Characterization of passive microfluidic mixer with a three-dimensional zig-zag channel for cryo-EM sampling

Abstract

Microfluidic mixing is an essential unit operation in miniaturized analytical systems. Achieving high mixing efficiency is considerably difficult in conventional microfluidic micromixers because the fluid flow is generally associated with a laminar flow regime and is dominated by molecular diffusion. In this study, different microfluidic passive mixer devices are designed, simulated, and tested. Passive microfluidic mixers, such as straight, 2D zig-zag, and 3D zig-zag geometries, are evaluated to assess the mixing efficiency of each layout. The mixing performance is investigated, and the comparison of experimental results with computational simulations determines the mixing efficiencies. We characterized the 3D zig-zag channel to perform a promising design for improving mixing in a microfluidic passive mixer device and can be optimized to enhance mixing efficiency by the appropriate length of the microfluidic mixer. A passive micromixer with a 3D zig-zag channel is further demonstrated by characterizing mixing at varying Reynolds numbers of 18.5 ≤ Re ≤ 55.5. Finally, we validate the utility of the mixing device for the screening of detergents for a preferential orientation issue of influenza A virus hemagglutinin protein particles in cryo-EM integrated with a microfluidic spraying approach. The results reported here are versatile, reproducible, and readily adaptable to various fields needing a fast and reliable aqueous phase mixing strategy.