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Cells ability to sense the physical properties of their microenvironment is a critical feature for tissue homeostasis (Jaalouk and Jan Lammerding 2009). Current evidence makes a strong case for a bidirectional relationship between nanoscale integrin-mediated adhesion and mechanical forces genesis in that process. This ability of cells to integrate information coming from their physical environment is expressed through the concept of mechanotransduction which involve dynamic feedback loops between mechanical stimuli and biochemical signals. Classical genetic approaches have pointed out the major role of the cell contractile machinery elements (adhesive proteins, cell cytoskeleton) in that process without giving access to the dynamics of mechanotransduction processes. This project aims at probing the dynamic relation of mechanotransduction between mechanical and biochemical cues using a combination of optogenetic (input generator) and time resolved Traction Force Microscopy (functional output), microfabrication and advanced optics. The main goal is to uncode cells sense of touch in order to be able to perform an optical control of cell nano-mechanical activity.

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The process of converting physical forces into biochemical signals and integrating these signals into the cellular responses is referred to as mechanotransduction. Force transmission is achieved via focal adhesions, which form a physical link between the actin cytoskeleton and the extracellular matrix. The different biochemical signals are in turn integrated by the cells, which consequently control important functions crucial for the cell survival. When a cell adheres to an underlying substrate, it exerts traction forces on the substrate to enable migration. Cell traction forces are also essential for controlling cell shape and maintaining cellular homeostasis. In order to measure these cell traction forces, a cell traction force microscope is typically used. This technique relies on the optical tracking of fluorescent microbeads embedded in an elastic substrate to determine deformation of substrate and the use of elasticity theory for the calculation of the traction forces. But, dynamical experiments are not possible since spatial and temporal control cannot be achieved through a passive substrate. Therefore, the main objective of this project is the incorporation of magnetic particles in a flexible polyacrylamide gel and the application of a dynamical mechanical strain a spatial and temporal control through a magnetic micromanipulator. With this new technique, both the application of the external force and the measurement of the cellular forces will be done through the active substrate in a pseudo-physiological situation.