RELATIVE MICROELASTIC MAPPING OF LIVING CELLS BY ATOMIC-FORCE MICROSCOPY

The spatial and temporal changes of the mechanical properties of livin g cells reflect complex underlying physiological processes. Following these changes should provide valuable insight into the biological impo rtance of cellular mechanics and their regulation. The tip of an atomi c force microscope (AFM) can be used to indent soft samples, and the f orce versus indentation measurement provides information about the loc al viscoelasticity. By collecting force-distance curves on a time scal e where viscous contributions are small, the forces measured are domin ated by the elastic properties of the sample. We have developed an exp erimental approach. using atomic force microscopy, called force integr ation to equal limits (FIEL) mapping, to produce robust, internally qu antitative maps of relative elasticity. FIEL mapping has the advantage of essentially being independent of the tip-sample contact point and the cantilever spring constant. FIEL maps of living Madine-Darby canin e kidney (MDCK) cells show that elasticity is uncoupled from topograph y and reveal a number of unexpected features. These results present a mode of high-resolution visualization in which the contrast is based o n the mechanical properties of the sample.