A Microfluidic Platform to Produce and Manipulate Liposomes - Towards Synthetic Cells on Chip

Abstract

Liposomes are versatile supramolecular assemblies that are widely used in basic as well as applied sciences. Importantly, they mimic the semi-permeable lipid-bilayer boundary of living cells, and thus lie at the very heart of creating synthetic cells. Using liposomes as the basic architectural element and a controlled microfluidic environment, we wish to establish a continuous growth-division cycle of liposomes.We have developed a new and robust microfluidic technique to form unilamellar, cell-sized (5-20 μm), and monodisperse liposomes with an excellent encapsulation efficiency. Named octanol-assisted liposome assembly (OLA), our method involves a bubble-blowing process where an inner aqueous phase and a biocompatible 1-octanol phase containing lipids are simultaneously focused and pinched-off by an outer aqueous phase to form a double-emulsion droplet. This double-emulsion droplet quickly develops into an intermediate complex of a liposome connected to a 1-octanol pocket, and owing to interfacial energy minimization, the pocket spontaneously separates within a few minutes, leaving behind a fully functional liposome. We show the unilamellarity of the OLA-based liposomes by inserting functional α-hemolysin pores in the membranes. OLA is robust to physiological salt concentrations and variations in the bilayer composition, rendering it a very versatile high-throughput technique. It also circumvents the common problems such as remnants of unwanted organic solvents in the lipid bilayer and the time-consuming solvent-extraction associated with existing methods.In order to gain further control and increase the stability of the liposomes, we incorporate pneumatic valves, decoupling the production phase from the manipulation phase, and use dielectrophoresis to separate the liposomes from 1-octanol droplets. Future plans are aimed at exploring the division of liposomes using a combination of physical and biological approaches. Establishing on-chip growth-division cycle of liposomes would present a breakthrough towards synthetic cells.