Fig 1.
Schematic of the droplet-based pressure control principle.
A mixing of particles of different sizes is injected in the right inlet of a DLD module. Particles larger than the critical diameter (Dc) are deviated towards the left outlet, while smaller particles flow in the right outlet. Each DLD outlet is connected to a T-junction with an oil inlet, for generation of droplets of lengths L1 and L2. Additional microfluidic modules are connected to the T-junction, with hydraulic resistances called respectively R1 and R2.
Fig 2.
a) Photograph of platform 1 showing the DLD silicon chip connected to a plastic cartridge with two independent T-junctions supplied by two oil inlets. b) Bright-field image of the DLD device with characteristic dimensions. The area located in the blue frame corresponds to the fluorescence image in c). c) Fluorescent streaks of 10 μm-beads at the DLD outlet. d) T-junctions connected to the DLD outlets and fluorescent profile of the channel containing the droplets.
Fig 3.
a) Photograph of platform 2 showing the DLD silicon chip connected to a plastic cartridge with two T-junctions supplied by the same oil inlet. b) Bright-field image of the DLD device with characteristic dimensions. The area located in the blue frame corresponds to the fluorescence image in c). c) Fluorescent streaks of 10 μm-beads at the DLD outlet. d) T-junctions connected to the DLD outlets.
Fig 4.
a) Photograph of platform 3, showing the connection of two DLD silicon chips (DLD1 and DLD2). One outlet of DLD1 is connected to the inlet of DLD2, while the other DLD1 outlet is connected to a T-junction in the cartridge. b) Schematic representation of platform 3. DLD1 deviates the largest red particles (> Dc1), while DLD2 separates the green (> Dc2) and the yellow (< Dc2) particles. The red particles are encapsulated in a T-junction, supplied by an oil inlet at an input pressure Po.
Fig 5.
a) Schematic representation of the cascaded configuration: the area located in the red frame corresponds to the images in b) and the area located in the green frame corresponds to the images in c) and d). b) 10 μm-bead streaks at the DLD1 outlet for three values of the oil pressure at the T-junction (Po). The left outlet of DLD1 is connected to a T-junction, while the right outlet is connected to a DLD2 module. c) Droplet generation at the T-junction connected to the DLD1 left outlet in condition n°2 (Po = 30 mbar). d) Droplet generation at the T-junction connected to the DLD1 left outlet in condition n°3 (Po = 60 mbar).
Fig 6.
Modeling of platform 3: R1 to R11 represent the hydraulic resistances of the microchannels in the cartridge and in the DLD chips.
P1 and P2 are the input pressures at the DLD1 entrance. Pb is the buffer pressure at the DLD2 entrance. Po is the input oil pressure at the T-junction. Q1, Q2, Qb and Qo are the flow rates in the DLD channels and in the T-junction.
Fig 7.
Schematic of the successive resolution steps.
Fig 8.
a) Experimental relation between the length ratio of the droplets (L/w, where w is the channel width) and the flow rate ratio (where Qw and Qo are the water and oil flow rates respectively). A linear fit is proposed from data obtained with a simplified T-junction geometry without DLD modules. This relation is then verified with the complete DLD cascaded platform, including the same T-junction geometry. b) Experimental relation between the oil input pressure Po and the oil flow rate Qo at the T-junction. The linear fit is again obtained from the simplified T-junction geometry and verified with the complete platform.
Fig 9.
Validation of the model on the complete DLD platform in two configurations.
10 Configuration 1 has a DLD1 module with 60 μm pillars (Dc1 = 20 μm) and a DLD2 module with 20 μm pillars (Dc2 = 15 μm), while configuration 2 has the same DLD1 module (Dc1 = 20 μm) but a DLD2 module of 5 μm pillars (Dc2 = 4 μm). 10 μm-beads are injected in configuration 1, while 5 μm-beads are injected in configuration 2. Input pressures P1 and P2 at the DLD1 entrance are chosen; then the buffer pressure Pb and oil pressure Po are calculated from the proposed model, by choosing a given droplet size ratio L/w. In both cases, the validity of the model is verified by measuring the droplet length at the T-junction (area n°1) and the particle distribution at the DLD1 inlet (area n°2) and outlet (area n°3) and at the DLD2 inlet (area n°4). Areas 1 to 4 are located on the schematic representations of the cascaded platform for both configurations.