Blood plasma separation in microchannels is a key element in microfluidics-based biodetection and lab-on-chip technology. In microfluidics, acoustophoresis-based blood plasma separation is considered one of the most efficient approaches for high-throughput separation. However, the physics of the separation of plasma from whole blood (dense suspension) by using acoustophoresis is not well understood. In this paper, we provide improved understanding of blood plasma separation from whole blood using acoustophoresis based on experiments and simulations. The interplay between the acoustophoretic timescale ${\tau }_{\mathrm{ACP}}$ and shear-induced diffusion timescale ${\tau }_{\mathrm{SID}}$ that represents the underlying mechanism of the focusing of cells and separation of plasma is illustrated. The results show that, for whole blood, ${\tau }_{\mathrm{SID}}\ll {\tau }_{\mathrm{ACP}}$; thus, acoustophoresis fails to concentrate the cells and form a cell-free plasma layer. Serial extraction of concentrated cells from the center of the channel gives rise to ${\tau }_{\mathrm{SID}}\gg {\tau }_{\mathrm{ACP}}$, thus enabling the focusing of cells and formation of the plasma layer. Blood plasma separation in the acoustophoretic device is simulated using a simple 2D model that employs the mixture theory. Based on the improved understanding, we develop an acoustophoretic device that is capable of separating $22\mu \mathrm{l}/\min$ plasma from $100\mu \mathrm{l}/\min$ of whole blood (at 40% hematocrit), offering significantly higher plasma throughput and recovery (36.67%) compared to devices reported previously by Lenshoff et al. [1] and Tajudin et al. [2]. Finally, we present a rule of thumb for the design of acoustophoretic devices for different hematocrit concentrations to offer the desired plasma throughput and recovery.

• Received 2 March 2018
• Revised 4 May 2018

DOI:https://doi.org/10.1103/PhysRevApplied.10.034037