Nature-inspired dual self-catalytic system enabled by urushiol-iron: A green strategy toward tough, conductive, and anti-swelling hydrogels for wearable sensors.

Soft wearable electronics require hydrogels that are mechanically robust, electrically conductive, and easy to fabricate, yet these properties rarely coexist. Here, we solve this dilemma by taking inspiration from natural lacquer, a material used for millennia to create durable coatings. Its key component, urushiol, bears a unique molecular architecture with a catechol head for metal chelation and a long hydrophobic tail. We show that simply mixing urushiol with iron (III) ions (Fe3+) and ammonium persulfate at room temperature triggers rapid gelation through a dual self-catalytic mechanism. Unlike conventional Fenton chemistry, this pathway generates semiquinone radicals and an interpenetrating network reinforced by hydrogen bonding, metal coordination, and hydrophobic association. By optimizing the urushiol content, the resulting hydrogel achieves a tensile strength of 347 kPa, an elongation at break of 1158%, a skin-like modulus of ≈120 kPa, excellent anti-swelling properties, and a conductivity of 0.33 S·m-1. As a wearable sensor, it reliably detects human motions, enables a self-powered sensing platform, and even transmits Morse-coded distress signals underwater. This work elevates natural urushiol from an ancient coating material to a modern, green building block for smart bioelectronics.