Design of Cellulose Nanocrystal-Based Self-Healing Nanocomposite Hydrogels and Application in Motion Sensing and Sweat Detection

Hydrogels, as flexible materials, have been widely used in the field of flexible sensors. Human sweat contains a variety of biomarkers that can reflect the physiological state of the human body. Therefore, it is of great practical significance and application value to realize the detection of sweat composition and combine it with human motion sensing through a hydrogel. Based on mussel-inspired chemistry, polydopamine (PDA) and gold nanoparticles (AuNPs) were coated on the surface of cellulose nanocrystals (CNCs) to obtain CNC-based nanocomposites (CNCs@PDA-Au), which could simultaneously enhance the mechanical, electrochemical, and self-healing properties of hydrogels. The CNCs@PDA-Au was composited with poly(vinyl alcohol) (PVA) hydrogel to obtain the nanocomposite hydrogel (PVA/CNCs@PDA-Au) by freeze-thaw cycles. The PVA/CNCs@PDA-Au has excellent mechanical strength (7.2 MPa) and self-healing properties (88.3%). The motion sensors designed with PVA/CNCs@PDA-Au exhibited a fast response time (122.9 ms), wide strain sensing range (0-600.0%), excellent stability, and fatigue resistance. With the unique electrochemical redox properties of uric acid, the designed hydrogel sensor successfully realized the detection of uric acid in sweat with a wide detection range (1.0-100.0 μmol/L) and low detection limit (0.42 μmol/L). In this study, the dual detection of human motion and uric acid in sweat was successfully realized by the designed PVA/CNCs@PDA-Au nanocomposite hydrogel.