Humic acid-based anti-freezing and self-healing hydrogel flexible sensors with functional cellulose nanocrystals

Conventional hydrogels are prone to freezing in severe cold climates, limiting the application of hydrogel-based flexible sensors. This study proposes a strategic design that successfully prepares humic acid-based anti-freezing hydrogels via a one-pot method, which is named P-HPCB hydrogels. It combines modified cellulose nanocrystals (CNCs@BSA), natural organic humic acid (HA), the biomass component L-proline (L-P) and polyvinyl alcohol (PVA) through freeze–thaw cycles. By the way, CNCs@BSA was obtained by grafting bovine serum albumin (BSA) onto cellulose nanocrystals (CNCs). The –OH groups in HA and L-P bind with free H 2 O molecules, reducing the freezing point of the hydrogels to −35.7 °C, effectively solving the problem of low-temperature freezing. Meanwhile, the addition of CNCs@BSA enhances the maximum tensile stress of the P-HPCB hydrogels to 3.6 MPa and achieves a self-healing efficiency of 86.1%. The flexible sensors constructed with P-HPCB hydrogels can accurately detect and respond to human motion signals even at an extreme low temperature of −30.0 °C, demonstrating excellent sensitivity and stability. This provides insights for the application of hydrogel flexible sensors under severe cold conditions.