Flexible filaments in vesicles with reduced volume: Anisotropic confinement and morphological response

Abstract

The mechanical interplay between cell membranes and enclosed filaments is central to various cellular activities, particularly cellular morphogenesis. Here, we present a theoretical study of filament loop-induced shape transformations in vesicles with varying reduced volumes, emphasizing the coupling among filament elasticity, membrane deformability, and anisotropic confinement. We identify a range of morphological transitions—including filament buckling and reorientation, prolate-to-oblate vesicle shape changes, and complex symmetry breaking—governed by relative filament stiffness, length, and vesicle volume. Morphological phase diagrams are constructed, and energy analysis reveals the underlying mechanisms of shape transformations. We further characterize the evolution of membrane tension and examine the packing behavior of inhomogeneous filament loops. The results are complemented by a conceptually driven discussion of how anisotropic confinement and filament–vesicle coupling shape morphogenetic behavior. Our findings provide physical insight into filament–vesicle mechanics, with implications for cell shaping, cytoskeletal organization, and the design of filament-based artificial cells.