Inertial focusing and filtration of microparticles with expansion-contraction structures in microchannel

In this study, we proposed a simple microfluidic device with expansion-contraction structures to obtain a single focusing and filtration of microparticles in different sizes. The presented device comprised of three different regions, the straight rectangular pre-focusing channel, the second focusing channel with expansion-contraction structures, called notches, and the observing region. The randomly distributed microparticles align to the two-equilibrium position in the first region with the assistance of inertial lift forces. In the second region, the uneven structures induce the dean drag force in the microchannel. The inertial lift forces in combination with the dean drag force let the microparticles all align to one equilibrium position gradually. We investigated different geometry of notches with the different length ratios (L/C) to analysis the focusing efficiency and the filtration efficiency of microparticles with different sizes. The highest focusing efficiency of microparticles with 6 and 12 mu m diameter are 94 and 99% respectively in the presented device. The filtration efficiency of microparticles with 12 mu m diameter exceeds 99% from the mixture of 1 and 12 mu m microparticles. With small L/C value, the dean flow strength is higher in the entire expansion region, and the smaller microparticles are relatively easy to follow the high strength dean flow which caused dramatically decrease in focusing efficiency. The notch height also affects the focusing efficiency even with the same L/C value. The optimized notch height with highest focusing efficiency is positive related to the microparticles size. In this study, we found the design rule of the expansion-contraction structures in microchannel. This device has the ability to focus and filter the specific size of microparticles from the mixture of microparticles with different sizes effectively, which benefits the performance of flow cytometry and other biomedical applications.

Automated summary

In this study, a microfluidic device with expansion-contraction structures was proposed to achieve single focusing and filtration of microparticles in different sizes. The device showed high focusing efficiency and filtration efficiency, and was able to focus and filter specific size microparticles from mixtures effectively.