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Figure 5. Examining the material properties of a cell using atomic force microscopy. (a) Because the tip of the cantilever is much stiffer (i.e. has a higher elastic modulus) than the cell, it deforms the cell membrane. (b) Using the theory of indentation, experimental force–distance curves can be compared with, and fitted to, theoretical curves and thus used to quantify cell stiffness. Raster scanning (i.e. moving the tip of the atomic force microscope progressively backwards and forwards across the surface) yields a map of the distribution of derived elasticity (c), and topographical information (d). (c) In the elasticity map, ‘hard’ areas appear as yellow, and compliant ‘softer’ areas as black. (e) The two sets of data can be merged to produce a three-dimensional representation of the topography; different colours represent different degrees of stiffness (elastic modulus) in a particular location. In (c), (d) and (e), cytoskeletal elements, which are seen as linear structures and have different material properties compared with those of the surrounding cellular elements, are marked with an arrow (fig005mhu).