Antifreeze proteins and surface-modified cellulose nanocrystals for designing anti-freezing conductive hydrogel sensors.

Antifreeze proteins (AFPs) are a type of protein capable of inhibiting ice crystal growth, lowering the freezing point, and protecting organisms from cold-induced damage. In this study, cellulose nanocrystals (CNCs) are chemically modified to enhance the hydrogel's performance. The synergistic effect with AFPs further regulates its mechanical properties, antifreeze performance, and high sensing sensitivity. First, based on the principles of mussel-inspired chemistry, dopamine (DA) was introduced to increase adhesion and chemical crosslinking points, successfully modifying zwitterionic proline (ZP) onto the CNCs surface to obtain cellulose nanocrystals@polydopamine@zwitterionic proline (CNCs@PDA@ZP). Subsequently, CNCs@PDA@ZP and AFPs were incorporated into a multi-component network of polyacrylic acid/guar gum (PAA/GG) and FeCl3 to construct an antifreeze, self-healing nanocomposite hydrogel-based flexible sensor. Through the synergistic effect of its components, along with AFPs inhibiting ice crystal growth by binding to H2O, the hydrogel achieves an 81.7 % self-healing rate in 1.3 h at -20 °C and a fracture stress of 3.0 MPa. Additionally, the hydrogel's high sensitivity (GF = 4.0) enhances its suitability for motion detection in flexible sensors. This work provides a method for modifying nanomaterials and contributes an approach for antifreeze, self-healing nanocomposite hydrogels.