This paper describes a method to construct microfluidic pathways without physical walls—wall-less microchannels. Compared to the previous wall-less microfluidics based on two-dimensional patterns, this method uses three-dimensional ring arrays and two immiscible liquids. The distant rings generate free-standing liquid pathways in order to minimize liquid surfaces contacted to solid walls. In the experimental study, we reduced the liquid-solid interface area per volume to 17.3% of that of the conventional microchannels with squared cross-sections. We envision that this aspect would be significant in micro/nano-fluidics, whose surface-area-to-volume ratio is extremely large.

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See supplementary material at http://dx.doi.org/10.1063/1.4752720 for ring dimensions, the estimation of the interface-area-to-volume ratios in the microchannels, SEM photographs of the fabricated ring arrays, and liquid pathways visualized by confocal microscopy.

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