Master Defense by Ariel Avanzi

Abstract: Cellular systems in Nature are inherently three-dimensional and can be modeled as multi-layer of soft cells that are able to convert energy into mechanical forces that are used to move and modify their environment. This ability, known as activity, drives numerous dynamical processes, such as tissue morphogenesis, and wound healing. Aggregates of cells coordinate their behavior to collectively self-organize in a variety of different patterns, that are the foundation of life as we know.

This study introduces a 3D phase field model that is based on cellular deformation and the transmission of mechanical forces both within and beyond the layers of cells. The interactions are captured by adhesion and repulsion at the cell interface and an interacting solid scaffold is introduced to understand tissue formation on a substrate. The numerical implementation shows the criteria that allow the cells to merge into a single layer, pointing out the relevance of cellular re-organization, while different patterns arise from the analysis of its mechanics.

Forces and stresses that arise locally, are transmitted to the whole multicellular system, showing coordination in response to a change in the environment. The same type of collective response is driving the system in different configurations according to the degree of activity of the cells, highlighting the importance of this ability. The main purpose of this thesis has been to construct a valid framework for understanding complex multilayer cellular phenomena. Starting from this general framework, more layers of complexity can be added to account for more complex geometries, and different cellular interactions within cells and beyond.