ABSTRACT

Micromixers have been a critical component in microfluidic platforms. However, most 2-D passive micromixers produce optimal mixing at a high flow rate range, while 3-D structures require mm-scale channels or complex assembly unsuitable for microfluidic applications. Here, we report a 3-D PDMS micromixer based on the splitting-stretching-recombination of streams to enhance diffusion, which can rapidly and effectively mix solutions with low Reynolds numbers (0.01 ~ 10). The fabrication requires only two steps, including two-photon polymerization (2PP) 3D printing and soft lithography, which provide high resolution, reproducibility, and integrability. We investigated the mixing behavior of the micromixer by CFD simulations and experimental characterization by a confocal microscope, and the results consistently confirmed better performance and miniaturization than previous PDMS micromixers. It achieved a mixing efficiency higher than 0.9 (complete mixing status) for solutions with flow rates under 60 μL/min within a volume of 20.5 nL. We also found that the device showed little degradation (<1.5%) in mixing performance for fluids with increased viscosity (up to ~50 times that of pure water) and was able to mix large particles such as fluorescent proteins and microbeads rapidly and efficiently for biomedical applications. This simple, stable, and efficient micromixer demonstrates excellent potential in accurate control and dynamics investigation of biological and chemical reactions in integrated microfluidic platforms.