Oscillatory Microrheology, Creep Compliance and Stress Relaxation of Biological Cells Reveal Strong Correlations as Probed by Atomic Force Microscopy

Abstract

The mechanical properties of cells are important for many biological processes, including wound healing, cancers, and embryogenesis. Currently, our understanding of cell mechanical properties remains incomplete. Different techniques have been used to probe different aspects of the mechanical properties of cells, among them microplate rheology, optical tweezers, micropipette aspiration, and magnetic twisting cytometry. These techniques have given rise to different theoretical descriptions, reaching from simple Kelvin-Voigt or Maxwell models to fractional such as power law models, and their combinations. Atomic force microscopy (AFM) is a flexible technique that enables global and local probing of adherent cells. Here, using an AFM, we indented single retinal pigmented epithelium cells adhering to the bottom of a culture dish. The indentation was performed at two locations: above the nucleus, and towards the periphery of the cell. We applied creep compliance, stress relaxation, and oscillatory rheological tests to wild type and drug modified cells. Considering known fractional and semi-fractional descriptions, we found the extracted parameters to correlate. Moreover, the Young’s modulus as obtained from the initial indentation strongly correlated with all of the parameters from the applied power-law descriptions. Our study shows that the results from different rheological tests are directly comparable. This can be used in the future, for example, to reduce the number of measurements in planned experiments. Apparently, under these experimental conditions, the cells possess a limited number of degrees of freedom as their rheological properties change.

Nanorheology and Nanoindentation Revealed a Softening and an Increased Viscous Fluidity of Adherent Mammalian Cells upon Increasing the Frequency

“…Similar dependencies with the frequency were reported for the storage and loss moduli. [ 14,26,43 ] The cross‐over between the storage and the loss moduli has been observed before on many types of mammalian cells such as fibroblasts, [ 13 ] Hela cells, [ 14 ] retinal pigmented epithelium cells [ 34 ] or kidney epithelial cells. [ 26,43 ]…”

Mechanical Properties of Colorectal Cancer Cells Determined by Dynamic Atomic Force Microscopy: A Novel Biomarker

“…Here, we swept the frequency of this modulation to acquire the storage modulus (G′) and the loss modulus (G″) as a function of frequency. From frequency-dependent data, we could acquire the power-law exponent in a certain frequency range (here, from 1 to 100 Hz), which several authors correlated with the cytosol cell fluidity [ 13 ] and is known to determine the ability of cells to change their shape and contract during motile processes [ 28 , 29 ].…”

Harnessing atomic force microscopy‐based single‐cell analysis to advance physical oncology

“…During tumor metastasis, cancer cells need to invade through local tissue, squeeze into blood or lymphatic vessels, survive the harsh fluidic conditions within those vessels, squeeze out of them, and finally begin growing in a new site (Kiberstis, 2016) (Figure 8a). The fluid mechanics (e.g., flow rates, vessel size, shear stress) of the blood and lymphatic circulatory systems has been shown to significantly influence the behaviors of cancer cells, and cancer cells further exploit the underlying physical forces within these fluids to successfully seed distant metastases (Follain et al, 2020). A recent study by Bera et al (Bera et al, 2022) AFM has been recently utilized to probe the mechanical properties of single cancer cells grown on stiffness-tunable substrates under fluidic flow conditions (Wei et al, 2022;Wei & Li, 2023).…”

“…The oscillations of the cantilever can be clearly discernible from the obtained force‐time curves (Figure 7b). The complex modulus ( G* ( ω )= G ′( ω ) + iG ″( ω ), G ′( ω ) is the storage modulus reflecting the elastic properties, and G ″( ω ) is the loss modulus reflecting the viscous properties) of the cell is then calculated from the force curves by Fourier analysis (Alcaraz et al, 2003; Flormann et al, 2021). By adjusting the frequencies of the sinusoidal oscillations exerted on the AFM cantilever, the frequency‐dependent dynamic mechanical properties of cells can then be obtained.…”