Durable skin-integrated liquid metal-based conductive tattoo for imperceptible and untethered human machine interfaces

Abstract

Electronic tattoos (e-tattoos) hold great potential for next-generation wearable electronics, but their widespread adoption is limited by challenges in electrical conductivity, mechanical durability, and user comfort. In this study, we introduce an Conductive and Durable EGaIn Particle (CDP) ink designed for imperceptible, untethered, and on-palm skin-integrated e-tattoos to overcome these limitations. By leveraging hydrogen bonding between poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) (PVB-A) with nanosized silver (Ag) particles and oxide shell of EGaIn-based liquid metal particles, CDP achieves an exceptional initial electrical conductivity of 1.35 × 10⁵ S m⁻¹ without post-activation. This formulation facilitates the formation of a stable conductive percolating network while maintaining outstanding mechanical durability and resilience under repeated mechanical stresses, such as rubbing and pinching. These properties arise from the ink’s high conductivity even at a low Ag content and the intrinsic robustness of PVB-A with a high density of hydroxyl groups. To demonstrate its functionality, a CDP-based e-tattoo was applied to a human palm as a pressure-sensitive interconnect for human–machine interfaces. This system wirelessly transmitted real-time pressure data from human fingers to a robotic hand, enabling precise grip control. Our findings highlight the potential of CDP ink for advanced, highly durable e-tattoos in interactive and wearable electronic applications.