Shape Fluctuations and Curvature-Driven Mechanics of Heterogeneous Lipid Vesicles*

We investigate heterogeneous vesicles consisting of mixtures of different lipids. We develop single-bead implicit-solvent coarse-grained models based on anisotropic pair potentials to capture vesicle shapes arising from species with different preferred curvatures. We develop theory and methods for mapping our molecular results to continuum mechanics descriptions, useful for analysis of fluctuation spectra to estimate bending elasticities and other mechanical parameters. For mixed lipid species, we find that passive fluctuation spectra are significantly influenced by the formation of small curved segregated domains. We actively probe the vesicle mechanics with compression and narrow-passage transport experiments. When compressed, we find that high-curvature domains arrange circumferentially, leading to a smaller resistance force. When transporting through a narrow passage, we find that mixed vesicles are characterized by much higher variances in passage times. We also find that geometric effects can delay phase-separation in the bulk and promote phase-separation during channel transport, resulting in occasional budding events. Our results may have implications for biological systems, fluidics utilizing vesicles, and other experimental assays.