Electrohydrodynamic Printing of Liquid Metal Composites for Breathable Interfaces in Recyclable Thermoelectric Wearables.

Thermal interfaces for wearable thermoelectric generators must efficiently transfer heat from the skin while remaining comfortable, yet conventional materials sacrifice breathability for higher thermal conductivity. Here, we develop a breathable thermal interface using electrohydrodynamic printing of liquid metal (LM)-boron nitride (BN)-thermoplastic polyurethane (TPU) composites. The resulting microscale lattice creates localized contact points with the skin, enabling air and moisture transport while maintaining continuous thermal pathways. The composite incorporates thermally conductive, electrically insulating fillers, yielding a through-plane thermal conductivity of 0.37 W·m-1·K-1. When integrated into wearable thermoelectric generators, the printed interface acts as both a compliant thermal interface and a patterned heatsink, supporting heat transfer while preserving skin compatibility. Guided by multiphysics modeling, the device generates a power density of 0.43 μW·cm-2 at thermal equilibrium from an initial temperature difference of 10 °C. The device can be disassembled to recover and reuse both composite constituents and thermoelectric elements without measurable performance loss. This work highlights an interface design approach that prioritizes breathability and skin compatibility in flexible thermoelectric devices, with further improvements in power output and mechanical robustness needed for practical deployment.