Exploring operational boundaries for acoustic concentration of cell suspensions.

The development of a standardized, generic method for concentrating suspensions in continuous flow is challenging. In this study, we developed and tested a device capable of concentrating suspensions with an already high cell concentration to meet diverse industrial requirements. To address typical multitasking needs, we concentrated suspensions with high solid content under a variety of conditions. Cells from Saccharomyces cerevisiae, Escherichia coli, and Chinese hamster ovary cells were effectively focused in the center of the main channel of a microfluidic device using acoustophoresis. The main channel bifurcates into three outlets, allowing cells to exit through the central outlet, while the liquid evenly exits through all outlets. Consequently, the treatment separates cells from two-thirds of the surrounding liquid. We investigated the complex interactions between parameters. Increasing the channel depth results in a decrease in process efficiency, attributed to a decline in acoustic energy density. The study also revealed that different cell strains exhibit distinct acoustic contrast factors, originating from differences in dimensions, compressibility, and density values. Finally, a combination of high solid content and flow rate leads to an increase in diffusion through a phenomenon known as shear-induced diffusion. KEY POINTS: • Acoustic focusing in a microchannel was used to concentrate cell suspensions • The parameters influencing focusing at high concentrations were studied • Three different cell strains were successfully concentrated.

Rail configuration for lateral particle transport across intact co-flows: effect of wall and rail geometry on liquid and particle transport.

Layer-by-Layer coating technology is of great importance for many applications of microparticles whereby exposure of the particles to various reagents is needed. Mutual contamination of the reagents during this process is a key challenge, and this undesired effect should be avoided. Here we introduce a device that provides subsequent exposure of particles to various liquids and minimizes mixing of the liquids at the same time. The key element of the device is a rail (groove) at the bottom of a microfluidic channel. The rail forms an angle (between 0 and 90 degrees) and thus enables passive transport of particles through the intact co-flows of the different fluids. To avoid the undesirable effect of reagent stream mixing, internal walls are introduced to separate the different flows. Various designs of the proposed device are considered, and their performance is experimentally analyzed.

Rail induced lateral migration of particles across intact co-flowing liquids.

This paper presents a rail guided method to apply a Layer-by-Layer (LbL) coating on particles in a microfluidic device. The passive microfluidic approach allows handling suspensions of particles to be coated in the system. The trajectory of the particles is controlled using engraved rails, inducing lateral movement of particles while keeping the axially oriented liquid flow (and the interface of different liquids) undisturbed. The depth and angle of the rails together with the liquid velocity were studied to determine a workable geometry of the device. A discontinuous LbL coating procedure was converted into one continuous process, demonstrating that the chip can perform seven consecutive steps normally conducted in batch operation, further easily extendable to larger cycle numbers. Coating of the particles with two bilayers was confirmed by fluorescence microscopy.