3- Semi-Empirical Estimation of Dean Flow Velocity in Curved Microchannels

Curved and spiral microfluidic channels are widely used in particle and cell sorting applications. However, the average Dean velocity of secondary vortices which is an important design parameter in these devices cannot be estimated precisely with the current knowledge in the field. In this paper, we used co-flows of dyed liquids in curved microchannels with different radii of curvatures and monitored the lateral displacement of fluids using optical microscopy. A quantitative Switching Index parameter was then introduced to calculate the average Dean velocity in these channels. Additionally, we developed a validated numerical model to expand our investigations to elucidating the effects of channel hydraulic diameter, width, and height as well as fluid kinematic viscosity on Dean velocity. Accordingly, a non-dimensional comprehensive correlation was developed based on our numerical model and validated against experimental results. The proposed correlation can be used extensively for the design of curved microchannels for manipulation of fluids, particles, and biological substances in spiral microfluidic devices.

Read More: Nature Scientific Reports, 2017, 7, 13655

2-Multiplex Inertio-Magnetic Fractionation (MIMF) of magnetic and non-magnetic microparticles in a microfluidic device

Separation of multiple microparticles at high throughput is highly required in different applications such as diagnostics and immunomagnetic detection. We present a microfluidic device for multiplex (i.e., duplex to fourplex) fractionation of magnetic and non-magnetic microparticles using a novel hybrid technique based on interactions between flow-induced inertial forces and countering magnetic forces in a simple expansion microchannel with a side permanent magnet. Separation of more than two types of particles solely by inertia or magnetic forces in a straight microchannel is challenging due to the inherent limitations of each technique. By combining inertial and magnetic forces in a straight microchannel and addition of a downstream expansion hydrodynamic separator, we overcame these limitations and achieved duplex to fourplex fractionation of magnetic and non-magnetic microparticles with high throughput and efficiency. Particle fractionation performance in our device was first optimized with respect to parameters such as flow rate and aspect ratio of the channel to attain coexistence of inertial and magnetic focusing of particles. Using this scheme, we achieved duplex fractionation of particles at high throughput of 109 particles per hour. Further, we conducted experiments with three magnetic particles (5, 11 and 35 µm) to establish their size-dependent ordering in the device under combined effects of magnetic and inertial forces. We then used the findings for fourplex fractionation of 5, 11 and 35 µm magnetic particles from non-magnetic particles of various sizes (10–19 µm). This Multiplex Inertio-Magnetic Fractionation (MIMF) technique offers a simple tool to handle complex and heterogeneous samples and can be used for affinity-based immunomagnetic separation of multiple biological substances in fluidic specimens in the future.

Read More: Microfuid Nanofuid, 2017, 21:83

1-Magneto-Hydrodynamic Fractionation (MHF) for continuous and sheathless sorting of high-concentration paramagnetic microparticles

Sorting cells, microorganisms and particles from a solution is of paramount importance in many biological applications. An ideal sorting device should work at high throughput, involve simple design, avoid energy consumption, operate without a diluting sheath flow and perform separation with high purity. However, currently available sorting methods such as pinched flow fractionation, hydrodynamic filtration, magnetophoresis and deterministic lateral displacement meet only a few of the above-mentioned characteristics. In this paper, we report a hybrid technique combining magnetic focusing of particles in a thin microchannel and their hydrodynamic fractionation at a downstream expansion region, to devise a sheathless and high-throughput Magneto-Hydrodynamic Fractionation (MHF) method. First, sheathless magnetic focusing of 11 μm microparticles against the wall of the thin microchannel was investigated over a wide range of flow rates (0.5–5 mL h−1). Then, a mixture of 5 μm and 11 μm paramagnetic particles was injected into the device at a flow rate of 5 mL h−1 to demonstrate their sorting. Both of these magnetic particles were aligned along the wall of the channel and hence focused in the device, however their centers were lying on different streamlines due to their different sizes. Therefore, they were separated into distinct streamlines upon entering into the expansion region. Using this device, we achieved a high throughput sorting of more than 104 particles per second with an approximate on-chip fractionation purity of 98%. This technique has a great potential for separation of more than two magnetic particles for application in immunomagnetic affinity-based sorting of multiple biological substances.

Read More: Biomedical Microdevices, 2017, 19:39