Rheological properties of cells measured by optical tweezers.

Diney S. Ether,Vivaldo Moura-Neto,Nathan B. Viana,Glauber R. Araujo,Susana Frases,Luis B. Pires,Bruno Pontes,Marcos Farina,H. Moysés Nussenzveig,Luciana F. Romão,Yareni A. Ayala

doi:10.1186/s13628-016-0031-4

Diney S. Ether, Vivaldo Moura-Neto

Open Access

https://doi.org/10.1186/s13628-016-0031-4

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Abstract

BackgroundThe viscoelastic properties of cells have been investigated by a variety of techniques. However, the experimental data reported in literature for viscoelastic moduli differ by up to three orders of magnitude. This has been attributed to differences in techniques and models for cell response as well as to the natural variability of cells.ResultsIn 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. 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. These two parameters were carefully measured for the three cell types used. Employing the soft glass rheology model, we obtain the scaling exponent and the Young’s modulus for each cell type. The obtained viscoelastic moduli are in the order of Pa. Among the three cell types, astrocytes have the lowest elastic modulus, while neurons and fibroblasts exhibit a more solid-like behavior.ConclusionsAlthough 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13628-016-0031-4) contains supplementary material, which is available to authorized users.

Highlights

The viscoelastic properties of cells have been investigated by a variety of techniques
The fibroblasts and astrocytes cell heights near their edges have similar values, 2.2 ± 0.1 μm, almost twice the value obtained for neurons, 1.3 ± 0.1 μm, (Fig. 2c and Table 1)
This result already suggests that the astrocyte membrane-cortex complex” (MCC) is softer when compared to neurons and fibroblasts, since, by using the same pressing force with the optical tweezers, the trapped bead penetrates deeper in astrocytes

Summary

Introduction

The viscoelastic properties of cells have been investigated by a variety of techniques. The experimental data reported in literature for viscoelastic moduli differ by up to three orders of magnitude This has been attributed to differences in techniques and models for cell response as well as to the natural variability of cells. It has been shown that the elastic properties of the membrane-cortex complex are related to the cell biological functions [3]. Those properties play important roles in a variety of cell processes like growth, division, migration, differentiation and phagocytosis [4]. The cell cortex is a thin cross-linked actomyosin layer immediately beneath the plasma membrane, to which it is connected by transmembrane proteins [4]. Softening is 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 [11, 12] and for astrocytes, which tend to soften after a traumatic mechanical injury [13]

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