Self-organization in active nematic surfaces

In many biological systems, a deformable surface encloses a fluidic interior. A cell or a cell nucleus are classic examples. Sometimes these surfaces are composed of active nematic materials that regulate the dynamics and morphology of the system. Examples include the cell cortex and confluent epithelial tissues. 

In this talk, I will explore theoretically the morphological dynamics of a viscous drop enclosed by a surface of active nematic material. This provides a simplified physical model for understanding the behavior of such complex active systems. Using hydrodynamic simulations, we couple fluid flow in the droplet, nematic active stresses on the surface, and interfacial deformation. This coupling gives rise to spontaneous symmetry-breaking and self-organization. We uncover a variety of dynamical regimes, including periodic braiding motion of topological defects, chaotic defect creation and annihilation, and directed motion, consistent with experimental observations. 

Further, inspired by the nuclear envelope and its nuclear pore complexes, I will also discuss the self-organization of spheroidal active nematic surfaces punctured by mobile inclusions. These inclusions partially determine the defect structures evinced by the material, through topological constraints, while also interacting dynamically with defects that are created.