Motility Induced Phase Separation of deformable cells

Unlike passive systems, which require attractive interactions to phase separate, active systems with purely repulsive interactions can phase separate via a process called motility-induced phase separation (MIPS). There has been much interest in how particle properties like shape and interaction softness, as well as system properties like polydispersity and cell-division affect MIPS. Much previous work, however, has focused on rigid particles, even though the cells that make up biological systems can significantly deform when closely packed. Using a multi-phase field model, we examine how particle deformability, which is a proxy for cell stiffness, affects MIPS. We find that the effect of deformability on phase separation can be understood as a modification to the effective density, with higher deformability corresponding to a lower effective density. In addition, the dense regions become increasingly disordered as deformability increases. Our results contextualize the applicability of MIPS to biological systems and have implications for how cells in biological systems may self-organize.