Microfluidic oscillators were tested by connecting pressure sensors (Model 142PC05D, Honeywell, NJ, USA) at the device inlets via Tygon tubing (Saint-GobainTM TygonTM R-3603 Clear Laboratory Tubing, Saint-Gobain Performance Plastics, Akron, OH, USA) to measure source pressure. Source pressure data was collected for both valves to quantify pressure buildup and release corresponding to fluid accumulation and evacuation, respectively, through the valves; our previous work highlighted the relationship between source pressure and drain pressure .
The occurrence of fluidic oscillations and the coincident timing of these oscillations relative to source pressure profiles were verified visually. All subsequent quantification and assessment, however, was performed using source pressure data. Data was obtained at a sampling rate of 1000 Hz, every 100 data points were averaged (resulting in 1 data point per 100 ms), and stored using LabVIEW (National Instruments, Austin, TX, USA).
Data was recorded for a minimum of four hours, of which the data acquired during the first hour for each condition was examined and discarded to ensure the volumetric flow and capacitance of the fluidic system had stabilized, and only the subsequent time (three hours) was assessed. Syringe pumps (Model KDS220, KD Scientific, Holliston, MA, USA and Model Fusion 200, Chemyx, Stafford, TX, USA) were used to provide constant volumetric flow to the device. One input, a 3 mL syringe (Syringe 1) remained connected to one inlet port for the entirety of the study, while the second (Syringe 2) was allowed to alternate between 3 mL, 10 mL, 30 mL and 60 mL plastic syringes (Becton, Dickinson and Company, Franklin Lakes, NJ, USA). The syringe pump was programmed with total volumetric inflow rates appropriate for each syringe pairing, such that Q2 ≥ Q1 and Q2 + Q1 = Qtotal. Voltage data were collected using LabVIEW and processed, in part, using the open-source peakdet .