Pneumatic oscillator circuits for timing and control of integrated microfluidics

Significance Lab-on-a-chip devices aim to miniaturize laboratory procedures on microfluidic chips, which contain liquid circuits instead of electronics. Although the chips themselves are small, they are typically dependent on off-chip control machinery that negates their size advantage. If a computer controller could be built out of microfluidic valves and channels, it could be integrated to create a complete system-on-a-chip. We engineer a critical component for such a computer: a microfluidic clock oscillator with suitable timing accuracy to control diagnostic assays. Further, we leverage this oscillator to build a self-driving pump for on-chip liquid transport. Thus, we demonstrate two critical components for building self-contained lab-on-a-chip devices. Frequency references are fundamental to most digital systems, providing the basis for process synchronization, timing of outputs, and waveform synthesis. Recently, there has been growing interest in digital logic systems that are constructed out of microfluidics rather than electronics, as a possible means toward fully integrated laboratory-on-a-chip systems that do not require any external control apparatus. However, the full realization of this goal has not been possible due to the lack of on-chip frequency references, thus requiring timing signals to be provided from off-chip. Although microfluidic oscillators have been demonstrated, there have been no reported efforts to characterize, model, or optimize timing accuracy, which is the fundamental metric of a clock. Here, we report pneumatic ring oscillator circuits built from microfluidic valves and channels. Further, we present a compressible-flow analysis that differs fundamentally from conventional circuit theory, and we show the utility of this physically based model for the optimization of oscillator stability. Finally, we leverage microfluidic clocks to demonstrate circuits for the generation of phase-shifted waveforms, self-driving peristaltic pumps, and frequency division. Thus, pneumatic oscillators can serve as on-chip frequency references for microfluidic digital logic circuits. On-chip clocks and pumps both constitute critical building blocks on the path toward achieving autonomous laboratory-on-a-chip devices.