Continuous Suspension of Lipids in Oil by the Selective Removal of Chloroform via Microfluidic Membrane Separation

Semi-permeable vesicles produced by microfluidics to tune the phase behaviour of encapsulated macromolecules

Understanding the dynamics of macromolecular assemblies in solution, such as Liquid-Liquid Phase Separation (LLPS), represents technologic and fundamental challenges in many fields. In cell biology, such dynamics are of great interest, because of their involvement in subcellular processes. In our study, we aimed to control the assembly of macromolecules in aqueous semi-permeable vesicles, that we named osmosomes, using microfluidics. We developed a microfluidic chip that allows for producting and trapping Giant Unilamellar Vesicles (GUVs) encapsulating macromolecules. This device also allows for modification of the composition of the inner phase and of the membranes of the trapped GUVs. The vesicles are produced from water-in-oil-in-water (w/o/w) double emulsions in less than 20 min after discarding the oil phase. They are highly monodisperse and their diameter can be modulated between 20 and 110 µm by tuning the flow rates of fluid phases. Their unilamellarity is proofed by two techniques: (1) fluorescence quenching experiments and (2) the insertion of the α-hemolysin membrane protein pore. We demonstrate that the internal pH of osmosomes can be tuned in less than 1 min by controlling solvent exchanges through the α-hemolysin pores. The detailed analysis of the exchange kinetics suggests that the microfluidic chip provides an efficient pore formation due to the physical trapping of vesicles and the constant flow rate. Finally, we show a proof of concept for macromolecular assembly within osmosomes by pH-triggered LLPS of wheat proteins within a few minutes.

Microfluidic tools for lipid production and modification: a review

Microfluidics has great potential as an efficient tool for a large range of applications in industry. The ability of such devices to deal with an extremely small amount of fluid has additional benefits, including superlatively fast and efficient mass and heat transfer. These characteristics of microfluidics have attracted an enormous amount of interest in their use as a novel tool for lipid production and modification. In addition, lipid resources have a close relationship with energy resources, and lipids are an alternative renewable energy source. Here, recent advances in the application of microfluidics for lipid production and modification, especially in the discovery, culturing, harvesting, separating, and monitoring of lipid-producing microorganisms, will be reviewed. Other applications of microfluidics, such as the modification of lipids from microorganisms, will also be discussed. The novel microfluidic tools in this review will be useful in applications to improve lipid production and modification in the future.

The Poisson distribution and beyond: methods for microfluidic droplet production and single cell encapsulation

There is a recognized and growing need for rapid and efficient cell assays, where the size of microfluidic devices lend themselves to the manipulation of cellular populations down to the single cell level. An exceptional way to analyze cells independently is to encapsulate them within aqueous droplets surrounded by an immiscible fluid, so that reagents and reaction products are contained within a controlled microenvironment. Most cell encapsulation work has focused on the development and use of passive methods, where droplets are produced continuously at high rates by pumping fluids from external pressure-driven reservoirs through defined microfluidic geometries. With limited exceptions, the number of cells encapsulated per droplet in these systems is dictated by Poisson statistics, reducing the proportion of droplets that contain the desired number of cells and thus the effective rate at which single cells can be encapsulated. Nevertheless, a number of recently developed actively-controlled droplet production methods present an alternative route to the production of droplets at similar rates and with the potential to improve the efficiency of single-cell encapsulation. In this critical review, we examine both passive and active methods for droplet production and explore how these can be used to deterministically and non-deterministically encapsulate cells.