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Download as PDFParticle Behavior inside Planar Straight and Spiral Microchannels
Although inertial force-induced lateral migration has been extensively studied for almost 50 years and has been utilized in various microchannels to perform size-based separation for cell research, the mechanism of inertial focusing is generally described as the interplay between inertial lift force and dean drag force and lacks information on particle behavior in depth direction, leaving several missing pieces from the physical understanding of inertial focusing parameter space [1] [2] [3] . Here we present an exploratory study of inertial focusing in planar straight microchannels and spiral microchannels with varying geometry to identify the regimes of particle behavior in response to flow rate and channel dimension. To gather accurate information on the depth direction of a straight channel, we fabricated a pair of straight channels with the same cross-sectional dimensions but different orientations and recorded the focusing positions of particles in the top-down images under the same conditions using these two devices, respectively. Combining the data from these two channels provides unambiguous information on the cross-sectional particle focusing positions. We also developed a polymer-casting technique to fabricate PDMS devices with smooth sidewalls through which one can observe the particle positions at the outermost loop of the planar spiral in the channel depth direction. The data gathered for the same spiral channel but from different directions allowed us to map the distribution of particles in cross-section with a simulated velocity field. With accurate information on particle positions in the cross-sections of straight and spiral channels, we would be able to relate the effect of channel dimension on the force field with the related particle- focusing behavior and identify the key parameters for the optimal design of a size-based separation device targeted at specific size range.
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- Figure 1: Top-down views of fluorescent streak images of flowing 15.5-μm-diameter particles at the outlet 4 cm downstream of straight channels with rectangular cross-section as a function of channel Reynolds number, ReC. (A): 100 μm x 50 μm; (B): 50 μm x 100 μm; (C): cross-sectional focusing locations.
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- Figure 2: The focusing positions of 15.5-μm-diameter particles in spiral channels with rectangular cross-section of 500 μm x 95 μm as a function of flow rate. The box with blue dash line in (A) represents the location for microscope observations. Yellow line on the right of channel cross-section in (B) represents the inner wall of spiral channel.
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