Microfluidic Production of Double Emulsions: Designer Microcapsules, Dropmaker Wettability Patterning, and Parallelization

Abstract

Microfluidics enables the production of complex emulsions drops with high degree of uniformity and control over structure. These complex emulsion drops can be used as templates to form tailored materials with dimensions from tens to hundreds of microns which can be utilized for a diverse array of applications, including encapsulation and controlled release of cargo. This work explores the use of microfluidic technologies for the production of double emulsions and microcapsules. We develop several novel approaches and systems for precisely patterning the wettability of dropmaker channels and parallelization to achieve increases in drop production throughput. We begin with an introduction on the use of microfluidic devices for double emulsion generation and provide an overview on the current limitations of the technology. The first portion of the work focuses on the scalable generation of double emulsions using thermoplastic microfluidic devices. We start by describing the development of double emulsion dropmakers with a multilayer channel geometry that enables robust parallelization of dropmakers. Next, we detail work on a sequential direct micromachining-based fabrication approach that enables spatially controlled modification of microfluidic channels, resulting in precisely segregated channel surface wettability. Finally, we focus on the development of a conformal masking approach for spatially patterning the wettability of dropmaker channels. The masking approach is applied for dropmaker parallelization to demonstrate high-throughput production of monodisperse double emulsions. The second portion of the work moves toward soft lithography-based approaches for fabricating scalable microfluidic platforms for the production of double emulsions. We begin by discussing two-step systems for producing complex emulsion drops, and then delve into the development of a soft lithography-based millifluidic system for producing monodisperse double emulsions and capsules with sizes close to 1 mm. Finally, we describe work on spatially patterning the wettability of double emulsion dropmakers using surfactants. The third portion of the work focuses on the production of designer microcapsules using microfluidic technologies. In particular, we describe work on the production of stimuli-responsive hydrogel microcapsules with pH-controlled permeability properties.