Thickness-Gradient Liquid Metal Connectors for Seamless Electrophysiological Sensors.

High-fidelity electrophysiological monitoring requires wearable bioelectronic devices with mechanical properties closely matched to human skin. However, current approaches focus primarily on electrode design and performance, while overlooking mechanical compliance and interfacial continuity with complex and dynamic human skin. Mechanical mismatches across electrodes, connectors, and interconnects often lead to interfacial noise, motion artifacts, and electrical instability. In order to overcome these critical issues, we introduce a thickness-gradient liquid metal (LM)/SEBS connector that enables seamless interfacial integration with skin, electrode, and interconnector interfaces through gradual mechanical compliance matching and manually activated metal network formation. The activated LM forms continuous and robust conductive networks, maintaining electrical stability under large tensile strain (∼1100%) and for repeatable deformation cycles. Skin-mimetic conformal integration suggested here suppresses interfacial void formation and stress concentration and thereby preserves stable electrical pathways under dynamic skin deformation. As a result, the proposed system delivers markedly improved signal amplitude and signal-to-noise ratio, along with substantially lower noise, relative to conventional connector platforms. By systematically aligning mechanical compliance across sensor components, this mechanically adaptive design preserves seamless electrical pathways and minimizes motion-induced artifacts under dynamic conditions, providing a robust platform for reliable electrophysiological monitoring in long-lasting wearable bioelectronics.