Measuring the Elastic Properties of Living Cells

Cell's elasticity is an integrative parameter summarizing the biophysical outcome of many known and unknown cellular processes. This includes intracellular signaling, cytoskeletal activity, changes of cell volume and morphology, and many others. Not only intracellular processes defines a cell's elasticity but also environmental factors like their biochemical and biophysical surroundings. Therefore, cell mechanics represents a comprehensive variable of life. A cell in its standard conditions shows variabilities of biochemical and biophysical processes resulting in a certain range of cell's elasticity. Changes of the standard conditions, endogenously or exogenously induced, are frequently paralleled by changes of cell elasticity. Therefore, cell elasticity could serve as a parameter to characterize different states of a cell. Atomic force microscopy (AFM) combines high spatial resolution with very high force sensitivity and allows investigating mechanical properties of living cells under physiological conditions. However, elastic moduli reported in the literature showed a large variability, sometimes by an order of magnitude (or even more) for the same cell type assessed in different labs. Clearly, a prerequisite for the use of cell elasticity to describe the actual cell status is a standardized procedure that allows obtaining comparable values of a cell independent from the instrument, the lab, and operator. Biologically derived variations of elasticity could not be reduced due to the nature of living cells, but technically and methodologically derived variations could be minimized by a standardized procedure.This chapter provides a Standardized Nanomechanical AFM Procedure (SNAP) that strongly reduces the variability of results obtained on soft samples and living cells by a reliable method to calibrate AFM cantilevers.