Abstract
We report a capillary flow-driven microfluidic device for blood-plasma separation that comprises a cylindrical well between a pair of bottom and top channels. Exposure of the well to oxygen-plasma creates wettability gradient on its inner surface with its ends hydrophilic and middle portion hydrophobic. Due to capillary action, sample blood self-infuses into bottom channel and rises up the well. Separation of plasma occurs at the hydrophobic patch due to formation of a ‘self-built-in filter’ and sedimentation. Capillary velocity is predicted using a model and validated using experimental data. Sedimentation of RBCs is explained using modified Steinour’s model and correlation between settling velocity and liquid concentration is found. Variation of contact angle on inner surface of the well is characterized and effects of well diameter and height and dilution ratio on plasma separation rate are investigated. With a well of 1.0 mm diameter and 4.0 mm height, 2.0 μl of plasma was obtained (from <10 μl whole blood) in 15 min with a purification efficiency of 99.9%. Detection of glucose was demonstrated with the plasma obtained. Wetting property of channels was maintained by storing in DI water under vacuum and performance of the device was found to be unaffected over three weeks.
Highlights
Response of cells to various biophysical effects
A microfluidic device which employed asymmetric capillary flow, which was realized by surface modification of one of the channel walls using spray coating of silica nanobead multilayers, was used for blood plasma separation[26]
Degassing of channel in the microfluidic device using vacuum desiccator to enable the flow of sample blood into the microchannel device was reported[27,28]
Summary
Response of cells to various biophysical effects. Such devices are advantageous due to simpler design, ease of fabrication, continuous operation and low cost[22]. As the capillary flow velocity decreases with rise in meniscus height, the cells tend to sediment due to their higher density while the blood plasma rise up the well by capillarity due to its significantly lower viscosity (about 2.5 times[32]). By this combined effect of gravity and capillarity, separation of plasma from blood commences. The separated plasma flows into the upper microchannel, where detection of analytes could be performed
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