Hydrodynamic microfluidic platforms have been proven to be useful and versatile for precisely sorting particles/cells based on their physicochemical properties. In this study, we demonstrate that a simple lattice-shaped microfluidic pattern can work as a virtual sieve for size-dependent continuous particle sorting. The lattice is composed of two types of microchannels ("main channels" and "separation channels"). These channels cross each other in a perpendicular fashion, and are slanted against the macroscopic flow direction. The difference in the densities of these channels generates an asymmetric flow distribution at each intersection. Smaller particles flow along the streamline, whereas larger particles are filtered and gradually separated from the stream, resulting in continuous particle sorting. We successfully sorted microparticles based on size with high accuracy, and clearly showed that geometric parameters, including the channel density and the slant angle, critically affect the sorting behaviors of particles. Leukocyte sorting and monocyte purification directly from diluted blood samples have been demonstrated as biomedical applications. The presented system for particle/cell sorting would become a simple but versatile unit operation in microfluidic apparatus for chemical/biological experiments and manipulations.

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Here we describe a continuous particle/cell sorting system using asymmetrically patterned, lattice-shaped microchannel array structures. The microchannel is composed of two types of microchannels, which are placed in a lattice pattern at a right angle. There is a difference between the densities of these two types of microchannels, which generates the asymmetric flow distribution at every intersection. Large particles/cells are separated from the streamline, resulting in the continuous size-dependent cell sorting. We fabricated PDMS microfluidic devices, and successfully sorted micrometer-sized particles based on size with high separation accuracy. It was clearly shown that the separation size of particles/cells was dominated by the microchannel geometries including the densities of the microchannels and the slanted angles.As an application for cell sorting, we demonstrated the blood cell separation from a diluted blood sample. Erythrocytes and leucocytes were accurately separated and the ratio of recovered leucocytes was raised to ~80%. The presented scheme of particle/cell sorting would become a simple but versatile tool that is useful for general medical and biochemical experiments.