Exposure to mechanical stresses is a normal part of physiology for monolayers: intestinal epithelia are stretched during peristaltic movements in the gut, lung alveoli deform during breathing, and endothelia are exposed to pulsatile fluid shear stresses in blood flow ( 1 – 3). Tight junctions form barriers restricting the passage of solutes while others, such as adherens junctions and desmosomes, integrate the cytoskeletons of constituent cells into a mechanical syncitium. Cells within these monolayers are tightly connected to one another by intercellular junctions.
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Many of the cavities and free surfaces of the human body are lined by a layer of cells one cell thick.
This multiscale study of monolayer response to deformation enabled by our device provides the first quantitative investigation of the link between monolayer biology and mechanics. High magnification imaging revealed that keratin filaments became progressively stretched during extension, suggesting they participate in monolayer mechanics. As in single cells, monolayer mechanical properties were strongly dependent on the integrity of the actin cytoskeleton, myosin, and intercellular adhesions interfacing adjacent cells.
Measurement of stress at fracture enabled a first estimation of the average force needed to separate cells within truly mature monolayers, approximately ninefold larger than measured in pairs of isolated cells. Monolayers could withstand more than a doubling in length before failing through rupture of intercellular junctions. Using this system, we provide measurements of monolayer elasticity and show that this is two orders of magnitude larger than the elasticity of their isolated cellular components. Here, we describe a system for tensile testing of freely suspended cultured monolayers that enables the examination of their mechanical behavior at multi-, uni-, and subcellular scales. Though resisting and generating mechanical forces is an essential part of monolayer function, simple experimental methods to characterize monolayer mechanical properties are lacking. Later, monolayers act as physical barriers separating the internal environment from the exterior and must withstand externally applied forces. In early development, embryonic morphogenesis results largely from monolayer rearrangement and deformation due to internally generated forces. One-cell-thick monolayers are the simplest tissues in multicellular organisms, yet they fulfill critical roles in development and normal physiology.
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