Proanthocyanidin-enhanced wettability and adhesion in liquid metal inks for multi-substrate patterning in soft electronics

The remarkable potential of gallium-based liquid metals has been extensively demonstrated in the field of wearable health-managing devices due to their unparalleled conductivity, flowability, and biocompatibility. However, the high surface tension and poor interfacial adhesion of liquid metals pose great challenges for their intricate patterning on flexible substrates. To address these issues, this study develops a liquid metal ink with greatly enhanced wettability and adhesion that utilizes natural polyphenol oligomeric proanthocyanidins (OPCs) as surface functional agents to modify EGaIn nanoparticles. Via precise optimization of rheology and wettability, prepared OPC/EGaIn NPs inks can be directly written on different substrates with various surface energies and maintain stable electrical performance under large-scale deformation. When patterned on elastic fibrous membranes as super-conformal and flexible epidermal bioelectrodes, the composite inks featuring low on-skin impedance can reliably and accurately monitor electrocardiogram (ECG) signals over long periods and stably detect surface electromyography (sEMG) signals of different sports activities. This research provides a novel solution for the patterned fabrication of liquid-metal-based soft electronics and the advancement of wearable technology for electrophysiological monitoring.