On-chip mixing of liquids with swap structures written by two-photon polymerization

Abstract

A fluidic micromixer realized by two-photon polymerization writing is embedded in a predefined microchannel. The micromixer consists of a 3D defined channel system which swaps incoming fluid streams, resulting in laminar alternating streams consisting of the two liquids to be mixed. Due to the shortened diffusion length, mixing times are reduced dramatically to 50 ms or lower. The structure is designed in such a way that the fluidic resistance in each swapper channel is balanced, yielding equal distribution of the alternating streams. The mixer element has a total size of about $225\times 100\times 50\,\upmu \hbox {m}^{3}$, fitting exactly in a prefabricated microchannel. The structure is strongly anchored in the channel so that it can handle high flow rates of up to 100 $\upmu \text {L/min}$ (corresponding to an average flow velocity of $400\,\text {mm/s}$). A benefit of the fabrication method is the short processing time. The writing of one mixer element takes less than $30\,\text {s}$, so that a whole wafer can be processed in typically less than one hour.