The combination of block copolymers and phospholipids to form giant hybrid unilamellar vesicles (GHUVs) does not systematically lead to “intermediate” membrane properties

Abstract

In this work, the elasticity under stretching as well as the fluidity of Giant Hybrid Unilamellar Vesicles (GHUV) has been studied. The membrane structuration of these GHUVs has already been studied at the micro and nanoscale in a previous study of the team. These GHUVs were obtained by the association of a fluid phospholipid (POPC) and a triblock copolymer, poly(ethyleneoxide)-b-poly(dimethylsiloxane)-b-poly(ethyleneoxide). Although the architecture of triblock copolymers can facilitate vesicle formation, they have been scarcely used to generate GHUVs. We show, through micropipette aspiration and FRAP experiments, that the incorporation of a low amount of lipids in the polymer membrane leads to a significant loss of the toughness of the vesicle and subtle modification of the lateral diffusion of polymer chains. We discuss the results within the framework of the conformation of the triblock copolymer chain in the membrane and in the presence of lipid nanodomains.

Large and Giant Unilamellar Vesicle(s) Obtained by Self-Assembly of Poly(dimethylsiloxane)-b-poly(ethylene oxide) Diblock Copolymers, Membrane Properties and Preliminary Investigation of Their Ability to Form Hybrid Polymer/Lipid Vesicles

“…Area compressibility moduli range from 113 to 121 mN·m −1 . They are slightly higher than those obtained for membrane of triblock copolymers PEO-b-PDMS-b-PEO (80-90 mN·m −1 ) [15] and grafted copolymer PDMS-g-PEO (~95 mN·m −1 ) [30,41]. In the literature, it is commonly considered that the amplitude of the stretching modulus is linked to the interfacial tension [31,42] (i.e., dictated by chemical nature of the monomers and solvent alone) and independent of molar masses.…”

“…Interestingly, the membrane resulting from the self-assembly of these diblock copolymers presents higher lysis strain than those obtained from triblock copolymer of similar membrane thickness [15], and slightly higher stretching modulus. Furthermore, beyond an area strain of 10%, the membrane tension evolves nonlinearly with area strain, as has already been observed for polymersomes obtained with PBut-b-PEO copolymers but with high molar mass of hydrophobic block (>7000 g·mol −1 ) [38].…”

“…The toughness of the GUV seems to evolve with membrane thickness as a power law~d 5.8 (Figure 7). This make these diblock copolymers far more interesting than triblock copolymers PEO-b-PDMS-b-PEO, which displays relatively low lysis strain (<8% for membrane thickness around 8 nm) [15,43] for the development of hybrid polymer/lipid vesicles.…”

“…Thus far, relatively little information is available about the structure, chemical nature, and molar mass of copolymers that could mix ideally with phospholipids. Most commonly, poly(butadiene) [3][4][5][6][7][8][9][10][11][12] and poly(dimethylsiloxane) [13][14][15][16][17][18][19][20] have been used as hydrophobic block, while studies with poly(isobutene) [21][22][23], poly(caprolactone) [24,25], poly(isoprene) [26], and poly(laurylacrylate) [27] have also been reported. Poly(ethylene oxide) is by far the most used hydrophilic block, although few studies report the use of hydrophilic thermo-responsive blocks such as poly(2-isopropyl-2-oxazoline) [28] and poly(ethylene glycoldiacrylate) [27].…”

“…In the only study describing the association of triblock copolymer and lipid in a fluid state (poly(ethylene oxide)-b-poly(dimethylsiloxane)-b-poly(ethylene oxide) with POPC), it has been reported that the resulting hybrid vesicles were even more fragile than pure liposomes, although membrane thickness of the polymersomes and lipid/polymer fraction were comparable to those of PBut-PEO/POPC. It has been surmised that mixture of hairpin and stretch conformations of polymer chains in the membrane could make obtaining stable edifices with lipids difficult [15].…”