Non-equilibrium Dynamics in Biological Living Matter: From Confluent Tissues to Bacterial Aggregates

Abstract 

Biological living systems are active materials where heterogeneous collections of cells generate complex non-equilibrium dynamics. In this talk, I will present how minimal physics-based descriptions provide insight into emergent behaviors across biological systems from confluent tissues to bacterial collectives. In the first part of the talk, I will discuss how distinct modes of active forces in densely packed confluent tissues influence emergent dynamics in fluid state tissues. Using the Active Foam model, we show that cell geometry, cellular rearrangement dynamics, and spatiotemporal correlations depend sensitively on active force modes, whereas a persistent Brownian motion framework yields a universal description of tissue fluidity. In the second part, I will discuss how a turning-away mechanism can enhance the navigation capabilities of bacterial aggregates in complex environments, motivated by the surface motility of Pseudomonas aeruginosa. Using a self-propelled spherocylinder model with a tunable reversal probability, we find that suppressing reversals induces a transition from homogeneous isotropic organization with diffusive motion to phase-separated, nematically ordered domains with a prolonged ballistic regime. Strikingly, we find that an intermediate collision reversal probability optimizes navigation capability by balancing trapping and directional persistence in complex environments. Together, these results demonstrate how minimal models can reveal general physical principles underlying the dynamics of living systems.

About the Speaker 

Sangwoo Kim is a tenure-track assistant professor in the Institute of Mechanical Engineering at École Polytechnique Fédérale de Lausanne (EPFL). He received his PhD in Theoretical and Applied Mechanics from the University of Illinois at Urbana-Champaign, where he investigated relationships between statistics, geometry, and mechanical states in cellular matter. After graduation, he joined the Department of Mechanical Engineering at the University of California, Santa Barbara as a postdoctoral fellow, theoretically investigating phase transition behaviors in embryonic tissues. His current research seeks to uncover the physical and mechanical principles governing biological and living systems, with broader interests in soft and active matter.

Host: Professor Sascha Hilgenfeldt