Flexible Electrodes are Fabricated Using 3D Printed Liquid Metal Composite Ink for ECG and EEG Signal Monitoring

Smart wearable electronics are gaining increasing attention for use in human–machine interfaces, health monitoring, and motion tracking. However, fabricating conventional flexible electronics typically involves complex processes. Here, we demonstrate that 3D printing can be employed to fabricate high-precision, highly sensitive flexible electrodes. We developed three types of liquid metal-based composite inks. Using 3D printing, we deposited liquid metal hybrid inks onto flexible, high-viscosity double-sided polyethylene or PET substrates, producing skin-adhesive sensors for physiological monitoring. With LM composite inks, we fabricated customized electrocardiogram (ECG) and electroencephalogram (EEG) electrodes using software. These were printed on 300 µm thick polyethylene substrates at a print speed of 4% and a nozzle-to-substrate distance of 500 µm. The resulting three-layer ECG/EEG electrodes are flexible, skin-adhesive, and have a total thickness of 910 µm, with sizes of 8.2 × 5.9 cm and 5.0 × 4.6 cm, respectively. After encapsulation with epoxy resin, the electrodes achieved a conductivity of 1.63 × 10⁶ S·m⁻¹. They show potential for early disease detection by accurately distinguishing between EEG signals in states such as excitement and sleep. The printed circuits are precise, visually well-defined, and suitable for reliable heart rate and physical activity monitoring directly on the skin.