Filamentous Active Matter: Band Formation, Bending, Buckling, and\n Defects

Abstract

Motor proteins drive persistent motion and self-organisation of cytoskeletal\nfilaments. However, state-of-the-art microscopy techniques and continuum\nmodelling approaches focus on large length and time scales. Here, we perform\ncomponent-based computer simulations of polar filaments and molecular motors\nlinking microscopic interactions and activity to self-organisation and dynamics\nfrom the two-filament level up to the mesoscopic domain level. Dynamic filament\ncrosslinking and sliding, and excluded-volume interactions promote formation of\nbundles at small densities, and of active polar nematics at high densities. A\nbuckling-type instability sets the size of polar domains and the density of\ntopological defects. We predict a universal scaling of the active diffusion\ncoefficient and the domain size with activity, and its dependence on parameters\nlike motor concentration and filament persistence length. Our results provide a\nmicroscopic understanding of cytoplasmic streaming in cells and help to develop\ndesign strategies for novel engineered active materials.\n