After establishing my group at Leiden University, in 2014, I have devoted myself to exploring the fuzzy interface between soft matter and biology, using the universal language of geometry and mechanics and following the North Star of experimental evidence. This endeavour resulted into several exciting discoveries, such as those related with the dynamics of defects in active matter, the geometry of bacterial monolayers and the origin of their transition to multilayered structures, the dynamics of cooperative sperm aggregates in competitive environments, the geometry and thermodynamics of lipid mixtures on curved topographies etc. Starting from 2018, I embarked in a comprehensive research program aimed at deciphering the seemingly endless complexity of epithelial tissues.

Abstract:

Collective migration and topological phase transitions in confluent epithelia.

Collective epithelial migration leverages on topological rearrangements of the intercellular junctions, which allow cells to intercalate without loosing confluency. In silico studies have provided a clear indication that this process could occur via a two-step phase transition, where a hierarchy of topological excitations progressively transforms an epithelial layer from a crystalline solid to an isotropic liquid, via an intermediate hexatic liquid crystal phase. Yet, the fundamental mechanism behind this process and its implications for collective cell behavior are presently unknown. In this talk I will show that the on set of collective cell migration in cell-resolved models of epithelial layers takes place via an activity-driven melting transition,characterized by an exponentially-divergent correlation length across the solid/hexatic phase boundary. Using a combination of numerical simulations and Renormalization Group analysis, I will show that the availability of topologically distinct rearrangements - known as T1 andT2 processes - and of a non-thermal route to melting, renders the transition significantly more versatile and tunable than int wo-dimensional passive matter. Specifically, the relative frequency ofT1 and T2 processes and of the "bare" stiffness of the cell layer affect the divergence of positional correlations within a well-defined spectrum of critical behaviors. Suppressing T1 processes, changes the nature of the transition by preventing collective migration in favor of a cellular analog of surface sublimation.