Laboratoire Matière et Systèmes Complexes

There will be a live diffusion with Zoom :

Monday March 20th, 11h30 in room 454 A.

Please contact Jean-Baptiste Manneville to attend the visio-seminar.

Quantifying both viscoelasticity and surface tension of cells

Julien Husson

Ecole polytechnique, Palaiseau, France

Abstract : Quantifying the mechanical properties of cells is important to better understand how mechanics constrain cellular processes. Furthermore, as pathologies are usually paralleled by altered cell mechanical properties, mechanical parameters can be used as a novel way to characterize the pathological state of cells. Key features used in models are cell tension, cell viscoelasticity (representing the average of the cell interior), or a combination of both. It is not clear which of these features is the most relevant or if both should be included. To clarify this, we performed microindentation experiments on cells with microindenters of varying tip radii, including micron-size microneedles. We obtained different cell-indenter contact areas and measured the corresponding contact stiffness. We derived a model predicting that this contact stiffness should be an affine function of the contact radius and that at vanishing contact radius, the cell stiffness should be equal to the cell tension multiplied by a constant. When microindenting T cells and both adherent and trypsinized endothelial cells, the contact stiffness was indeed an affine function of the contact radius. For T cells, the deduced surface tension matched the one that we measured using micropipette aspiration. For detached endothelial cells, microindentation and micropipette aspirations led to inconsistent results unless the cells were considered only viscoelastic when analyzing micropipette aspiration experiments. For attached endothelial cells, we amended our model by assuming that below an elastocapillary length, the contact stiffness was constant and only due to surface tension. This work suggests that indenting cells with sharp tips while neglecting the presence of surface tension leads to an effective elastic modulus whose origin is in fact surface tension. Accordingly, using sharp tips when microindenting a cell is a good way to directly measure its surface tension without the need to let the viscoelastic modulus relax.