3D-Printed Autonomous Capillaric Circuits

Capillaric circuits (CCs) are advanced capillary microfluidic devices that move liquids in complex pre-programmed sequences without external pumps and valves-relying instead on microfluidic control elements powered by capillary forces. CCs were thought to require high-precision micro-scale features manufactured by photolithography in a cleanroom, which is slow and expensive. Here we present rapidly and inexpensively 3D-printed autonomous CCs. Molds for CCs were fabricated with a benchtop 3D-printer, Poly(dimethylsiloxane) replicas were made, and fluidic functionality was verified with aqueous solutions. We established design rules for 3D-printed CCs by a combination of modelling and experimentation. The functionality and reliability of 3D-printed trigger valves-an essential fluidic element that stops one liquid until flow is triggered by a second liquid-was tested for different geometries and different solutions. Trigger valves with geometries up to 80-fold larger than cleanroom-fabricated ones were found to function reliably. We designed 3D-printed retention burst valves that encode sequential liquid drainage and delivery using capillary pressure differences encoded by varying valve height and width. Using an electrical circuit analogue of the CC, we established circuit design rules for ensuring strictly sequential liquid delivery. We realized a 3D-printed CC with reservoir volumes 60 times larger than cleanroom-fabricated circuits and autonomously delivered eight liquids in a pre-determined sequence in < 7 min, exceeding the number of sequentially-encoded, self-regulated fluidic delivery events apreviously reported. Taken together, our results demonstrate that 3D-printing enables rapid prototyping of reliable CCs with improved functionality and potential applications in diagnostics, research and education.