Fabrication of anti-freezing and self-healing nanocomposite hydrogels based on zwitterionic proline and cellulose nanocrystals

Self-healing hydrogels with three-dimensional network cross-linked structure and adjustable properties have been considered as smart materials with promising multi-purpose applications. However, traditional self-healing hydrogels face the loss of mechanical properties at sub-zero temperatures, which may limit their application in various fields to some extent. In this manuscript, functional polydopamine (PDA) was successfully chemically modified on the surface of cellulose nanocrystals (CNCs) by self-oxidation polymerization in an alkaline environment. The nanocomposite hydrogels with self-healing and anti-freezing properties were successfully designed by introducing zwitterionic proline (ZP) and CNCs@PDA into the cross-linked network structure of gellan gum/ polyacrylic acid (GG/PAA). When the ZP ratio increased, the anti-freezing performance of hydrogels was significantly enhanced. Even at -30 degrees C, the GG/PAA-CNCs@PDA-ZP-Ca2+ (GP/CP/ZP/Ca2+) nanocomposite hydrogels still maintain excellent stress (2.7 MPa) and high self-healing efficiency (82.9%). This work proposes an effective solution to prepare flexible hydrogels with anti-freezing capability, which will extend the temperature range of the flexible material and broaden the application area.