Shape fluctuations of fluidized vesicles driven by dilute active nematics.*

Motivated by recent experiments on the microtubule-kinesin active nematics confined in vesicles, we study a microscopic particle-based model of semiflexible polymers with nematic activity confined in fluid vesicles. Using Brownian dynamics simulations, we characterize the emergent behaviors as a function of control parameters including filament length, vesicle size, and rigidities of the filaments and vesicles. We find that the interplay between internal active stresses from the enclosed filaments, the elasticity and fluidity of the confining vesicle leads to novel emergent filament organizations not seen in other active matter systems, as well as interesting transformations of the vesicle shapes and dynamics. In particular, the resulting vesicle shape fluctuations exhibit clear non-equilibrium signatures. We compare predicted vesicle shape fluctuation correlation functions with those measured in experiments. Moreover, in the simulations we find correlations between vesicle fluctuations and the spatiotemporal organization of enclosed filaments, which may enable inferring filament organizations in the experimental results. This study elucidates physical mechanisms that underlie diverse cellular biophysical phenomena that involve membrane shape transformations.