title: Viscoelastic Properties of Confluent MDCK II Cells Obtained from Force Cycle Experiments.
abstract: The local mechanical properties of cells are frequently probed by force indentation experiments carried out with an atomic force microscope. Application of common contact models provides a single parameter, the Young's modulus, to describe the elastic properties of cells. The viscoelastic response of cells, however, is generally measured in separate microrheological experiments that provide complex shear moduli as a function of time or frequency. Here, we present a straightforward way to obtain rheological properties of cells from regular force distance curves collected in typical force indentation measurements. The method allows us to record the stress-strain relationship as well as changes in the weak power law of the viscoelastic moduli. We derive an analytical function based on the elastic-viscoelastic correspondence principle applied to Hertzian contact mechanics to model both indentation and retraction curves. Rheological properties are described by standard viscoelastic models and the paradigmatic weak power law found to interpret the viscoelastic properties of living cells best. We compare our method with atomic force microscopy-based active oscillatory microrheology and show that the method to determine the power law coefficient is robust against drift and largely independent of the indentation depth and indenter geometry. Cells were subject to Cytochalasin D treatment to provoke a drastic change in the power law coefficient and to demonstrate the feasibility of the approach to capture rheological changes extremely fast and precisely. The method is easily adaptable to different indenter geometries and acquires viscoelastic data with high spatiotemporal resolution.
authors.affiliation: Georg-August-Universität Göttingen, Institute of Physical Chemistry, Göttingen, Germany.
authors.forename: Bastian Rouven
authors.initials: BR
authors.lastname: Brückner
authors.affiliation: Georg-August-Universität Göttingen, Institute of Physical Chemistry, Göttingen, Germany.
authors.forename: Helen
authors.initials: H
authors.lastname: Nöding
authors.affiliation: Georg-August-Universität Göttingen, Institute of Physical Chemistry, Göttingen, Germany. Electronic address: ajansho@gwdg.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Janshoff
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D015638:Cytochalasin D / Q000378:metabolism; D004285:Dogs; D004548:Elasticity; D061985:Madin Darby Canine Kidney Cells; D012212:Rheology; D014783:Viscosity
chemical_list: D000199:Actins; D015638:Cytochalasin D