy within the double network. Such multifunctional hydrogels show promise for applications like active food packaging materials.