Lignin-Containing Cellulose Nanofibers Enhanced PVA/MXene Hydrogels: Combining Toughness and Conductivity for Durably Wearable Sensing

Conductive hydrogels (CHs) are promising for flexible electronics in artificial intelligence and digital healthcare, but they still lack mechanical durability and long-term stability. Here, sustainable lignin-containing cellulose nanofibers (LCNFs) were used to strengthen the poly(vinyl alcohol) (PVA)/transition metal carbide and nitride (MXene) hydrogels through a simple “one-pot” procedure (abbreviated as P(LxMy)z). Owing to the rigid and polar phenolic hydroxyl groups on lignin, LCNFs formed dense hydrogen bonding with both PVA and MXene, dissipated the external stress, and endowed the composite hydrogels with superior mechanical properties (a tensile strength of ∼1.55 MPa and a toughness of ∼2.85 MJ m–3), conductivity (∼0.13 S m–1), stability, and biocompatibility. Combining all these features, the P(LxMy)z hydrogels demonstrated a sensitive (GF value of ∼2.3) and durable (more than 2400 cycles) response to deformation, which can be applied as an epidermal sensor to detect both drastic (e.g., joint movement) and subtle (e.g., swallow and frown) human motions and even to detect information on different speeches and handwritings. Thus, this work paves a new way to build tough, stable, and biocompatible CHs, demonstrating significant potential for durable and precise epidermal sensing applications.