In microfluidic design considerations, there are engineering and manufacturing challenges that impact the ability to go from concept to a functional device with the expected performance. In some microfluidic designs, the geometry of the channel, the sharpness of features, and the materials and method of manufacture all impact the device performance.

This is particularly true for generating droplets that are less than 100 microns in diameter, where the size and sharpness of the nozzle is important for consistent droplet sizes. For acoustic microfluidics, the sharpness of corner features enhances the acoustic forces that create fluid flow and separations in the device.

However, there are many applications for which the geometry of the channels is not important for the performance of the device, but provides a means for transporting and combining fluids to execute a workflow. An example of this would be the execution of a standard sandwich immuno assay where sample, detection antibodies, washes and readout reagents are combined, mixed, and delivered sequentially to a detection region where a capture antibody is bound to a surface.

One could think of these two different design regimes in microfluidics as the very small features that are critical for function being similar to microprocessors in an integrated circuit, while the latter, which involves toggling fluids around in a circuit, and is more akin to printed circuit boards that often support the function of integrated circuits. In fact, the equations used to describe pressure drops in fluid circuits are parallel to the resistance in electronic circuit boards. (historically, however, the development of the concepts and equations for electrons moving in bulk copper traces was borrowed from fluid dynamics…we have come full circle!)

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