Modular off-chip emulsion generator enabled by a revolving needle

Abstract

Microfluidics chips have demonstrated unparalleled abilities in droplet generation, including precise control over droplet size and monodispersity. And yet, their rather complicated microfabrication process and operation can be a barrier...

OsciDrop: A Versatile On-demand Droplet Generator

“…19 reported an off-chip droplet generator enabled by a 34G needle and a spanning conical frustum; however, the large conical frustum limited its use in small containers, such as centrifuge tubes. Although alternative methods, using a revolving needle for generating microdroplets in a centrifuge tube, have been presented, 18, 21 they induced strong vortices that consequently undermine their utilities in miniaturized containers like microwells of the multi-well plate due to generated droplets could be smashed by vortices. 21 Other two capillary-based approaches circumvented this limitation but showed narrow monodisperse ranges and difficulties in droplet size control.…”

“…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.…”

“…Recently, chip-free droplet generation methods, such as centrifugal emulsification 23, 24 and capillary/needle-based approaches, 18, 20, 22, 23 emerge as promising alternatives for generating droplets on demand without microfabrication. For instance, using a bench-top centrifuge with the aid of a micro-nozzle array to generate water-in-oil (w/o) droplets has been utilized for digital polymerase chain reaction (PCR), reducing the complexity of droplet assays.…”

“…26 Similar approaches, such as generating droplets on demand by spinning, 19 revolving, 16 or beveled 23 capillaries/needles, have displayed potential for widespread adoption due to reduced cost and experimental difficulties. Nevertheless, these methods require manual pre-processing of the dispensing capillary ( e.g ., cutting, beveling, heating, and stretching) 18, 20, 23, 27 or connecting the capillary with tubing using capillary wax or epoxy glue, 18,20 which is not readily manufacturable. Therefore, a chip-free droplet generation method using easily accessible instruments without manual pretreatment and assembling is attractive.…”

Continuous Embedded Droplet Printing in Yield‐Stress Fluids for Pharmaceutical Drug Particle Synthesis

“…Because of these beneficial qualities, embedded droplet printing has demonstrated unique functionality in a wide variety of fluidic manipulation applications including chemical synthesis and screening, biological assays, and particle synthesis. There are many techniques for droplet generation and processing including open and off‐chip microfluidic systems, [ 13,14 ] in‐air microfluidics, [ 15 ] and droplet formation and deposition at a fluid interface. [ 16–19 ] However, embedded droplet printing is the only method (other than a microgravity environment) that allows for droplet processing in an “absolutely quiescent” state, namely the elimination of exterior convective forces as well as essentially indefinite spatial isolation of droplets from each other and from any boundaries of the bath material.…”