3D-printed microfluidic-microwave device for droplet network formation and characterisation

Microfluidic-microwave devices (MMDs) have emerged as precision tools for the rapid, accurate, sensitive, and non-invasive characterisation of liquids in low-volumes. However, the fabrication of MMDs remains a significant challenge. This is due to the complexities associated with integrating fluidic ducts and electronic components. Herein, we present a versatile and economical 3D-printing approach using ducts filled with liquid metal as an electrical conductor. Cyclic olefin copolymer, polylactic acid, and polypropylene were identified as potential printable dielectric materials for MMD fabrication. Substrates of 3D-printed cyclic olefin copolymer exhibited the lowest loss tangent (0.002 at 2.7GHz), making them suitable materials for high-frequency microwave devices. Liquid metal, specifically gallium indium eutectic, was injected into the printed ducts to form conductive microwave structures. Exemplar MMDs operating at 2GHz integrated split-ring microwave resonators and droplet-forming fluidic junctions. These devices were used in the formation and characterisation of water-in-oil emulsions, constructing definable lipid-segregated droplet interface bilayer (DIB) networks. This work indicates the feasibility of using 3D-printing manifolds for the rapid prototyping of customized MMDs, and also demonstrates the potential of MMDs as a new analytical research tool in microfluidic based biochemistry and synthetic biology.