Using printing orientation for tuning fluidic behavior in microfluidic chips made by fused deposition modeling 3D printing

Fluidic behavior in microfluidic devices is dictated by low Reynolds numbers, complicating mixing. Here, the effect of the orientation of the extruded filament on the fluidic behavior is investigated in fused deposition modeling (FDM) printed fluidic devices. Devices were printed with filament orientations at 0°, 30°, 60°, and 90° to the direction of the flow. The extent of mixing was observed when pumping yellow and blue solutions into the inlets of a Y-shaped device, and measuring the extent of mixing of two colored solutions under different angles and at flow rates of 25, 50, and 100 μL/min. Fluidic devices printed with filament extruded at 60° to the flow showed the highest mixing efficiency, but results obtained at 30° suggested more complex fluid movement, as the measured degree of mixing decreased along the fluidic channel at higher flow rates. To explore this, a device with -37° filament orientation on the top surface was designed to align with the direction of the first fluid input channel and +37° on the bottom surface of the channel to align with the direction of the second fluidic input. Results indicated a rotational movement of the fluids down the microchannel, which were confirmed by computational fluid dynamics. These results demonstrate the impact of the filament extrusion direction on fluidic behavior in microfluidic devices made by FDM printing. Two chips with laminar flow (0° filament direction) or mixing flow (+37/-37° filament direction) were used to perform isotachophoresis and colorimetric detection of iron in river water, respectively, demonstrating the simplicity with which the same device can be tuned for different applications simply by controlling the way the device is printed.