Inertial focusing in triangular microchannels with various apex angles

Abstract

We consider inertial focusing of particles in channels with triangular cross sections. The number and the location of inertial focusing positions in isosceles triangular channels can change with varying blockage ratios (a/H) and Reynolds numbers (Re). In triangular channels, asymmetric velocity gradient induced by the sloped sidewalls leads to changes in the direction and the strength of the inertial lift forces. Therefore, varying the configuration (specifically, angle) of the triangular cross section is expected to lead to a better understanding of the nature of the inertial lift forces. We fabricated triangular microchannels with various apex angles using channel molds that were shaped by a planing process, which provides precise apex angles and sharp corners. The focusing position shift was found to be affected by the channel cross section, as expected. It was determined that the direction of the focusing position shift can be reversed depending on whether the vertex is acute or obtuse. More interestingly, corner focusing modes and splitting of the corner focusing were observed with increasing Re, which could explain the origin of the inertial focusing position changes in triangular channels. We conducted fluid dynamic simulations to create force maps under various conditions. These force maps were analyzed to identify the basins of attraction of various attractors and pinpoint focusing locations using linear stability analysis. Calculating the relative sizes of the basins of attractions and exhaustively identifying the focusing positions, which are very difficult to investigate experimentally, provided us a better understanding of trends in the focusing mechanism.

Changes of Inertial Focusing Position in a Triangular Channel Depending on Droplet Deformability and Size

“…The cross-sectional shape of a microchannel determines its velocity profile, which obviously can influence the inertial focusing positions. Triangular channels display unusual inertial focusing due to their unique velocity profile and the angles between channel walls [ 13 , 14 ]. The focusing positions change depending on particle size, vertex angles, and Re.…”

“…The equilibrium positions, or focusing positions, change with many parameters. Flow parameters (flow speed and viscoelasticity [ 9 , 10 , 11 ]), channel parameters (cross-sectional shape, aspect ratio, and channel curvature [ 12 , 13 , 14 , 15 , 16 ]), and particle parameters (size, shape, and deformability [ 17 , 18 , 19 ]) can be tuned to modulate the number and location of inertial focusing positions.…”

“…In particular, many interesting results have been reported with triangular cross-section channels [ 12 , 13 , 14 ]. The number and location of focusing positions are found to vary depending on the vertex angle, particle size, and Re.…”

Micromirror-Embedded Coverslip Assembly for Bidirectional Microscopic Imaging

“…Here, we constructed the master mold by a planing process (i in Figure 2a). The planing process is a high-precision machining technique that uses diamond cutting-tools to cut out a metal workpiece (Figure 2b) [29,30]. The planing process can provide a structure with precise angles and optically smooth surfaces [31][32][33].…”

High resolution and rapid separation of bacteria from blood using elasto‐inertial microfluidics

“…These methods either use the surface markers to isolate bacteria using affinity separation [14], or other properties such as their shape, size, deformability, density, electric or magnetic susceptibility, and hydrodynamic properties [15][16][17][18][19][20]. To this end, inertial microfluidics is attractive since the active and passive, sizebased, technology exploits inherent surface property and hydrodynamic forces that scale with increased flow rate and among them spiral channel designs have been shown to operate at extremely high volumetric flow rates (∼mL/min) [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. However, microfluidic technology has been utilized extensively to precisely focus and separate mammalian cells, including circulating tumor cells [34][35][36][37][38][39][40][41][42][43][44][45][46], but the separation of small-sized bacteria from blood has been challenging.…”