An asymmetric flow-focusing droplet generator promotes rapid mixing of reagents

I. V. Kukhtevich,A. S. Bukatin,N. A. Filatov,K. I. Belousov,A. A. Evstrapov,V. Kantsler

doi:10.1038/s41598-021-88174-y

Abstract

Nowadays droplet microfluidics is widely used to perform high throughput assays and for the synthesis of micro- and nanoparticles. These applications usually require packaging several reagents into droplets and their mixing to start a biochemical reaction. For rapid mixing microfluidic devices usually require additional functional elements that make their designs more complex. Here we perform a series of 2D numerical simulations, followed by experimental studies, and introduce a novel asymmetric flow-focusing droplet generator, which enhances mixing during droplet formation due to a 2D or 3D asymmetric vortex, located in the droplet formation area of the microfluidic device. Our results suggest that 2D numerical simulations can be used for qualitative analysis of two-phase flows and droplet generation process in quasi-two-dimensional devices, while the relative simplicity of such simulations allows them to be easily applied to fairly complicated microfluidic geometries. Mixing inside droplets formed in the asymmetric generator occurs up to six times faster than in a conventional symmetric one. The best mixing efficiency is achieved in a specific range of droplet volumes, which can be changed by scaling the geometry of the device. Thus, the droplet generator suggested here can significantly simplify designs of microfluidic devices because it enables both the droplet formation and fast mixing of the reagents within droplets. Moreover, it can be used to precisely estimate reaction kinetics.

Highlights

Nowadays droplet microfluidics is widely used to perform high throughput assays and for the synthesis of micro- and nanoparticles
To figure out how the symmetry of the channels influence on the fluids flows and reagents distribution in droplets, we considered an asymmetric flow-focusing microfluidic device with side channels arranged at 45° and 135° to the central channel (Fig. 1a), as well as a symmetric device with side channels arranged at 45° to the central channel (Fig. 1b)
Numerically simulated, and experimentally characterized a novel asymmetric design of flowfocusing droplet generator. This design enables the formation of a single asymmetric recirculation vortex in the dispersed phase during the droplet formation stage, which leads to an improvement in mixing speed

Summary

Introduction

Nowadays droplet microfluidics is widely used to perform high throughput assays and for the synthesis of micro- and nanoparticles These applications usually require packaging several reagents into droplets and their mixing to start a biochemical reaction. In the past decade droplet microfluidics has been successfully applied to molecular diagnostics for performing highly sensitive assays such as droplet digital polymerase chain reaction (ddPCR)[1], loop-mediated isothermal amplification (LAMP)[2], single-cell genome analysis[3,4,5] and for detecting and screening enzymes activity[6] This technique found a great application in chemical s yntheses[7], especially for syntheses of micro- and nanoparticles with specific requirements[8,9]. While it is challenging to reach high mixing efficiency in passive mixers, active mixers allow to mix reaction components more efficiently but consume energy, and overall device design is more complicated

Methods

Results

Conclusion