Schematic illustration of the developed microfluidic device for pathogen removal from blood. (a) The design consists of two cascaded straight microchannels (20 × 20 µm (W × H), 5 mm long for first channel and 1 mm long for the cascaded channel) with two bifurcations (1:8:1) in series. The cascaded design allows removal of bacteria at each bifurcation, thereby achieving a 2-stage bacterial removal in a single step. (b) Cross-sectional and top view of the microchannel illustrating the separation principle. As blood flows through the channel (margination region), deformable RBCs migrate axially to the channel centre, resulting in margination of other cell types (bacteria, platelets, and leukocytes) towards the channel walls and subsequently removed from the side outlets while the centre outlet collects the bacteria-depleted blood.
Effect of microchannel height (aspect ratio) on bacteria margination. (a) Bacteria concentration in the filtered centre outlet with varying channel heights using a single margination channel of 15 mm length and 20 µm width (schematic single channel design in red box). Bacteria concentration was normalized with sample to determine the percentage of bacteria remaining after filtration. (b) Fluorescent intensity Z-profiles at the outlet centre region of 20 µm and 75 µm height channels and corresponding schematic illustration of their bacteria margination. Confocal images at the mid plane of 20 µm and 75 µm height channels indicate less efficient bacteria margination at the mid plane region of high aspect ratio channel.
Effect of flow rate on bacteria margination. (a) Normalized bacteria concentration in the filtered centre outlet for increasing flow rate. Bacteria separation efficiency improved as flow rate increases but remained approximately constant beyond 10 µl min−1. Averaged composite images of the bifurcation indicate increase in concentration of FITC-conjugated bacteria at the channel sides with increasing flow rates. (b) Optical images illustrating the enhanced cell free layer at the expanded bifurcation. Most of the marginated bacteria reside within the cell free layer next to the channel wall which allows their efficient removal from the side channels, while the densely packed RBCs are filtered into the larger centre outlet with minimal loss.
Device characterization of the cascaded design. (a) Averaged fluorescence composite images at the margination channel (20 µm × 20 µm) and corresponding intensity linescans illustrating the larger number of FITC-conjugated bacteria found at the channel sides after margination. Dotted lines indicate the approximate position of channel walls. (b) Optical images and plot of bacteria filtration efficiency at different stages. Experimental results were similar to the theoretical separation efficiencies calculated based on the bifurcation ratio (blue region in schematic) and the complete bacteria margination to the four channel walls. A high bacteria separation efficiency of >80% was achieved at the collected centre outlet after two stages of filtration (enhanced online). [URL: http://dx.doi.org/10.1063/1.4710992.1]10.1063/1.4710992.1
Spiked whole blood analysis. (a) Normalized concentration of different cellular components at the filtered centre outlet using human whole blood spiked with E. coli and S. cerevisiae separately. RBCs concentration increased by ∼30% as more RBCs were packed at the centre due to Fahreaus effect. Inflammatory cellular components (platelets and leukocytes) and microbes undergo margination to the channel sides, resulting in >80% decrease in concentration at the centre outlet. Optical images (100× magnification) of each component are indicated at the top of their corresponding histogram bar. (b) Optical images illustrating yeast filtration at different stages. The larger yeast (∼5 µm) undergoes margination to the four corners in the straight channel (red arrows), resulting in complete margination to the sides and thus higher separation efficiency (enhanced online). [URL: http://dx.doi.org/10.1063/1.4710992.2]10.1063/1.4710992.2
High throughput blood filtration using a parallel system. (a) Schematic layout of the device consisting of an additional filter region to remove clogs and debris and 6 channels with cascaded design in parallel to achieve higher flow rates. (b) Experimental results indicating similar device performances as compared to single channel in removal of different blood components and bacteria using the parallel system at 100 µl/min.
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