DROPLETS GENERATION & MANIPULATION
Droplets-based microfluidics consists in manipulating discrete volumes of fluids in immiscible phase, such as water droplets in oil.
The generation and manipulation of droplets through microfluidics offer tremendous advantages: better control over small volumes of fluid, enhanced mixing, high throughput experiments.
Droplets generation has a large scale of applications, such as:
Emulsions and foams, Nanoparticles fabrication, Cell Encapsulation, Drug delivery ….
Microfluidic droplets generation systems are used to create monodispersed water or oil droplets in an immiscible phase. In passive droplets production methods, the key principle is to use at least two streams of immiscible fluids and to create a shear force on one of the phases in order to break the stream in discrete droplets.
They are two main motivations for creating microfluidic droplets. The first one is to generate droplets with a very high monodispersity, and microfluidic offers very consistent size of droplets, contrary to conventional batch methods for emulsion productions. Material science applications, such as food or pharmaceutical industries, greatly benefit from these new microfluidic techniques.
The second one is to compartmentalize a given sample. Microfluidic droplets are then a way to manipulate very small and precise volumes of samples, but also to realize high throughput experiments, as each droplet become a distinct microreactor. Moreover, droplets are a way to enhance mixing of chemical and overcome one of the most fundamental issue of single phase microfluidics.
The applications for microfluidic droplets include:
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The 2 mains methods:
There are different methods to produce droplets and we present here the two most used methods for digital microfluidics. These methods use two immiscible phases (usually water and oil) and specific chip designs allowing to break one of the streams in discrete droplets.
In these two methods, a very accurate flow control system is necessary to obtain a precise control over the droplets parameters (size and frequency).
For more detailed protocoles, please check our application note.
Surface wettability: This is a crucial parameter to avoid droplets sticking to the chip’s walls. For water-in-oil droplets, the surface must be hydrophobic. For oil-in-water droplets, the surface must be hydrophilic.
Surfactant: The use of surfactant helps prevent droplets coalition.
Flow focusing method
In the flow focusing method, the middle phase is squeezed between two streams of the continuous phase.
T junction method
In this configuration, the two phases are injected (generally with a pressure controller) in two orthogonal channels. The droplet formation occurs at the intersection of the two channels.
You will find hereafter a short list of microfluidic publications about droplets. If you wish to add a specific publication to this list, please contact us!
- Baroud, C. N., Gallaire, F., & Dangla, R. (2010). Dynamics of microfluidic droplets. Lab on a Chip, 10(16), 2032-2045.
- Teh, S. Y., Lin, R., Hung, L. H., & Lee, A. P. (2008). Droplet microfluidics. Lab on a Chip, 8(2), 198-220.
- I Solvas, X. (2011). Droplet microfluidics: recent developments and future applications. Chemical Communications, 47(7), 1936-1942.
- Weibel, D. B., & Whitesides, G. M. (2006). Applications of microfluidics in chemical biology. Current opinion in chemical biology, 10(6), 584-591.
- Song, H., Chen, D. L., & Ismagilov, R. F. (2006). Reactions in droplets in microfluidic channels. Angewandte chemie international edition, 45(44), 7336-7356.
- Brouzes, E., Medkova, M., Savenelli, N., Marran, D., Twardowski, M., Hutchison, J. B., … & Samuels, M. L. (2009). Droplet microfluidic technology for single-cell high-throughput screening. Proceedings of the National Academy of Sciences, 106(34), 14195-14200.