Microfluidic production of multiple emulsions and functional microcapsules

Abstract

Recent advances in microfluidics have enabled the controlled production of multiple-emulsion drops with onion-like topology. The multiple-emulsion drops possess an intrinsic core-shell geometry, which makes them useful as templates to create microcapsules with a solid membrane. High flexibility in the selection of materials and hierarchical order, achieved by microfluidic technologies, has provided versatility in the membrane properties and microcapsule functions. The microcapsules are now designed not just for storage and release of encapsulants but for sensing microenvironments, developing structural colours, and many other uses. This article reviews the current state of the art in the microfluidic-based production of multiple-emulsion drops and functional microcapsules. The three main sections of this paper discuss distinct microfluidic techniques developed for the generation of multiple emulsions, four representative methods used for solid membrane formation, and various applications of functional microcapsules. Finally, we outline the current limitations and future perspectives of microfluidics and microcapsules.

The Horizon of the Emulsion Particulate Strategy: Engineering Hollow Particles for Biomedical Applications

“…[13] However, scalable microfluidic productions remained a remarkable challenge. [14] To address this, intrinsic emulsion particulate strategy was employed for facile and scalable production of hollow structures. [15] Through harnessing phase inversion, intrinsic emulsion particlization exploited the destabilizations of the coarse emulsions to encapsulate the external continuous phase into the droplets, which constituted double emulsion in single step.…”

“…For solvent evaporation-based method, the middle phases were normally the volatile solvent, which contained polymers or lipids. At the local area, continual removal of ethanol endowed the growth, mixing and coalescence of the nucleation to form a triple emulsion (Figure 4c, [5][6][7][8]. The diffusion of the volatile solvent caused the interconnected porous structures, whereas, rapid solvent evaporation contributed to the hollow structures without pores.…”

“…As most widely used approaches, templateguided procedures deposit precursors for core-shell structures on the templates (e.g., silica particles or polymeric latex colloids), which are subsequently sacrificed by selective etching. [5] These approaches avoided the involvement of toxic etchants or pore-forming agents, and, to some extent, improved the biosafety profile. However, the inevitable etching procedures are expensive and time consuming, which may also jeopardize the structure and activity of the encapsulated biomolecules.…”

Biopolymer Microparticles Prepared by Microfluidics for Biomedical Applications

“…One of the most promising approaches to meet the several requirements for biomedical applications is to use droplet microfluidics which enables the generation of uniform MPs with well controlled composition and geometrical features by precisely manipulating multiphasic flows at the submillimeter scale . The microfluidics technology features a mild processing condition without a significant energy input, unlike a high‐shear or high‐pressure homogenization, which is particularly attractive for the fabrication of biopolymer MPs to safely encapsulate biomolecules or cells, while maintaining the bioactivities of biopolymer .…”

Smart Microcapsules with Molecular Polarity‐ and Temperature‐Dependent Permeability

“…Recent advances in microfluidic technology have enabled the production of the double‐emulsion drop, or drops‐in‐drop, in a highly controlled manner . As the double‐emulsion drops have a core–shell configuration, they have served as a flexible template to design functional microcapsules.…”