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Abstract

As all living organisms are composed of cells, cellular research is indispensable to understanding life. Consequently, efforts to understand the behavior of cells and populations of cells from a physics perspective are advancing. When addressing mechanical aspects such as cell motility and forces, it has become clear that the behavior of cell populations shows greater agreement between theory and experiment than that of single cells. This involves physical principles such as symmetry and the dominance of slow variables. This lecture addresses two problems concerning cells. One is the behavior of monolayers formed by motile cells, and the other is the problem of growing cell aggregates (organoids). Animals form their morphology during development by creating cavities (lumens) within cell aggregates and folding the resulting monolayers inward. Therefore, understanding the dynamics of monolayers and cavity formation within cell aggregates forms the foundation of cell collective research. This lecture introduces two studies: ① Research investigating the role of directional order and topological defects in cell sheets, deriving a continuum model from individual cell movements and interactions, and comparing it with experiments. ② Research examining the mechanism by which a central lumen forms in organoids growing from a few cells, while the monolayer remains stable during growth, through a comparison of a model and experiments