Nanocellulose-Reinforced Conductive Hydrogels With High Stretchability and Sensitivity, Temperature, and pH Multi-Responsive Properties for Flexible Wearable Sensor Devices

Conductive hydrogels have emerged as promising candidates for flexible sensing devices, yet their widespread application is hindered by the challenge of simultaneously achieving mechanical stability and multi-parameter responsiveness. To address this issue, we developed a dual cross-linking strategy combining physical and chemical interactions, and reinforced with cellulose nanofibrils (CNF). By employing CNF as a structural scaffold, we copolymerized thermoresponsive N -isopropylacrylamide (NIPAM) with acrylamide (AM) to construct a mechanically robust three-dimensional network. This architecture not only enhanced the mechanical properties of the hydrogel but also endowed it with dual pH- and temperature-responsive behavior. Furthermore, the incorporation of Al 3+ ions facilitated strong coordination and electrostatic interactions with the polymer matrix, significantly improving conductivity and structural stability. The resulting P(AM-co-NIPAM)/CNF/AlCl 3 hydrogel exhibited tunable solubility across a broad pH range (2–14) and temperature spectrum (10°C–50°C), demonstrating exceptional environmental responsiveness (swelling ratio reached 499 at a pH of 2 and 1632 at a pH of 14). Moreover, the hydrogel possessed outstanding mechanical performance, with an elongation at break of 488% and a tensile strength of 0.1008 MPa. When applied as a strain sensor, the hydrogel exhibited a wide sensing range (300% strain), rapid responsed time (600 ms), and high sensitivity, enabling the detection of complex human motions and spatial variations. This work presents a versatile approach for designing multifunctional conductive hydrogels with potential applications in flexible electronics and wearable sensors.