In Silico Conformational Dynamics and Mechanics of Soft Vesicle Enclosing Self-Propelled Particles*

Using coarse-grained molecular dynamics simulations, we explore the conformational dynamics and mechanics of soft vesicles containing numerous self-propelled particles (SPPs). These SPPs are characterized as polarized, disjoint ring polymers. We systematically vary parameters such as the SPP packing fraction (ρ), motility force (f), vesicle bending rigidity (κ), and one-dimensional compressibility  (ς). At high packing fractions combined with high f, distinct collective motion patterns of SPPs emerge within the vesicle, depending on κ and ς values. For low κ and ς, the SPPs demonstrate dominant collective vortical motion, leading the vesicle to be in a consistently rotating state with minimal motility. In contrast, high κ and ς values shift the collective SPP behavior from vortical to pronounced ballistic motion, giving rise to a highly active elongated vesicle with its polarity steered by SPP activity. This study offers a simple computational model that helps us understand the intricate dynamics of vesicles laden with active particles. Such insights hold a potential in advancing our understanding of both engineered systems with dry active particles and natural cellular mechanisms in quasi-two dimensions.