A millisecond passive micromixer with low flow rate, low sample consumption and easy fabrication

Fast mixing of small volumes of solutions in microfluidic devices is essential for an accurate control and observation of the dynamics of a reaction in biological or chemical studies. It is often, however, a challenging task, as the Reynolds number (Re) in microscopic devices is typically < 100. In this report, we detail a novel mixer based on the staggered herring bone (SHB) pattern and split-recombination strategies with an optimized geometry, the periodic rotation of the flow structure can be controlled and recombined in a way that the vortices and phase shifts of the flow induce intertwined lamellar structures, thus increasing the contact surface and enhancing mixing. The optimization improves the mixing while using a low flow rate, hence a small volume for mixing and moderate pressure drops. The performances of the patterns were first simulated using COMSOL Multiphysics under different operating conditions. The simulation indicates that at very low flow rate (1-12 mu L center dot min(-1)) and Re (3.3-40), as well as a very small working volume (similar to 3 nL), a very good mixing (similar to 98%) can be achieved in the ms time range (4.5-78 ms). The most promising design was then visualized experimentally, showing results that are consistent with the outcomes of the simulations. Importantly, the devices were fabricated using a classical soft-lithography method, as opposed to additive manufacturing often used to generate complex mixing structures. This new device minimizes the sample consumption and could therefore be applied for studies using precious samples.

Automated summary

This study presents a novel microfluidic mixer based on the staggered herring bone pattern and split-recombination strategies, which improves mixing efficiency and reduces sample consumption. The optimized geometry allows for controlled flow structure rotation and increased contact surface, leading to enhanced mixing effects. The device, fabricated using soft-lithography, demonstrates good mixing performance under low flow rate and small working volume conditions, making it suitable for studies with precious samples.