Laser Direct-Write Manufacturing of Conductive Hydrogel Sensors: A Conductive Interface Pre-programming Strategy

Abstract

Conductive hydrogel sensors hold great promise for flexible electronics but face an inherent trade-off between sensitivity and mechanical stability. Here, we propose a laser pre-structuring strategy and elevate it as a conductive interface pre-programming methodology. Microgrooves are first created on the hydrogel surface by laser direct writing, followed by in situ deposition of a silver conductive layer via two-step chemical reduction. The fabrication process uses dimethyl sulfoxide as a processing aid, which is completely removed by subsequent solvent exchange, yielding a final hydrogel with no residual organic solvent. The mild solution-based conditions and the use of lignosulfonate, a renewable industrial byproduct, contribute to the overall sustainability of the manufacturing route. The laser pre-structuring not only modifies the topography but also actively induces subsequent silver metallization, resulting in significant spatially selective thickening within the grooves. Through this pre-programming design, three key elements, namely stress concentration, silver layer thickness gradient, and crack evolution path, are spatially coupled within the same predefined region. Upon stretching, the groove geometry provides stress concentration; the locally thickened silver layer is more prone to brittle fracture, and the in situ reduction ensures strong interfacial bonding. These three elements work synergistically, transforming random crack behavior into an ordered, spatially predefined controllable crack amplification process, terming the structure-thickness synergistic sensitization mechanism. The optimized sensor exhibits a 147% relative increase in gauge factor, while the tensile strength and elongation at break of the hydrogel matrix remain unchanged. The integrated sensor demonstrates excellent linearity over 0–0.5 N and achieves >99% monitoring accuracy. Comparative robotic gripper experiments show that pre-structuring amplifies the relative resistance change by several times to an order of magnitude. In summary, the proposed conductive interface pre-programming strategy provides a physical design paradigm for decoupling sensitivity and mechanical stability in flexible sensors.