3D-printing fabrication of microwave-microfluidic device for droplets network formation and characterisation

Microwave-microfluidic devices (MMDs) have emerged as precision tools for the rapid, accurate, sensitive, and non-invasive characterisation of low-volume liquids. However, the fabrication of MMDs remains a significant challenge due to the complexities associated with integrating fluidic ducts and electronic components. Herein, we present a versatile and economical 3D-printing approach for MMD fabrication, using liquid metal as an electrical conductor. Cyclic olefin copolymer, polylactic acid and polypropylene were identified as potential printable dielectric materials for MMD fabrication. 3D-printed cyclic olefin copolymer substrates exhibited the lowest loss tangent of 0.002 at 2.7GHz, making it an ideal material for high frequency engineering. Liquid metal, specifically gallium indium eutectic, was injected into the printed ducts to form conductive microwave structures. Exemplar MMDs were fabricated to integrate split-ring type microwave resonators and droplet-forming fluidic junctions. These devices were applied in the formation and characterisation of water-in-oil emulsions for constructing definable lipid-segregated droplet interface bilayer (DIB) networks. This work not only indicates the feasibility of using 3D-printing for rapid prototyping of customised MMDs but also demonstrates the potential of MMDs as a new research tool for biochemistry and synthetic biology.