| Summary: | Blood consists of many components with different sizes, such as bacteria (~ 1 μm), platelets (~ 2 – 3 μm), red blood cells (RBCs, 6 – 8 μm) and neutrophils (~ 10 – 12 μm). In clinical diagnosis, isolating dysfunctional blood components requires manual and laborious centrifugation, which is not friendly to point-of-care applications. Herein, we have developed an automatable blood fractionation microfluidic device which can fractionate bacteria, RBCs, and neutrophils simultaneously. Two types of 2-staged cascaded spiral microfluidic devices were designed based on principles of Hi-Resolution (HiDFF) and Dean Flow Fractionation (DFF) reported previously. In design 1, small particles (e.g. bacteria) laterally migrated to inner wall of stage 1 junction were first sorted based on the HiDFF principle. At stage 2 junction, medium-sized particles (e.g. RBCs) migrating relatively slower were separated from the slowest large particles (e.g. neutrophils). In design 2, the stage 2 junction was modified based on the DFF principles, where larger particles were inertially focused at the inner wall while the medium-sized particles continued recirculating towards the outer wall at higher flowrates. Device characterisation was conducted using microscopic imaging of fluorescent microbeads, diluted blood, lysed blood, and purified neutrophils. In design 1, RBCs slightly overflowed into the neutrophil outlet due to high cell concentration in blood. In design 2, separation resolution was relatively lower due to reduced size difference between RBCs and deformed neutrophils under high flowrates. In future work, increasing stage 2 channel length of design 2 can improve separation resolution by reducing flowrates and minimizing neutrophil deformation.
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