Antifreeze and Self-Healing Hydrogels with Hyaluronic Acid Functional Cellulose Nanocrystals and Proline for Flexible Sensors

PCHZF hydrogel shows 88.2% self-healing and 2.2   MPa fracture stress. • The sensor has rapid 207.3   ms response and captures subtle body movements. • Cellulose nanocrystals are modified to increase surface functional groups and enhance their freeze resistance. • The PCHZF hydrogel-based flexible sensors can still function effectively at -30℃. In recent years, hydrogels have emerged as viable candidates for soft conductors in wearable flexible electronics, due to their distinctive properties including high water content, excellent biocompatibility, and adjustable mechanical properties. However, the crystallization of H 2 O molecules within hydrogels at low temperatures leads to significant deterioration in their toughness and mechanical strength, severely restricting their practical applications in cold environments. Cellulose nanocrystals (CNCs), rod-like nanomaterials with high crystallinity extracted from natural cellulose, have attracted increasing attention due to their outstanding mechanical properties, biocompatibility, and environmental friendliness. In this study, hyaluronic acid (HA) was adsorbed onto the surface of CNCs via hydrogen bonding, forming CNCs@HA nanomaterials. And then zwitterion proline (ZP) and CNCs@HA were incorporated into an acrylic acid-based hydrogel system, resulting in the formation of a novel freeze-resistant and self-healing nanocomposite hydrogel PAA-CNCs@HA-ZP-Fe 3+ (PCHZF). The excellent properties of PCHZF can be attributed to the strong hydrogen bonding network formed among water molecules, CNCs@HA, and ZP molecules. These intermolecular interactions effectively inhibit the crystallization of water and maintain the integrity of the hydrogel matrix at low temperatures. Its compressive strength reaches 2.2   MPa, with a remarkable self-healing efficiency of 88.2%, and it can even achieve reliable sensing performance at extremely low temperatures.