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Microfluidic swap structure to enhance on-chip liquid mixing

A method to swap the position of two parallel laminar flowing liquids in a microchannel is presented. To attain the swap, a three-dimensional fluidic channel structure was realized within the microchannel by two-photon polymerization. The swap structure consists of four neighboring channels that divide the laminar flow in four equal portions. The outer two channels (channels #1 and #4) just go straight forward, but the middle channels (channels #2 and #3) are curved in such a way that the two liquids swapped position at the outlet of the structure. To fabricate the device we employ standard microtechnology fabrication methods that can be combined with state-of-the-art two-photon polymerization to create three-dimensional microstructures within the microchannel. The microfluidic channel is 90 μm wide and 50 μm high, the four channels of the swap-structure have a minimal internal width of 18 μm and height of 14 μm. First experiments confirm the swap-function of the device. The principle of swapping can pave the way to more efficient passive micromixing elements.