Abstract
The ability to elicit distinct duty cycles from the same self-regulating microfluidic oscillator device would greatly enhance the versatility of this micro-machine as a tool, capable of recapitulating in vitro the diverse oscillatory processes that occur within natural systems. We report a novel approach to realize this using the coordinated modulation of input volumetric flow rate ratio and fluidic capacitance ratio. The demonstration uses a straightforward experimental system where fluid inflow to the oscillator is provided by two syringes (of symmetric or asymmetric cross-sectional area) mounted upon a single syringe pump applying pressure across both syringes at a constant linear velocity. This produces distinct volumetric outflow rates from each syringe that are proportional to the ratio between their cross-sectional areas. The difference in syringe cross-sectional area also leads to differences in fluidic capacitance; this underappreciated capacitive difference allows us to present a simplified expression to determine the microfluidic oscillators duty cycle as a function of cross-sectional area. Examination of multiple total volumetric inflows under asymmetric inflow rates yielded predictable and robust duty cycles ranging from 50% to 90%. A method for estimating the outflow duration for each inflow under applied flow rate ratios is provided to better facilitate the utilization of this system in experimental protocols requiring specific stimulation and rest intervals.
Highlights
IntroductionBiological and physiological systems are fundamentally regulated by oscillatory processes operating at discrete spatial and temporal scales
Emerging interest in microfluidic machines that directly utilize fluidic energy to execute core operations has prompted the development of self-regulated machines that, by virtue of their autonomous operation, have garnered much attention as potential platforms for basic biomedical research [1,2,3].Biological and physiological systems are fundamentally regulated by oscillatory processes operating at discrete spatial and temporal scales
The work presented here was motivated by the questions: how can a single microfluidic oscillator circuit be designed to best support multiple stimulatory frequencies and rest periods; and how can this be done in a manner that is easy to understand and perform by non-microfluidic experts? We have previously demonstrated the ability to alter oscillation frequency by modifying flow rate, and to alter duty cycle by modifying the device itself [1,2]
Summary
Biological and physiological systems are fundamentally regulated by oscillatory processes operating at discrete spatial and temporal scales. Our understanding of these systems, has benefited from the development of pulsatile stimulation techniques capable of manipulating the temporal dynamics of these processes and investigating the role of timing within them. The control systems underlying their operation, have typically remained external from the fluidic devices themselves [12,13,14] An awareness that this rise in peripheral equipment cost may limit “next-generation” microfluidic systems has motivated the development of autonomous, pre-programmed, fluidic systems [1,12,13,14,15,16,17]. Foremost among these is the microfluidic oscillator [18]
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