Passive droplet generation in aqueous two-phase systems with a variable-width microchannel

Area of Science:

• Microfluidics
• Biophysics
• Materials Science

Background:

• Aqueous two-phase systems (ATPS) are crucial for cell separation and biochemical analysis.
• Generating stable droplets in ATPS, especially with low solute concentrations, presents significant challenges.
• Existing microfluidic droplet generation methods often lack control over droplet properties for specific applications.

Purpose of the Study:

• To develop a passive, fracture-based microfluidic method for droplet generation in ATPS.
• To investigate the influence of microchannel geometry and operating parameters on droplet characteristics.
• To demonstrate the utility of this method for generating droplets relevant to live cell applications.

Main Methods:

• Utilized a fracture-based variable microchannel with adjustable inlet width (1-10 μm) via mechanical strain.
• Generated a dextran-rich (DEX) phase jet within a polyethylene-glycol (PEG)-rich phase.
• Analyzed droplet properties including production rate, diameter, and variance under varying pressures and concentrations.

Main Results:

• Achieved spontaneous formation of DEX droplets with ultralow surface tension (12 μN m-1).
• Demonstrated droplet production rates of 2-20 droplets/s with diameters ranging from 10-100 μm.
• Showcased control over droplet properties by manipulating inlet channel width and operating conditions.

Conclusions:

• The developed method offers a simple, robust, and tunable approach for passive droplet generation in ATPS.
• This technique significantly enhances droplet generation capabilities in microfluidics, particularly for ATPS with low solute concentrations.
• The findings are highly relevant for applications involving live cells and biochemical assays.