Beating Poisson stochastic particle encapsulation in flow-focusing microfluidic devices using viscoelastic liquids

TL;DR

This paper demonstrates a method to surpass the Poisson limit in microfluidic particle encapsulation by using viscoelastic liquids to synchronize particle trains with droplet formation, achieving up to twice the efficiency of traditional stochastic methods.

Contribution

The study introduces a novel approach leveraging viscoelastic liquids to enhance encapsulation efficiency and provides a simplified design expression for microfluidic systems.

Findings

Encapsulation efficiency up to 2 times higher than Poisson limit.

First experimental evidence of viscoelastic co-encapsulation from different streams.

Development of a simplified design expression for system optimization.

Abstract

The encapsulation and co-encapsulation of particles in microfluidic flows is essential in applications related to single-cell analysis and material synthesis. However, the whole encapsulation process is stochastic in nature, and its efficiency is limited by the so-called Poisson limit. We here demonstrate particle encapsulation and co-encapsulation in microfluidic devices having flow-focusing geometries with efficiency up to 2-folds larger than the stochastic limit imposed by the Poisson statistics. To this aim, we exploited the recently observed phenomenon of particle train formation in viscoelastic liquids, so that particles could approach the encapsulation area with a constant frequency that was subsequently synchronised to the constant frequency of droplet formation. We also developed a simplified expression based on the experimental results that can guide optimal design of the microfluidic encapsulation system. Finally, we report the first experimental evidence of viscoelastic co-encapsulation of particles coming from different streams.