After a lecture on active matter in 2019, the two lectures in 2020 and 2021 will be devoted to the physics of tissues that can be considered as examples of active matter. The lectures emphasize the active character of tissues, but they also try to show what a physicist's approach can bring to tissue biology by essentially discussing two types of tissue : cancer tissues and tissues of early animal development. I wished to dedicate this 2020 lecture to the memory of Suzanne Eaton, who performed many of the experiments described in the lecture and who was brutally murdered in 2019.
The 2020 lecture began with a fairly general description of tissue physics, presenting the classical physical approaches, which have been used to describe tissues such as D'Arcy Thompson's very geometric description of morphogenesis, or the mechanisms of regulation of tissue growth by morphogens proposed by Turing. The general aim of the lecture is to discuss the coupling between tissue mechanics and tissue growth, while taking into account the chemical regulation of growth.
The second part of the 2020 lecture was devoted to the study of epithelial tissues using so-called " vertex models ". These models describe epithelial tissues as two-dimensional graphs in which cells are polygons that pave the space. The tissue structure is given by the graph that locally minimizes the tissue energy. The predictions of vertex models can be compared directly with experiments on epithelial tissue during development. The examples given in the lecture are essentially those of the development of the wing imaginal disc, then of the Drosophila wing. The lecture also discusses recent developments to extend vertex models, to take into account the three-dimensional structure of cells in epithelial tissues, and the determination from microscopic tissue structure at the cell scale of locally averaged macroscopic quantities such as tissue strain or strain rate.
The 2021 lecture will present a more macroscopic approach to tissues somewhat considered as materials, with emphasis on the coupling between mechanical properties and tissue growth.