A simple capillary-based open microfluidic device for size on-demand high-throughput droplet/bubble/microcapsule generation

Abstract

We report an easily-established capillary-based open microfluidic device (COMD) as a simple and robust method for size on-demand generation of monodisperse droplets of various fluidic materials with controllable volume. A device is set up in which a capillary is positioned with its tip close to a flat surface with a precise gap distance in a container. The continuous phase remains static in the container, and the dispersed phase is pumped through the capillary and forms droplets at the exit of the gap. Monodisperse droplets, bubbles and microcapsules of various fluids with diameters of 10-300 μm (picoliter to nanoliter) and generation frequency of 1-1000 Hz are obtained by controlling the gap distance in the range of 5-500 μm. The droplet formation is caused by capillarity-induced narrowing of the dispersed phase at the capillary exit, with droplet size being determined by the gap volume and fluid flow. We find that, at low flow rate, using the same COMD, the generated droplet size is constant, being determined by the gap size; however, at higher flow rate, droplet size increases with the flow rate. Droplet types can be managed by fluids and surface modification of the capillary and bottom surfaces. High throughput droplet generation is achieved by in-parallel integration of multiple capillaries in one device. Such a COMD is simple and easy-to-build without complex microfabrication requirements; however, it is highly robust, flexible and easy-to-operate for size on-demand droplet generation. It offers an opportunity for common laboratories to perform droplet-based assays, and has high potential for high throughput industrial emulsification applications as well.

Advances in passively driven microfluidics and lab-on-chip devices: a comprehensive literature review and patent analysis

“…Capillary action was used as a portable sidewall of another microchannel with controllable size. 179 Kim et al described a liquid additive, which passively controlled the velocity of cells within a detectable range during capillary sample loading, thereby eliminating the need for bulky and expensive pumping equipment. It also required the adoption of an immune bead assay, which was quantied with a portable uorescence cell counter based on a blue-light-emitting diode.…”

OsciDrop: A Versatile On-demand Droplet Generator

“…7–10 T-junction and flow-focusing designs are commonly used for droplet generation due to geometrical simplicity. 11–16 Unfortunately, chip-based droplet microfluidics suffers from the following drawbacks: 1) the devices are usually fabricated using time-consuming, labor-intensive photolithography and etching process with cost-prohibitive specialized equipment in cleanrooms; 17–20 2) the chip fabrication and operation are complicated, which is a technical barrier for inexperienced researchers; 18,19,21 3) it is difficult to precisely define droplet volumes by using multiple pumps and synchronizing several factors ( e.g ., flow rate, fluid viscosity, channel geometry, and surface tension); 20, 22 These limitations hinder the prevalence of chip-based droplet generation.…”

Scalable Production of Monodisperse Functional Microspheres by Multilayer Parallelization of High Aspect Ratio Microfluidic Channels

“…Many attempts have been made to operate the microfluidic droplet generators in parallel to enhance the throughput of production [16,17]. In flow-focusing [18] or T-junction [19] type geometries, as the droplet break-up is induced by the viscous shearing force of the two phase flows, the pressure fluctuations may cause instability of the shear force and result in polydispersed droplets [20].…”