Performance Assessment and Improvement of a Spilt-and-Recombine Micromixer for Immunomagnetic Cell Sorting

Abstract

Performance of a split-and-recombine micromixer (Tan et al., 2005) is assessed by means of numerical simulation. The micromixer is designed for micro cell sorting systems using immunomagnetic beads, of which working principle is lamination of fluid layers. The fluid motion in a complex three-dimensional geometry is simulated by using the finite difference method and the motion of beads is dealt with the one-way coupling Lagrangian particle tracking method. Although the thickness of laminated layers should ideally reduce by the factor of 2 n (where n is the number of unit-mixers connected in series), the present simulation with a realistic geometry shows that the thickness does not reduce that much. Relatively large unmixed regions are formed in the central region, which deteriorate the mixing performance. The size of the unmixed regions and the degree of mixing are quantitatively investigated. Based on the observation, an improved mixer arrangement is proposed. While the original arrangement proposed by Tan et al. (2005) was to simply connect identical unit-mixers, the present arrangement is to alternately connect the original unit-mixer and one with the mirrored geometry. With this modified arrangement, the unmixed region is suppressed and better mixing is achieved.