Polydopamine-coated cellulose nanofibers reinforced multifunctional conductive hydrogels for flexible strain sensors

Flexible hydrogel-based sensors have attracted considerable attention for applications in human motion monitoring, health management, electronic skin, and human-machine interaction. However, it remains challenging to develop hydrogel-based strain sensors that simultaneously possess good mechanical properties, self-adhesion, self-healing capability, and antibacterial activity. Herein, polydopamine-coated cellulose nanofibers (CNF@PDA) and polyaniline (PANI) were incorporated into a polyacrylamide (PAM) network to fabricate a multifunctional CNF@PDA/PANI_(x)/PAM (CPP_xP) hydrogel. The introduction of CNF@PDA not only enhances the mechanical strength and adhesion of the hydrogel, but also improves the dispersion stability of PANI, thereby contributing to enhanced conductivity and sensing stability. As a result, the obtained hydrogel exhibits a tensile strength of 0.073 MPa, an elongation at break of 859.3%, excellent self-healing capability, an adhesion strength of 42.73 kPa on porcine skin, and good antibacterial activity. Importantly, the hydrogel can be used as a strain sensor with high sensitivity (GF = 7.95), a rapid response of 120 ms, and excellent durability over 500 cycles. The sensor is capable of monitoring both subtle and large human motions, highlighting its great potential for applications in flexible wearable devices and intelligent sensing systems.