Axisymmetric Contact Problem for a Flattened Cell : Contributions of Substrate Effectand Cell Thickness to the Determination of Viscoelastic Properties by Using AFM Indentation

Nanoindentation technology has proven to be an effective method to investigate the viscoelastic properties of biological cells. Theexperimental data obtained by nanoindentation are frequently interpreted by Hertz contact model. However, in order to validateHertz contact model, some studies assume that cells have infinite thickness which does not necessarily represent the real situation.In this study, a rigorous contact model based upon linear elasticity is developed for the interpretation of indentation tests of flattenedcells. The cell, normally bonded to the Petri dish, is initially treated as an elastic layer of finite thickness perfectly fixed to a rigidsubstrate. The theory of linear elasticity is utilized to solve this contact issue and then the solutions are extended to viscoelasticsituation which is regarded as a good indicator for mechanical properties of biological cells. To test the present model, AFM-based creep test has been conducted on living human hepatocellular carcinoma cell (SMMC-7721 cell) and its fullerenol-treatedcounterpart. The results indicate that the present model could not only describe very well the creep behavior of SMMC-7721 cells,but also curb overestimation of the mechanical properties due to substrate effect.