Abstract
The clinical utility of microfluidic techniques is often hampered by an unsatisfying sample throughput. Here, the effect of inertial forces on acoustofluidic particle sorting at high sample throughputs is investigated experimentally and theoretically. Polystyrene particles are acoustically prefocused to obtain precise trajectories. At increased flow rates it is observed that the particle stream is displaced towards the channel center, and above specific flow settings the particles spill over into the center outlet. This effect, coined the spillover effect, illustrates the complex interplay of viscous and inertial forces inside the microchannel. The effect is due to increased bending of the separatrices at the inlet and outlets and not due to the wall-lift force. The impact of the spillover effect on the separation of two different-sized particles is subsequently studied. Efficient sorting is done for subcritical splitting ratios and flow rates, but for close to critical settings or beyond, there is a breakdown of the acoustofluidic separation.
Highlights
Acoustophoretic particle manipulation in microfluidic systems, i.e., the active control of particles or cells by the means of acoustic waves, has been used to separate lipids from blood [1], rapidly control raw-milk quality [2], enrich tumor cells from blood samples [3], further reduce remaining white-blood-cell background through negative selection [4] and separate leukocyte subpopulations [5] amongst others
The effect of inertial forces on acoustofluidic particle sorting at high sample throughputs is investigated experimentally and theoretically
At increased flow rates it is observed that the particle stream is displaced towards the channel center, and above specific flow settings the particles spill over into the center outlet
Summary
Acoustophoretic particle manipulation in microfluidic systems, i.e., the active control of particles or cells by the means of acoustic waves, has been used to separate lipids from blood [1], rapidly control raw-milk quality [2], enrich tumor cells from blood samples [3], further reduce remaining white-blood-cell background through negative selection [4] and separate leukocyte subpopulations [5] amongst others. As with any microfluidic method, the sample throughput is key to a successful application. If rare cells, such as circulating tumor cells (CTCs) or CTC clusters, are to be isolated from a sample size of several milliliters, a whole-blood throughput in the hundreds of microliters per minute or higher should be achieved for the application to be relevant in the clinical setting. Whole-blood samples are diluted before processing through a microfluidic device, and it is useful to distinguish between the flow rate in the channel and the whole-blood throughput. Typical values for the per-channel whole-blood throughput in microfluidic applications are in the range of a few microliters per minute, and can reach more than 100 μl min−1
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