Top-down approach making anisotropic, stable and flexible wood-based ionogels for wearable sensors

Ionogels exhibit outstanding ionic conductivity, thermal stability, and non-volatility, positioning them as highly promising for sensor devices rivaling hydrogels. However, the inherent limitation of most existing ionogels is that their strength and toughness are not ideal, which significantly hinders their widespread application. One possible method is using natural wood with anisotropic properties to reinforce ionogels. Herein, we reported a top-down approach to obtain a semi-dissolved wood template, in which the delignified balsa wood was heated and impregnated in an ionic liquid to partially dissolve the cellulose in the wood skeleton. Finally, acrylic acid was infiltrated into the wood template, and the wood-based ionogels with a dual network were successfully synthesized by in-situ polymerization. The prepared wood-based ionogels were significantly anisotropic with longitudinal strength up to 9.0 MPa and radial strength of 0.97 MPa. These wood ionogels also have translucency (53.9 %), anti-drying (remain stable at room temperature for more than 30 days), fatigue resistance (>500 loading cycles), and flexibility. In addition, they have excellent electrical conductivity (3.8 μS cm−1) with high sensitivity (GF = 8.6), making them ideal candidates for strain sensors capable of detecting a wide range of human activities. The preparation of gel using semi-dissolved wood as a template provides an advanced strategy for producing biomass-based flexible gel materials.