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

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 in microfluidic devices having flow-focusing geometries with efficiency up to 2-fold 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.

Automated summary

The encapsulation efficiency of particles in microfluidic devices can be improved by exploiting the phenomenon of particle train formation in viscoelastic liquids, allowing particles to approach the encapsulation area with a constant frequency synchronized to droplet formation. A simplified expression based on experimental results was developed to guide optimal design of microfluidic encapsulation systems. Additionally, experimental evidence of viscoelastic co-encapsulation of particles from different streams was reported for the first time.