Stress relaxation and creep on living cells with the atomic force microscope: a means to calculate elastic moduli and viscosities of cell components

Abstract

In this work we present a unified method to study the mechanical properties of cells using the atomic force microscope. Stress relaxation and creep compliance measurements permitted us to determine, the relaxation times, the Young moduli and the viscosity of breast cancer cells (MCF-7). The results show that the mechanical behaviour of MCF-7 cells responds to a two-layered model of similar elasticity but differing viscosity. Treatment of MCF-7 cells with an actin-depolymerising agent results in an overall decrease in both cell elasticity and viscosity, however to a different extent for each layer. The layer that undergoes the smaller decrease (36–38%) is assigned to the cell membrane/cortex while the layer that experiences the larger decrease (70–80%) is attributed to the cell cytoplasm. The combination of the method presented in this work, together with the approach based on stress relaxation microscopy (Moreno-Flores et al 2010 J. Biomech. 43 349–54), constitutes a unique AFM-based experimental framework to study cell mechanics. This methodology can also be extended to study the mechanical properties of biomaterials in general.

Temperature dependent stiffness and visco-elastic behaviour of lipid coated microbubbles using atomic force microscopy

“…Creep and relaxation testing has been successfully carried out, at the micro-level, on cartilage and bone 26 and recently on living cells. 27 It is also worth noting that the visco-elastic properties of materials are generally known to be sensitive to temperature.…”

Measuring the Stiffness of <em>Ex Vivo</em> Mouse Aortas Using Atomic Force Microscopy

“…To probe the mechanics of the sub-endothelial layers of arterial samples, larger colloidal probes (10 -20 µm in diameter) could be used for indentation and changes in the calculated stiffness with indentation depth could be determined 22,23 . Also, since biological samples are usually viscoelastic rather than purely elastic, stress relaxation measurements (monitoring the decay in applied force at a constant indentation depth) could be used to determine the viscous component of arterial mechanical properties 24,25 .…”

Stiffness Dependent Separation of Cells in a Microfluidic Device

“…The applied force was sufficient to indent cells approximately 4mm. These values for the AFM parameters were selected to serve the purpose of comparing results with previous studies [38,39,42,43]. The force-indentation curve was obtained for each measurement and then analyzed with a Hertzian model for a pyramidal tip (Wavemetrics, IgorPro software routines) from which the Young's modulus values were calculated.…”