Atomic force microscopy probing in the measurement of cell mechanics

Abstract

Atomic force microscope (AFM) has been used incrementally over the last decade in cell biology. Beyond its usefulness in high resolution imaging, AFM also has unique capabilities for probing the viscoelastic properties of living cells in culture and, even more, mapping the spatial distribution of cell mechanical properties, providing thus an indirect indicator of the structure and function of the underlying cytoskeleton and cell organelles. AFM measurements have boosted our understanding of cell mechanics in normal and diseased states and provide future potential in the study of disease pathophysiology and in the establishment of novel diagnostic and treatment options.

Keywords: atomic force microscopy; cell elastography; cell force spectroscopy; cell mechanics.

Figure 1

The AFM cell indentation experiment. A) The force curve obtained by measurements of cantilever deflection versus z-position during advancement and retraction of the probe. This curve provides information about the viscoelastic properties of the cell. Once the raw force curve is obtained and the contact point (Z₀) identified, cell mechanical properties are obtained from the analysis of the curve of indentation force (F = k × h) versus depth (D = (Z − Z₀) − h) B).

Figure 2

A nonlinear stress–strain relation (solid line) characterizes most biological soft tissues, with a viscoelastic hysteresis between loading and unloading segments of the curve, as opposed to the linear stress–strain curve of an idealized elastic material which is characterized by the Young’s modulus obtained from the slope of the line.