Aqueously Upcycled Lignin with Emergent Tribonegativity for Skin‐Integrated Triboelectronics

, while preserving its molecular integrity by retaining 97.6% of its fragile β-O-4' ether linkages. This process enables the thermodynamically driven self-assembly of lignin polymers during printing to create a functional, nanotextured surface with emergent tribonegativity, without the use of harsh solvents or lithography. As a proof of concept, skin-integrated triboelectric sensors fabricated from this ink generate high-fidelity signals sufficient for objectively classifying human mental workload, with a performance comparable to gold-standard electrocardiography. This study establishes a generalizable strategy for creating high-performance, sustainable electronics from waste biomass.