Design and characterization of a capillary-driven and parallelized microfluidic chip for distributing a liquid plug

To realize a portable, capillary-driven, and parallelized microfluidic chip, how to evenly distribute a liquid plug from the inlet to multiple daughter microchannels is a challenging task. Two approaches were adopted to generate sufficient capillary pressure to allow a liquid plug spontaneously flowing through bifurcation features, including enlarging the contact perimeter between the liquid plug and microchannel walls and applying hydrophilic coating to the microchannel walls. A 1-to-2 bifurcation microfluidic chip and a 1-to-4 bifurcation microfluidic chip were designed and fabricated on PMMA substrates for experiments. Initially red food dye was used to demonstrate the effectiveness of the chips, and experiment results revealed that the 1-to-2 microfluidic chip is capable of 100% liquid splitting efficiency with a CV of 5.7% whereas the 1-to-4 microfluidic chip is capable of 83% liquid splitting efficiency with a CV of 6.7%. After successfully conducting experiments with red food dye, human whole blood and blood plasma were introduced into the 1-to-2 microfluidic chips and splitting efficiency was investigated. The experiment results showed a 33% and 67% splitting efficiency for human whole blood and blood plasma, respectively. And the lower splitting efficiency can be attributed to the complex and Non-Newtonian fluidic property of the blood.