Hybrid polymer/lipid vesicles: Influence of polymer architecture and molar mass on line tension

Abstract

Hybrid polymer/lipid vesicles are self-assembled structures that have been the subject of an increasing number of studies in recent years. They are particularly promising tools in the development of cell membrane models because they offer the possibility to fine-tune their membrane structure by adjusting the distribution of components (presence or absence of "raft-like" lipid domains), which is of prime importance to control their membrane properties. Line tension in multiphase membranes is known to be a key parameter on membrane structuration, but remains unexplored, either experimentally or by computer modeling for hybrid polymer/lipid vesicles. In this study, we were able to measure the line tension on different budded hybrid vesicles, using a micropipette aspiration technique, and show the influence of the molar mass and the architecture of block copolymers on line tension and its consequences for membrane structuration.

Graphical abstract

Figure 1

Example of line tension measurement on GHUVs made from PDMS₂₃-b-PEO₁₃/POPC at different suction pressure (values indicated in the top right of each picture). Lipid phases are tagged in red while polymer phases are tagged in green.

Figure 2

Schematic view of the hybrid polymer/lipid membrane with a lateral phase separation.

Figure 3

Average measurements (black circles) and standard deviation (colored areas) of the membrane tension as a function of areal strain for the polymersomes obtained from PDMS₂₃-b-PEO₁₃ (A), PDMS₂₇-b-PEO₁₇, (B) and PEO₈-b-PDMS₂₂-b-PEO₈ (C). Bending moduli are extracted from the slope of the curve (linear regression) in the low-tension regime.

Figure 4

Example of the evolution of the suction pressure as a function of the geometrical parameter (1/A) for the hybrid system POPC/PEO₈-b-PDMS₂₂-b-PEO₈. The red part corresponds with a linear evolution whose slope allow to determine the line tension.

Figure 5

Left) Scatter plot of measurements obtained for PDMS₂₃-b-PEO₁₃/POPC (red dots), PDMS₂₇-b-PEO₁₇/POPC (blue dots) and PEO₈-b-PDMS₂₂-b-PEO₈/POPC (green dots) (data: mean (value indicated) ± SE). (Right) Evolution of the line tension as a function of the hydrophobic length mismatch (data: mean ± SE; Brown-Forsythe and Welch test; Games-Howell's multiple comparisons post-test, p values are indicated). The red dotted line in the shaded area corresponds with the thickness mismatch for other copolymers, for which hybrid vesicles were obtained without lateral phase separation whatever the lipid composition.