Mussel-inspired cellulose nanofiber/poly(vinyl alcohol) hydrogels with robustness, self-adhesion and antimicrobial activity for strain sensors

Flexible strain sensors have attracted substantial attention given their application in human-computer interaction and personal health monitoring. Due to the inherent disadvantages of conventional hydrogels, the manufacture of hydrogel strain sensors with high tensile strength, excellent adhesion, self-healing and antimicrobial properties in vitro, and conductive stability is still a challenge. Herein, a conductive hydrogel consisting of polydopamine-coated cellulose nanofibers (CNF@PDA), carbon nanotubes (CNT), and polyvinyl alcohol (PVA) was developed. The CNTs in PVA/CNF@PDA/CNT hydrogels were uniformly dispersed in the presence of CNF@PDA by hydrogen bonding, resulting in a nearly threefold increase in conductivity (0.4 S/m) over hydrogels without PDA. The hydrogel exhibited satisfactory tensile properties (tensile stress up to 0.79 MPa), good fatigue resistance, self-recovery and excellent antimicrobial activity in vitro. It showed excellent adhesion, especially the adhesion strength of pigskin was increased to 27 kPa. In addition, the hydrogel was used as a strain sensor, exhibiting excellent strain sensitivity (strain coefficient = 2.29), fast response (150 ms), and great durability (over 1000 cycles). The fabricated strain sensors can detect both large and subtle human movements (e.g., wrist bending and vocalization) with stable and repeatable electrical signals, indicating potential applications in personal health monitoring.