Open Access Publications from the University of California

## Microfluidic Circuitry via Additive Manufacturing

• Author(s): Glick, Casey Carter
The basic theory of microfluidic control systems, including the hydraulic analogy and fluidic circuitry, the low Reynolds number approximation to the Navier-Stokes equations, and neglectable terms in microfluidic models are first investigated. Optofluidic lithography, where photocurable liquids are selectively solidified under UV exposure, is utilized as a means of fabricating moving microfluidic structures within a microchannel. Several variants of microfluidic control mechanisms are demonstrated, including current sources (for regulation of fluid flow-rates to $29.2 \pm 0.8$ \si{\micro\liter/min} for pressures from $5-10$ kPa), and microfluidic gain valves (for controlling a high-pressure channel with a low-pressure one to achieve a dynamic gain of $6.30 \pm 0.23$).
By using the multi-jet-based additive manufacturing, fully-3D-printed microfluidic circuitry components are demonstrated, including fluidic resistors, capacitors, diodes (for a diodicity of $80.6 \pm 1.8$), and transistors (for a dynamic pressure gain of $3.01 \pm 0.78$) through the combination of experimental, simulation, and analytical methods, which are integrated complex microfluidic circuits, such as half- and full-wave microfluidic rectifiers. The hydraulic analogy circuitry exhibits similar transfer functions to its electronic counterparts, but ultimately behaves more similarly to vacuum triodes than to actual transistors. When combined with fully-realized microfluidic IF-gate and CMOS-analog components, this research may allow for fabrication of analog microfluidic operational-amplifiers, which could allow for fully-analog control of microfluidic systems using high-gain amplification of small pressure signals, and the CAD-based nature of the design process makes it simple for researchers to readily combine multiple microfluidic components into larger integrated microfluidic circuit networks.