Hybrid Emulsions for the Efficient Formation of Giant Unilamellar Vesicles

Droplet-templated production of giant unilamellar vesicles (GUVs) (mediated by either nanoparticles or surfactants) offers an emergent platform for the bottom-up assembly of synthetic cells. Currently, these techniques suffer from inherent efficacy and scalability challenges, which hinder the possibility to generate biologically relevant vesicles (i.e., supporting transmembrane proteins) for therapeutic applications. Here, we report on a novel methodology that harnesses synergistic effects of hybrid emulsions (i.e., combining fluorosurfactants with fluorinated silica nanoparticles, FSiNPs) to modulate the interfacial stability of the generated emulsions, allowing for a more nuanced and efficient production of GUVs via the droplet-templated technique. Droplets formed with FSiNPs in combination with three structurally different copolymeric fluorosurfactants (a monoblock, a diblock, and a triblock) display a diversity of effects, some of which synergize with the processes of GUV formation and release. The monoblock Krytox-FSH surfactant (consisting of a carboxylic hydrophilic group linked to a perfluoropolyether moiety, PFPE) appears to adsorb on the surface of FSiNPs, enhancing emulsion stability and hindering GUV release. The previously reported diblock surfactant FSL-PEGMMA360 competitively excludes FSiNPs from the interface, preventing GUV formation altogether. Intriguingly, the triblock surfactant RAN-008 (PEG600-PFPE2) displays a synergistic effect with FSiNPs, which permits GUV assembly while facilitating GUV release. Mechanistic studies using calcein release from GUV-precursor liposomes and fluorescence lifetime imaging microscopy-Förster resonance energy transfer (FLIM-FRET) suggest that this effect may arise from a moderate steric hindrance role of RAN-008 against FSiNPs, which weakens the affinity of the newly formed GUVs for the FSiNPs stabilized at the droplet interface. We further demonstrate that this method is more suitable for preparing GUVs incorporating transmembrane proteins than previously reported droplet-templated techniques. Our results indicate that subtle changes in the interfacial structure of complex amphiphilic systems can drastically impact emulsion stability and their interactions with the proteolipidic components of the dispersed phase, potentially providing optimal conditions for droplet-templated GUV formation.