Measuring (biological) materials mechanics with atomic force microscopy. 2. Influence of the loading rate and applied force (colloidal particles)

• Published in: Microscopy research and technique 2021-05, Vol.84 (5), p.1078-1088
• Main Authors: Weber, Andreas, Zbiral, Barbara, Iturri, Jagoba, Benitez, Rafael, Toca‐Herrera, José L.
• Format: Article
• Language: English
• Subjects: Atomic force microscopy; cell mechanics; colloidal force probe; Diameters; Endothelial Cells; Load distribution; Loading rate; Mechanical measurement; Mechanical Phenomena; Mechanical properties; Microscopy; Microscopy, Atomic Force; power law rheology; Spectroscopy; Stiffening; Viscoelasticity; Young's modulus
• ISSN: 1059-910X; 1097-0029
• DOI: 10.1002/jemt.23643

Atomic force microscopy (AFM) is the most often used tool to study the mechanical properties of eukaryotic cells. Due to their complex assembly, cells show viscoelastic properties. When performing experiments, one has to consider the influence of both loading rate and maximum load on the measured mechanical properties. Here, we employed colloidal particles of various sizes (from 2 to 20 μm diameter) to perform force spectroscopy measurements on endothelial cells at loading rates varying from 0.1 to 50 μm/s, and maximum loads ranging from 1 to 25 nN. We were able to determine the non‐linear dependence of cell viscoelastic properties on the loading rate which followed a weak power law. In addition, we show that previous loading at high forces leads to a stiffening of cells. Based on these results we discuss a road map for determining cell mechanical properties using AFM. Finally, this work provides an experimental framework for cell mechanical measurements using force‐cycle experiments. This work shows the non‐linear dependence of cell mechanical properties on loading rate when using an AFM. Guidelines and pitfalls for performing cell mechanical studies by nanoindentation are provided.