Cell-based digital microfluidic chip for drug mixing and droplets generation: Design and simulation

Biological analysis in an on-chip flow cytometry is predictable, which often works with small volumes of reagents. A microfluidic chip to mix and encapsulate both living cells and drug in picoliter aqueous drops is proposed. By the aid of a counter-flow unit and a T-junction, this chip can mix cells with drugs, and form them into droplets of liquid in the moving air flow to isolate different trails of samples and keep the cells alive for a fixed time before measuring. Some simulation work was performed for optimizing the chip design. The relation between droplet length and flow rate ratio was found for a frequency in the range of 25-100Hz. The major stability in the droplet formation is reached at Q_d/Q_c=1, which correspond to a droplet length of 160μm. Droplets are separate by 170μm of air bubbles. The study also proposes an analysis of the pressure variation in water and air inlet during a period of droplet generation. Typically, the pressure over 25% or 80% respectively of the max pressure would be reached. The non-clogging counter-flow microconcentrator is used to improve efficiency of mixing. Solutions of water with 0.3mol/dm³ and 0.15mol/dm³ of glucose (respectively 4% and 2% glucose in water) were mixed in the tests. For equal flow-rates (25×10^-12 m³/s), it reaches a steady-state condition in the outlet with a concentration of 0.228mol/dm³. Since the droplets generator follows the micromixer in the chip, the outlet of micromixer is one of the inlets of the droplets generator. The size of the whole structure is less than 3mm, which allows them to be easily integrated into a developing flow-cytometry chip.