3D‐Printed Multi‐scale Fluidics for Liquid Metals

Abstract Room‐temperature eutectic Gallium Indium (eGaIn)‐based devices offer stretchable, conductive, and reconfigurable properties for robotics, communications, and medicine. Microfluidics enables eGaIn device creation, but these typically have larger feature sizes. Recent three‐dimensional (3D) printing advancements, particularly direct laser writing (DLW), allow for sub‐100 µm microfluidic devices. However, interfacing DLW microfluidics with larger systems poses challenges in channel resist removal, eGaIn filling, and electrical integration, limiting micro‐scale liquid metal device application. This study introduces a multiscale, cost‐effective, three‐step process combining DLW‐fluidic microchannels with centimeter‐scale substrates made via stereolithography (SLA). It establishes a robust interface between independently printed materials and simplifies eGaIn filling in microfluidic channels as small as 50 µm, potentially enabling smaller liquid metal features. The research also presents eGaIn coils with 43–770 mΩ resistance and 2–4 nH inductance. This process facilitates low‐temperature, conductive, flexible interfaces for sensors, actuators, and circuits, and expands the range for size‐dependent properties of passive electronic components like resistors, capacitors, and inductors from liquid metal.