Packing of flexible nanofibers in vesicles

Cellular packing of flexible nanofibers, including natural cytoskeletal microtubules, actin filaments, synthetic nanotubes and nanowires, is of fundamental interest to the understanding of a wide range of cell activities, including cell shape control, cell movement, cell division, and nano-cytotoxicity. Here, we perform molecular dynamics simulations and theoretical analysis to elucidate how the geometrical and mechanical properties of a flexible nanofiber influence its encapsulation within a lipid vesicle. Our analysis indicates that the packing morphology depends on the length and stiffness of the nanofiber, the initial configuration of the nanofiber–vesicle system and the pressure difference across the vesicle membrane. We establish a packing phase diagram based on three distinct vesicle morphologies in equilibrium, including a non-axisymmetric dumpling-shaped vesicle with a strongly curved nanofiber, a cherry-shaped vesicle with a tubular membrane protrusion enclosing a significant portion of the nanofiber, and an axisymmetric lemon-shaped vesicle with a pair of protruding tips induced by the encapsulated nanofiber.