An automated microdroplet passive pumping platform for high-speed and packeted microfluidic flow applications

Abstract

Surface tension driven passive pumping is a microfluidic technology that uses the surface tension present in small droplets to generate flow. To enhance the potential of this type of passive pumping, a new 'micro passive pumping' technique has been developed that allows for high throughput fluidic delivery by combining passive pumping with a small droplet-based fluidic ejection system. Flow rates of up to four milliliters per minute (mL/min) were achieved that are solely limited by the channel geometry and droplet size. Fluid exchange rates can be performed within tens of milliseconds (ms) by delivering fluids from multiple nozzles. The technique can be extended to a multitude of platforms, as channels are not pressurized and therefore do not require bonding to a substrate. This technique provides a novel flow control for high-speed and packeted flow applications without requiring external tubing connections or substrate bonding.

Fig. 1

Intrachannel fluid velocities when (a) the inlet diameter is equal to the channel width and (b) the inlet diameter is constant at 1 mm.

Fig. 2

(a) Schematic of two nozzles aimed at inlet. Insert: Delivered volume as a function of open time at different pressures. (b) Top view picture of two nozzles aimed at inlet and a drop placed at the outlet. Device dimensions are 2.2 mm, 7.5 mm, 250 µm (width, length, height).

Fig. 3

Upper left: Average fluid velocity inside a channel as a function of time as caused by the placement of a single drop, manually or otherwise, at the channel inlet. Bottom left: schematic of drop collapse. (a)–(h) Drop collapse time steps corresponding to the schematic.

Fig. 4

Red fluorescent polystyrene microspheres in channel. While some beads are adhered to the PDMS, most flow towards the outlet and then undergo a small backflow towards the inlet. The tail produced by the fluorescent beads shows the direction of flow.

Fig. 5

Fluidic exchange inside a channel taken by slow motion recording with a high speed camera.