Droplet Microfluidic Technology

From organic chemistry, biological applications to the food industry, droplet production is a hot topic in many applications. Alfa Chemistry introduces you to the main droplet production methods, from common batch processing methods to microfluidic technology. We briefly describe the concept of pressure-driven flow-controlled microfluidics for droplet generation.

The droplet-based microfluidics technology is an emerging technology based on the principle of fluid dynamics, which processes fluids accurately and reliably, providing an indispensable tool for minimizing and automated assays.

Droplet Production Methods

Droplet Generation Batch Method

The most common batch method can be performed simply by mixing water and oil in a jar and shaking it thoroughly. Due to instability (Osterwald ripening), the mixture of two immiscible fluids called "emulsions" will disappear over time.

Instability can be avoided by the following methods:

• Adjust the rheological properties of the two phases, such as viscosity.
• Monodisperse droplets that form an emulsion are produced to prevent Ostwald ripening.
• Amphoteric molecules or surfactants are added to one of the two immiscible phases to reduce the interfacial tension between the two phases.

On a bigger scale, a high-shear mixer can be used to mix two immiscible fluids. Due to the lack of control over the resulting droplet size, high shear mixing still causes emulsion instability.

Microfluidic Droplet Production Method

In recent years, microfluidic technology has gradually replaced high-shear mixers for mass production of droplets to produce highly monodisperse droplets and produce stable emulsions for many applications.

Figure.1 Three principle microfluidic geometries are available for droplet production. (Collins D, et al. 2015)

The droplet microfluidic technology is a part of the droplet production method, which can realize: the production and processing of droplets is a microreactor with a single picoliter capacity; high monodisperse droplet generation (CV<2%); biological or chemical reagents Miniaturization of production, processing, and analysis.

To use microfluidics to produce droplets, you need to:

• Mix two immiscible fluids (water-in-oil/oil-in-water).
• Choose suitable surfactants to produce stable droplets or emulsions.
• Choose the appropriate microfluidic chip (flow focusing, co-current, or T-junction) to ensure that the droplet size is correct under laminar flow.
• Determine the flow control system to ensure repeatable experiments and effective control of droplet size and generation frequency.

Why Choose Microfluidics to Make Droplets?

Generally, particles, nanoparticles, and emulsions are formed by batch methods. These methods generate a lot of material and are very simple to use. However, the particles produced are polydisperse and therefore often need to be filtered. High shear stress can also cause problems, eg. with encapsulated payload.

The microfluidic approach has many important advantages:

Control System for Droplet Microfluidics

Usually, syringe pumps are the most commonly used system in microfluidics. Due to its unique performance-enhancing experiments, researchers have recently begun to turn to pressure control systems. Pressure-driven flow control allows an impulse-free flow within a sub-second response time. It consists in using a gas input pressure within a hermetic liquid tank in order to flow liquid from the tank to your microfluidic device.

The pressure controller pressurizes the container containing the sample to be pushed out through the capillary tube. A flow sensor is placed before the chip measures the flow rate and feeds it back to the software, which then adjusts the pressure applied to the liquid tank to maintain a steady flow rate.

Can Your Research Benefit From Droplet-based Microfluidic Technology？

• Droplet-sequencing
• Droplets Encapsulation for Biological Applications
• Droplet Detection and Measurement in Microfluidic Channels

Reference

• Collins D, et al. (2015). "The Poisson Distribution and Beyond: Methods for Microfluidic Droplet Production and Single Cell Encapsulation." Lab Chip. 15: 3439-3459.

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