Aqueously Upcycled Lignin with Emergent Tribonegativity for Skin‐Integrated Triboelectronics

Valorizing lignin, a vast industrial byproduct and abundant biomass, is critical for a circular bioeconomy. However, the potential of lignin as a feedstock for functional polymers remains unrealized owing to poor aqueous solubility. Herein, a scalable aqueous process is reported that transforms lignin into printable electronic ink. The benign urea-based formulation increases lignin dispersibility by two orders of magnitude to 100 mg mL^-1, 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.