Relative Microelastic Mapping of Living Cells by Atomic Force Microscopy

TLDR

The mechanical properties of living cells change spatially and temporally, reflecting complex physiological processes, and AFM indentation provides local viscoelastic information. The study aims to develop FIEL mapping with AFM to generate robust, internally quantitative maps of relative elasticity, thereby providing insight into cellular mechanics and regulation. FIEL mapping collects force‑distance curves on a fast timescale to minimize viscous effects, using AFM to produce robust, internally quantitative maps of relative elasticity. FIEL mapping, independent of tip‑sample contact point and cantilever spring constant, reveals that elasticity in MDCK cells is uncoupled from topography, uncovering unexpected features and enabling high‑resolution mechanical contrast.

Abstract

The spatial and temporal changes of the mechanical properties of living cells reflect complex underlying physiological processes. Following these changes should provide valuable insight into the biological importance of cellular mechanics and their regulation. The tip of an atomic force microscope (AFM) can be used to indent soft samples, and the force versus indentation measurement provides information about the local viscoelasticity. By collecting force-distance curves on a time scale where viscous contributions are small, the forces measured are dominated by the elastic properties of the sample. We have developed an experimental approach, using atomic force microscopy, called force integration to equal limits (FIEL) mapping, to produce robust, internally quantitative 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 canine kidney (MDCK) cells show that elasticity is uncoupled from topography and reveal a number of unexpected features. These results present a mode of high-resolution visualization in which the contrast is based on the mechanical properties of the sample.