Block Copolymer Vesicle Permeability Measured by Osmotic Swelling and Shrinking

Abstract

Vesicle response to osmotic shock provides insight into membrane permeability, a highly relevant value for applications ranging from nanoreactor experimentation to drug delivery. The osmotic shock approach has been employed extensively to elucidate the properties of phospholipid vesicles (liposomes) and of varieties of polymer vesicles (polymersomes). This study seeks to compare the membrane response for two varieties of polymersomes, a comb-type siloxane surfactant, poly(dimethylsiloxane)-g-poly(ethylene oxide) (PDMS-g-PEO), and a diblock copolymer, polybutadiene-b-poly(ethylene oxide) (PBut-b-PEO). Despite similar molecular weights and the same hydrophilic block (PEO), the two copolymers possess different hydrophobic blocks (PBut and PDMS) and corresponding glass transition temperatures (-31 and -123 °C, respectively). Dramatic variations in membrane response are observed during exposure to osmotic pressure differences, and values for polymer membrane permeability to water are extracted. We propose an explanation for the observed phenomena based on the respective properties of the PBut-b-PEO and PDMS-g-PEO membranes in terms of cohesion, thickness, and fluidity.

Modulation of phase separation at the micron scale and nanoscale in giant polymer/lipid hybrid unilamellar vesicles (GHUVs)

“…Amphiphilic graft copolymer PDMS 26 -g-(PEO 12 ) 2 was a gift from Dow Corning Inc. (#5329) and thereafter denoted DOW. The characterizations of this copolymer were performed in the lab in a previous study 28 , all the results were in agreement with data given by the manufacturer and data available in literature 29,30 This copolymer form vesicles with a membrane thickness close to 5 nm. Fluorescein-labelled graft copolymer (PDMS 26 -g-(PEO 12 ) 2 -FITC) was prepared as previously described.…”

“…It has been shown in literature that cooling rate has an effect on the membrane tension as it induces a thermal contraction of both membrane and water, the contraction of membrane being faster than the aqueous core of the vesicle, inducing membrane stress which can goes through a maximum. 28 Indeed at high cooling rate, the rapid contraction of the membrane compared to the aqueous compartment abruptly reduces the surface-to-volume ratio and thus induces lateral tension in the membrane that can go above its lysis tension, inducing rupture and reseal phenomena during which water escapes from the vesicle, therefore relaxing tension. At low cooling rate, the membrane tension is continuously relaxed by natural diffusion of water through the membrane.…”

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

“…Amphiphilic graft copolymer PDMS 26 -g-(PEO 12 ) 2 was a gift from Dow Corning Inc. (#5329) and thereafter denoted DOW. The characterization of this copolymer was performed in the lab in a previous study 34 , and all the results were in agreement with data given by the manufacturer and data available in literature 35,36 This copolymer forms vesicles with a membrane thickness close to 5 nm. We used this copolymer to validate our MPA procedure, as GUVs of this copolymer have already been studied by MPA and their stretching elasticity is well established.…”

Constraining Polymers into β-Turns: Miscibility and Phase Segregation Effects in Lipid Monolayers

“…Being superior in mechanical performance, with significantly enhanced bending moduli in comparison to lipid-bilayer membranes [2], they also display drawbacks, such as a reduced membrane mobility, a large thickness, or significantly reduced transport properties across the membrane [3,4]. In order to merge the advantages of polymersomes with those of lipid bilayer membranes, mixed-systems between those two components have gained significant attention during the past years, placing the principles of formation, stability, and most of all miscibility of these two systems into the limelight [5][6][7][8].…”