Mechanically robust, flexible, conductive, and anti-freezing hydrogels reinforced by cellulose of wood skeleton.

Hydrogels are soft and wet materials, but their applications are always limited by insufficient mechanical strength and toughness, and they are prone to freezing at low temperatures. In this study, we introduced an eco-friendly approach to developing wood-based hydrogels reinforced by the naturally aligned wood skeleton (WS) through the Hofmeister effect. The resulting wood-based composite hydrogels exhibited a high tensile strength of 20 MPa and a strain of 35 % in the longitudinal direction. This impressive mechanical performance was primarily due to densely packed hydrogen bonding, physical entanglements, and van der Waals forces between the cellulose of WS, polyacrylamide (PAM), and poly(vinyl alcohol) (PVA) chains during polymerization. Notably, the polymerization was induced using wood carbon dots as initiators, imparting additional fluorescence features to the hydrogels. Afterward, by incorporating a metal salt (sodium chloride), the developed wood-based hydrogels maintained high conductivity (3.0 S/m) and mechanical properties even under low-temperature conditions (-20 °C). Moreover, the conductive hydrogels exhibited multifunctional sensing capabilities, including strain, temperature, and ultraviolet (UV) irradiation detection, making them highly suitable for applications in human motion monitoring and healthcare, particularly under harsh environmental conditions.