Tuning the microstructure of phospholipid monolayers using substrate curvature

Two-dimensional monolayers and bilayers of phospholipids exhibit a heterogeneous microstructure, which is essential for fluidity, mechanical stability, and spatial localization of proteins, cholesterol, and signaling molecules. There is a growing body of evidence that lipid morphology is influenced by the curvature of the underlying template. Although this geometric dependence remains poorly understood, it becomes extremely relevant to the study of monolayers (e.g., in lung alveoli and microemulsions) and bilayers (in cells, organelles, and vesicles) with radii of curvature on the order of 10-100 microns. In this work, I will discuss how continuum-level theory can predict the effect of curvature on the phase behavior of lipid monolayers, using planar and spherical geometries as model templates. First, I will demonstrate that curvature decreases the expected radius of condensed domains due to the attenuation of dipolar repulsions. Second, I will show that curvature stabilizes circular domains (“droplets”) from elliptic distortions into elongated structures (“stripes”). The transition between these states is determined by the substrate curvature and condensed-phase area fraction, which parametrize the phase space of lipid morphologies on curved templates.