The results have been investigated by Atomic Force Microscopy (AFM), Optical Tweezers (OT), Magnetic Twisting Cytometry (MTC) and other techniques. In the past few years a variety of cell rheology techniques have been developed in order to characterize different cell types under different physiological conditions. The structural damping law, according to which the ratio of loss to storage is independent of frequency, is used to interpret this behavior. The cytoskeleton can be modeled as an active soft glassy material (SGM) with storage and loss moduli varying according to the stimulus, although with important differences. These measurements show that cells actively respond to stretch, leading the cytoskeleton to become more solid-like for a constant stretch and more liquid-like for a transient one. Rheology measurements have revealed that the cytoskeleton response to external stimuli shows a universal behavior, characterized by a fractal power law dependence with frequency. Hence, modeling and characterizing the viscoelastic properties of the cytoskeleton in qualitative and quantitative ways allows for a better understanding of cell biomechanics and signal transduction. This highly dynamic network of proteins responds to chemical and mechanical signals by reorganizing its molecular structure and changing its properties in response to a stimulatory signal. The ability of cells to soften and/or stiffen their internal structures relies on the viscoelastic nature of their cytoskeleton. Softening is also important for embryonic stem cells, which were shown to be more responsive to the application of small cyclic stresses than when they are in a stiffer and differentiated state and for astrocytes, which tend to soften after a traumatic mechanical injury. For neuronal cells, stiffening is related to Alzheimer’s disease, unlike cancer cells, that tend to soften, in order to facilitate metastasis. It has also been shown that in the course of some diseases like malaria, asthma or arthritis, cells take on a stiffer state. We refer to this ensemble as “membrane-cortex complex” (MCC).Īlthough the detailed mechanism of those mechano-biological processes is still unclear, it has been demonstrated that cells are able to sense and to adapt to the stiffness of the substrate. The cell cortex is a thin cross-linked actomyosin layer immediately beneath the plasma membrane, to which it is connected by transmembrane proteins. Those properties play important roles in a variety of cell processes like growth, division, migration, differentiation and phagocytosis. It has been shown that the elastic properties of the membrane-cortex complex are related to the cell biological functions. ConclusionsĪlthough some discrepancies with previous results remain and may be inevitable in view of natural variability, the methodology developed in this work allows us to explore the viscoelastic behavior of the membrane-cortex complex of different cell types as well as to compare their viscous and elastic moduli, obtained under identical and well-defined experimental conditions, relating them to the cell functions.Ĭells in their natural environment are continually subjected to internal and external forces that influence their behavior. Among the three cell types, astrocytes have the lowest elastic modulus, while neurons and fibroblasts exhibit a more solid-like behavior. The obtained viscoelastic moduli are in the order of Pa. Employing the soft glass rheology model, we obtain the scaling exponent and the Young’s modulus for each cell type. These two parameters were carefully measured for the three cell types used. To avoid distortions associated with cell probing techniques, we use a previously developed method that takes into account the influence of under bead cell thickness and bead immersion. In this work we develop and apply a new methodology based on optical tweezers to investigate the rheological behavior of fibroblasts, neurons and astrocytes in the frequency range from 1Hz to 35Hz, determining the storage and loss moduli of their membrane-cortex complex. ![]() This has been attributed to differences in techniques and models for cell response as well as to the natural variability of cells. However, the experimental data reported in literature for viscoelastic moduli differ by up to three orders of magnitude. ![]() The viscoelastic properties of cells have been investigated by a variety of techniques.
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