  The field of active matter studies materials whose microscopic constituents
consume energy at the particle scale to produce motion. Many biological
functions are driven by confinement of active components within a cell,
including cytoplasmic streaming, morphogenesis, and cell migration powered by
the actin cytoskeleton. As a minimal representation of such 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 filament spatiotemporal organizations
that have not been observed in bulk systems or under rigid confinement,
including highly-aligned rings and caps. In turn, these filament assemblies
drive dramatic and tunable transformations of the vesicle shape and its
dynamics. We present simple scaling models that reveal the mechanisms
underlying these emergent behaviors.
