Elastically confined polar active filaments*

The field of active matter studies materials whose microscopic constituents can consume energy at the particle scale to produce motion. Many biological processes are driven by such internal active components, such as cell migration due to the actin cytoskeleton, where collective motion of active filaments can lead to the cell forming protrusions, and morphogenesis, where topological defects can act as nucleation sites for morphological features. As a minimal model of a cell, we consider a particle-based simulation of an elastic vesicle containing a collection of polar active filaments. The interplay between the internal active stresses and vesicle elasticity leads to a variety of fascinating steady-state behaviors that have not been observed in bulk systems or under rigid confinement, including highly-aligned rings and caps. We discuss simple scaling models that reveal the mechanisms underlying these emergent behaviors.