Active microdroplet merging by hydrodynamic flow control using a pneumatic actuator-assisted pillar structure

Abstract

This paper describes a microdroplet merging device that can actively control the merging of various droplets under a wide range of flow conditions, using a simple structure. The microdroplets were trapped and merged in a wide chamber divided by pillars, and their behavior was controlled by two horizontal pneumatic microactuators. Hydrodynamic flow control by the actuation was evaluated numerically, and the trapping and merging of droplets were achieved experimentally and controlled via pressure applied to the microactuators. Furthermore, two independently generated droplets were merged under four different modes, ranging from no merging to four-droplet merging, with different ratios and volumes. The pneumatic actuators allowed not only the control of the number of merged droplets, but also a wide range of applied droplet volumes. The device was fabricated simply using a single-layer PDMS (polydimethylsiloxane) structure, and the continuous merging performance operated using only hydrodynamic flow control without any surfactant. Finally, chemical synthesis of a metal complex was performed by the droplet merging method. Crystallization of the complex was visualized in real time, and the synthesis was verified by ultraviolet-visible spectroscopy.

Advances in Microfluidics Applied to Single Cell Operation

“…Yoon took advantage of the elasticity of PDMS to make two valves structure. By controlling the valves, integration of the different number of droplets was achieved . In respect of active fusion, new techniques including electric fusion, optical trapping, LED (light‐emitting diode), magnetic induced droplet fusion were conducted.…”

Synthesis of an azo-Mn(ii) complex with mild pH control using a microfluidic device

“…20 We have previously established the synthesis of metal complexes and protein-metal complexes using microuidic devices. 21,22 The synthesis of the metal complexes using the microuidic device required a shorter reaction time and no temperature or atmospheric control. 23,24 Furthermore, the conventional synthesis of azo compounds requires harsh pH adjustments using high concentrations of hydrochloric acid and sodium hydroxide.…”

Droplet Merging on a Lab-on-a-Chip Platform by Uniform Magnetic Fields

“…In previous reports, various strategies were utilized to merge droplets e.g., hydrodynamic flow focusing36, surface acoustic waves37, dielectrophoresis38, surfactant-hydrodynamic flow focusing39, droplet velocity-lipid concentration18, electrorheological fluids40, cavitation bubble41, electro-coalescence42 and liquid phase flow43. Most of the above strategies require one or more of the following: direct contact with the liquid, complex microfabrication techniques, changes in the channel geometry, or changes in the flow rates.…”