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In this paper, we describe the development of a microfluidic centrifuge with two inlets and two outlets potentially capable of rapidly separating nanoparticles and nanovesicles. Compared with the microfluidic centrifuge with a single inlet and outlet, the 2 ×2 microfluidic centrifuge gives improved centrifugation performance by increasing momentum flux transfer, angular velocity, and centrifugal acceleration. The center of flow rotation and the symmetry of the horizontal velocity in the microchamber were examined numerically. On the basis of the determined maximum velocity, the angular velocity and centrifugal acceleration were also evaluated. The centrifugation time of three different nanoparticles was examined by calculating the time when the nanoparticles left the microchamber for the first time. For visual observation and quantitative measurement of nanoparticle centrifugation, a 2 ×2 microfluidic centrifuge was fabricated and the experimental results demonstrate similar physical behavior to those of a mechanical centrifuge. On the basis of a comparison of the centrifugation time of two different nanoparticle populations of 300 and 700 nm in diameter, we propose that nanoparticles of different sizes can be physically separated by time under a range of inlet volume flow rates.

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The size-selective microfluidic separation of glass beads in a curved rectangular microchannel was fabricated in our previous work. In this study, we improve its separation performance and attempt an experimental visualization to examine the separation resolution. In the previous work, we found by visualization that the trajectory of 20 µm glass beads was influenced by their travelling path along a straight inlet channel. Using a forced sheath flow, a consistent bead trajectory along the middle of the straight inlet channel was obtained, and the sheath angle to minimize the focusing width of the flowing distributed beads was determined to be 45°. The physical explanation for the dynamic behavior of microbeads was elaborated. When the ratio of Stokes force to centrifugal force mainly acting on a glass bead fell under unity, the glass bead moved out to the wall in spite of the fact that its size was less than the height of the zero velocity position. To examine the separation resolution, the newly designed size-selective separation microchannel with the sheath was fabricated and its separation performance was visualized. The movement of the glass beads showed a good agreement with the separation mechanism explained by the force ratio. The resolution of the separation was visualized to be 10 µm for the size of glass beads used in the experiment. The size-selective separation performance was explained in terms of physical forces and was improved by solving the previous problems. A cascade device for the continuous separation of microbeads of various sizes can improve the separation resolution.

In this study, we demonstrate the preparation of nanocapsules using the self-assembly of preformed polymers at the interface of a three-way controlled laminated stream flow in a microchannel. The production process occurs without the use of surfactants and allows the regulation of nanocapsule size with solvent recycling. Problems associated with nanocapsule attachment to the channel surface disturbing the lamination flow and producing nanocapsules of poor quality were overcome by altering the microchannel aspect ratio. The aspect ratio was altered by considering the mixing ratio and velocity distribution on the cross section along the microchannel. Modeling and practical experiment identified the aspect ratio of the microchannel of 1.6 as producing clear lamination flow. Ovalbumin-encapsulated nanocapsules were produced with a narrow size distribution of \200 nm, allowing standard bacterial filtration processes to be used to sterilize the nanocapsules. To obtain a concentrated preparation of protein nanocapsules with minimal solvent contamination, a three-outlet separation system was developed. Using a diffuser with a diverging angle on the outlet collection port, we were able to focus 95% of the nanocapsules into the central collection channel with the PLGA acetone fraction into the side channels from which they could be collected and the components recycled. Liquid phase 1 H NMR analysis indicated that the lyophilized nanocapsules do not contain detectable acetone.