• Best customer support

  • Payment via invoice or credit card

  • WORLDWIDE EXPRESS SHIPPING

  • Flow Control
    • Baoding Shenchen
    • Bartels
    • DK Infusetek
    • Elveflow
    • Harvard Apparatus
    • HNP Mikrosysteme
    • Ismatec
    • Jun-Air
    • LabTech
    • Longer
    • Masterflex
    • New Era
  • Chips & Microfabrication
    • BlackHole Lab
    • Droplet Genomics
    • Grace Bio-Labs
    • iBioChips
    • IVTech
    • KemLab
    • MesoBioTech
    • microfluidic ChipShop
    • Micronit
    • SynVivo
  • Imaging
    • Fastec Imaging
    • Nikon
    • Phantom (Ametek)
    • Photron
    • Pixelink
    • Zeiss
  • Accessories
    • BD
    • Diba
    • Elveflow
    • Emulseo
    • Hamilton
    • Saint-Gobain
  • Sensors
    • Elveflow
    • MicruX
    • Sensirion
    • Zimmer & Peacock
  • Valves
    • Bürkert
    • Elveflow
    • Memetis
  • Contact Us
  • Register or Sign in
0
Darwin Microfluidics
  • CHIPS & BIO
    Droplet Generators
    • Flow Focusing
    • T-Junction
    • Co-Flow
    • Drop-seq (scRNA-seq)
    Micromixers
    Organ-on-a-Chip
    • Chips
    • Bundles
    • Accessories
    Cell Sorting / Trapping
    Enhanced Oil Recovery
    Flow Cells
    Chip Holders
  • FLOW CONTROL
    Syringe Pumps
    • Syringe Pump Systems
    • OEM Modules
    • Syringes
    • Accessories
    Pressure Control
    • Pressure Controllers
    • Reservoirs & Accessories
    Peristaltic Pumps
    • Systems & Drives
    • Pump Heads
    • Tubing
    • Accessories
    Miniature Pumps
    • Gear Pumps
    • Piezo Pumps
    Valves
    • Solenoid Valves
    • Miniature SMA Valves
    • Manual Valves
    • Rotary Valves
    Sensors
    • Flow Sensors
    • Pressure Sensors
    Compressors & Vacuum Pumps
  • IMAGING
    Cameras
    • USB Cameras
    • High-speed Cameras
    Microscopes
    • Inverted Microscopes
    • Stereo Microscopes
  • ACCESSORIES
    Bubble Traps
    Tanks & Reservoirs
    Tubing
    • PTFE, PEEK, FEP Tubing
    • Silicone & Tygon Tubing
    • Tubing with stoppers
    Assortment Kits
    Syringes & Needles
    • Syringes
    • Needles & Couplers
    Oils & Surfactant
    Surface Treatments
    Fittings & Connectors
    • Threaded Fittings
    • Luer Fittings
    • Barbed Fittings
    • Sleeves & Ferrules
    • Splitters & Manifolds
    Filters
    Check Valves
    Microfabrication
    • Soft-lithography Systems
    • PDMS
    • Photoresists
    • Wafers
    • Punchers
    • Chip Prototyping Tools
(+33) 189 197 051 contact@darwin-microfluidics.com
Browse By Brand
  • Flow Control
    • Baoding Shenchen
    • Bartels
    • DK Infusetek
    • Elveflow
    • Harvard Apparatus
    • HNP Mikrosysteme
    • Ismatec
    • Jun-Air
    • LabTech
    • Longer
    • Masterflex
    • New Era
  • Chips & Microfabrication
    • BlackHole Lab
    • Droplet Genomics
    • Grace Bio-Labs
    • iBioChips
    • IVTech
    • KemLab
    • MesoBioTech
    • microfluidic ChipShop
    • Micronit
    • SynVivo
  • Imaging
    • Fastec Imaging
    • Nikon
    • Phantom (Ametek)
    • Photron
    • Pixelink
    • Zeiss
  • Accessories
    • BD
    • Diba
    • Elveflow
    • Emulseo
    • Hamilton
    • Saint-Gobain
  • Sensors
    • Elveflow
    • MicruX
    • Sensirion
    • Zimmer & Peacock
  • Valves
    • Bürkert
    • Elveflow
    • Memetis
  • Get a Quote
  • 0
  • CHIPS & BIO
    Back
    Droplet Generators
    • Back
    • Flow Focusing
    • T-Junction
    • Co-Flow
    • Drop-seq (scRNA-seq)
    Micromixers
    Organ-on-a-Chip
    • Back
    • Chips
    • Bundles
    • Accessories
    Cell Sorting / Trapping
    Enhanced Oil Recovery
    Flow Cells
    Chip Holders
  • FLOW CONTROL
    Back
    Syringe Pumps
    • Back
    • Syringe Pump Systems
    • OEM Modules
    • Syringes
    • Accessories
    Pressure Control
    • Back
    • Pressure Controllers
    • Reservoirs & Accessories
    Peristaltic Pumps
    • Back
    • Systems & Drives
    • Pump Heads
    • Tubing
    • Accessories
    Miniature Pumps
    • Back
    • Gear Pumps
    • Piezo Pumps
    Valves
    • Back
    • Solenoid Valves
    • Miniature SMA Valves
    • Manual Valves
    • Rotary Valves
    Sensors
    • Back
    • Flow Sensors
    • Pressure Sensors
    Compressors & Vacuum Pumps
  • IMAGING
    Back
    Cameras
    • Back
    • USB Cameras
    • High-speed Cameras
    Microscopes
    • Back
    • Inverted Microscopes
    • Stereo Microscopes
    • Back
    • Back
  • ACCESSORIES
    Back
    Bubble Traps
    Tanks & Reservoirs
    Tubing
    • Back
    • PTFE, PEEK, FEP Tubing
    • Silicone & Tygon Tubing
    • Tubing with stoppers
    Assortment Kits
    Syringes & Needles
    • Back
    • Syringes
    • Needles & Couplers
    Oils & Surfactant
    Surface Treatments
    Fittings & Connectors
    • Back
    • Threaded Fittings
    • Luer Fittings
    • Barbed Fittings
    • Sleeves & Ferrules
    • Splitters & Manifolds
    Filters
    Check Valves
    Microfabrication
    • Back
    • Soft-lithography Systems
    • PDMS
    • Photoresists
    • Wafers
    • Punchers
    • Chip Prototyping Tools
  • Call
  • Contact
  • Store info

172 rue de Charonne
Bâtiment B1, 1er étage
Paris, France

  • Darwin MicrofluidicsHome
  • Reviews
  • The most used designs for droplet generation in microfluidics

The most used designs for droplet generation in microfluidics

  • Reviews
  • 27 Oct, 2020
  • Posted by: Christelle ANGELY

Platforms based on microfabrication and microfluidics have been successfully utilized in a variety of applications such as drug discovery, polymer chain reaction (PCR), single-cell analysis or crystallization proteins to name a few. For all of these applications, producing droplets at controlled sizes as well as controlled generation rates appear as key factors in order to obtain interpretable, reliable and robust results. Indeed, droplet size can be affected by many factors such as interfacial tension or channel size.

Today, a wide range of geometries have been developed, allowing the generation of droplets in passive or active mode. In this review, we will focus on the most widely used droplet generation designs.

Passive and active modes

Passive mode

Microfluidic methods for forming droplets can be either passive or active. In passive methods, microfluidic two-phase flow is controlled by syringe pumps (that supply constant flow rates) or pressure regulators without additional energy input. During droplet formation, a part of the energy introduced from the syringe pumps or pressure controllers is converted into interfacial energy and thus facilitates the destabilization of the liquid-liquid interface, whereby discrete droplet shedding from the dispersed phase occurs [Seemann R. et al. 2012 Rep Prog Phys.]. Pratically, the fluid phase to be dispersed is driven into a microchannel by a pressure-driven flow in which the volume flow rate or the applied pressure is necessarily controlled. A second immiscible liquid is driven into a separate microchannel via an independently controlled flow. The two streams meet at the junction. The geometry of the junction and the volumetric flow rates of the two fluids determine the flow field, which deforms the interface [Christopher GF and Anna SL. 2007 J Phys Appl Phys].

Active mode

In active mode, it is possible to modulate the droplet generation with an additional energy input by active controls including external forces such as electric, magnetic or centrifugal fields and internal forces like viscous and capillary forces. To be more precise, the energy imbalance modulates the nature of force balance on the interface for droplet generation.

The active droplet generation can either be induced by two types of forces: the modification intrinsic forces or the introduction of additional forces. Additional forces are exploited by applying external electric, magnetic and centrifugal fields, while modifying the intrinsic inertial, viscous and capillary forces can be performed by manipulating the dynamic velocity and material properties, including viscosity, interfacial tension, channel wettability, and fluid density [Chong ZZ et al. 2016 Lab Chip.].

Droplet generation chip designs

Cross-flow with T-junction

We can talk about cross-flow when dispersed and continuous phase fluids meet at an angle θ between 0 and 180° (see Fig. 1). Generally, the cross-flow structure is associated to a T-junction. Thus, the dispersed and continuous fluids are fed orthogonally.

There are three regimes of microfluidic droplet generation with T-junction: the dripping regime, the squeezing regime and the jetting regime (see Fig. 2). In principle, droplets generated with dripping mode are smaller than the channel dimension and highly monodisperse. For squeezing regime, droplets are larger than the channel and monodisperse. Finally, with the jetting mode, the droplet generation is polydisperse.

The first advantage of the cross-flow is the ease with which droplets can be formed and the uniformity of the resulting droplets. Indeed, within a large range of flow rates, it is possible to obtain a regular and periodic droplet formation when a single T-shape channel is used. However, in some studies [Garstecki P et al. 2005 Nature Phys ; Barbier et al. 2006 Phys Rev.], it appears that droplets are not necessarily regular when multiple droplet generators are coupled with a single set of syringe pumps, that can appear as a critical issue in the case of a study where it is necessary to precisely control the droplet size.

Cross-flow chip designs

Figure 1 : Schematic of various microfluidic device geometries (not to scale). (a) Cross-flow. (i) “T-junction” where the continuous and dispersed phase fluids meet perpendicularly (θ = 90°). (ii) “T-junction” in which the two fluids intersect at an angle θ (0° < θ < 90°). (iii) “Head-on” geometry (θ = 180°). (iv) Y-shaped junction with intersection angle of θ (0° < θ < 180°). [Zhu et Wang, Lab on Chip, 2017]

Cross-flow droplet generation modes

Figure 2 : Images of droplet generation with different modes in cross-flow. (a) Squeezing mode. (b) Dripping mode. (c) Jetting mode. [Zhu et Wang, Lab on Chip, 2017]

Flow focusing

The flow focusing corresponds to the formation of dispersed droplets of a fluid in a continuous stream of other fluid. It exists two variants of geometric microfluidic flow-focusing systems: the simple cross junction and the cross junction followed by a constriction (also called nozzle). In addition, it is possible to distinguish a quasi 2D planar configuration (see Fig. 3 (i) (ii)) and an axisymmetry 3D configuration (see Fig. 3 (iii) (iv)).

Compared to planar flow focusing devices, 3D axisymmetric flow-focusing devices avoid issues such as wetting of channel walls by the dispersed phase, therefore producing monodisperse droplets using higher throughputs.

Then, as for the cross-flow geometry, it is possible to distinghish three different modes : squeezing, dripping and jetting modes (see Fig. 4). The advantage of using flow focusing lies in its simplicity in terms of geometry, hence its many design variations. However, there is not a simple mechanistic model available that can predict droplet size over a wide range of flow conditions. An other well-known problem is the unwanted merging of droplets, which can be prevented by the use of surfactants. However, surfactants can also interfere or inhibit the biochemical reactions.

Flow-focusing designs for droplet generation

Figure 4 : Flow-focusing. (i) Axisymmetric flow-focusing geometry. (ii) Planner flow-focusing geometry. (iii) Microcapillary flow-focusing device. (iv) Microcapillary device combining co-flow and flow-focusing geometries. [Zhu et Wang, Lab on Chip, 2017]

Images of flow-focusing droplet generation

Figure 5 : Images of droplet generation with different modes in flow-focusing. (a) Squeezing mode. (b) Dripping mode. (c) Jetting mode. [Zhu et Wang, Lab on Chip, 2017]

Multichannel dynamic interface

The most classically used geometries in microfluidic droplets are flow-focusing and T junctions. It should be understood that these techniques require increased technical skills and specialized equipment which can be a barrier for laboratories not specialized in microfluidics. Besides, the droplet size can be affected by many factors such as fluid viscosity, interfacial tension, channel size, etc.

Here, a simple active (electrical) technique for generating droplets using the dynamic interfacial shearing driven by a mechanical device (see Fig. 1) is used. Pratically, liquid components converge on the nozzle and generate droplets with the interfacial shear due to the vibration of a multichannel capillary.

 Multichannel dynamic interface

Figure 1 : Scheme of the multichannel dynamic interface. A tapered 3-channel capillary connected with three syringes loading differentcomponents is allowed to vibrate at the oil surface. Because of the interfacial shearing process, the droplets mixed with three distinct components are “printed” into 96-well plate. Droplet components can be precisely controlled by tuning flow rate of discrete channels. [Liao et al, American Chemical Society, 2017]

One of the first advantages is that the device is simply based on a cheap vibrator and handmade tapered multichannel capillary, which is easy to assemble and usable by everyone without any expertise in droplet generation. The other advantage is that the technique exhibits excellent performance in generating uniform droplets with predesigned size and components. Although the manufacturing and assembly are easy, the fact that the microchannels are made by hand can represent a bias in the reproducibility of the device but can also influence the size of the droplets generated by two different devices using the same settings. Moreover, this technique is limited to a small number of biological applications such as bacteria study because the droplet diameter decreases as the capillary number increases, due to increased viscous stresses acting to deform the droplet.

Conclusion

In this review, we saw a very small part of existing geometries and their variations to generate microfluidic droplets. Each of them has its unique characteristics in terms of flow instabilities, droplet size or droplet behaviors. For an effective droplet production with the desired outcome, it is important to have a deep understanding regarding the effects of viscous, inertial and capillary forces. Thus, as the precise dependence of droplet size on the flow parameters depends on the specific geometry considered, it is important to take into account the precise needs and constraints of the desired research application to choose the perfect droplet generation design.

  • Share
  • Tweet
welcome to our blog!
Our team keeps you informed of the latest news at Darwin Microfluidics. We also write some nice reviews and tools to guide you through the vast world of microfluidics!
Categories
  • News
  • Reviews
  • Tutorials
  • Tools
Recent posts
Hardness Shore A vs. Shore D
06 Jul, 2021
Tygon Tubing Hardness Table
06 Jul, 2021
Tygon tubing chemical compatibility comparison chart
05 Jul, 2021
Tags
  • All
  • cell culture
  • microfluidic chip
  • new products

Recently Viewed

Ismatec - Darwin Microfluidics
Elveflow - Darwin Microfluidics
Microfluidic ChipShop - Darwin Microfluidics
Zeiss - Darwin Microfluidics
Harvard Apparatus - Darwin Microfluidics
Cole-Parmer - Darwin Microfluidics
Sign up to our Newsletter

...for latest news in microfluidics.

Darwin Microfluidics
Got questions? Call us! (+33) 189 197 051
Contact info Darwin Microfluidics
172 rue de Charonne
Bâtiment B1, 1er étage
75011 Paris
France
  • Social
Blog
  • News
  • Reviews
  • Tutorials
  • Tools
Information
  • Bank Details
  • General Terms & Conditions
  • Delivery Terms
  • Payment Terms
The Company
  • About us
  • Contact us
  • Terms of Service
  • Refund policy

© 2023 Darwin Microfluidics. All Rights Reserved

  • Payment

Product successfully added to your Shopping Cart

Request a Quote
Proceed to Checkout