Water-in-Water Droplets by Passive Microfluidic Flow Focusing

Area of Science:

• Biotechnology
• Microfluidics
• Materials Science

Background:

• Aqueous two-phase systems (ATPS) are crucial for bioseparations and cell encapsulation.
• Generating stable, monodisperse ATPS droplets often requires complex microfluidic setups or external energy inputs.
• Existing methods for low interfacial tension ATPS droplet formation without external perturbations are limited.

Purpose of the Study:

• To develop a simple, passive microfluidic system for generating water-in-water ATPS droplets.
• To investigate the control mechanisms for droplet size and polydispersity.
• To demonstrate the scalability and potential applications of the developed system.

Main Methods:

• Utilized passive flow focusing with weak hydrostatic pressures and liquid-filled pipette tips for fluid delivery.
• Systematically varied interfacial tension, viscosity, and fluid column height to control droplet size.
• Developed a parallel microfluidic system for simultaneous droplet generation and increased production rates.

Main Results:

• Achieved stable ATPS droplet formation under low hydrostatic pressures.
• Demonstrated power-law scaling of droplet size with the ratio of viscous stresses.
• Obtained droplet size coefficients of variation (CV) around 10%, with <1% CV for drops formed near the junction.
• Showcased successful encapsulation of microparticles and cells within the generated droplets.

Conclusions:

• The developed microfluidic system offers a simple and effective method for producing low interfacial tension ATPS droplets without external perturbations.
• The technique allows for precise control over droplet size and high monodispersity, crucial for applications.
• The system is scalable and demonstrates potential for biocompatible cell and drug delivery applications.