Inertial focusing in triangular microchannels with various apex angles.

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.

Shaped 3D microcarriers for adherent cell culture and analysis.

Standard tissue culture of adherent cells is known to poorly replicate physiology and often entails suspending cells in solution for analysis and sorting, which modulates protein expression and eliminates intercellular connections. To allow adherent culture and processing in flow, we present 3D-shaped hydrogel cell microcarriers, which are designed with a recessed nook in a first dimension to provide a tunable shear-stress shelter for cell growth, and a dumbbell shape in an orthogonal direction to allow for self-alignment in a confined flow, important for processing in flow and imaging flow cytometry. We designed a method to rapidly design, using the genetic algorithm, and manufacture the microcarriers at scale using a transient liquid molding optofluidic approach. The ability to precisely engineer the microcarriers solves fundamental challenges with shear-stress-induced cell damage during liquid-handling, and is poised to enable adherent cell culture, in-flow analysis, and sorting in a single format.