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cellTL2010 - Tribol Lett(2010 38:107113 DOI...

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ORIGINAL PAPER Nanomechanical Probes of Single Corneal Epithelial Cells: Shear Stress and Elastic Modulus Joelle P. Straehla F. T. Limpoco Natalia V. Dolgova Benjamin G. Keselowsky W. Gregory Sawyer Scott S. Perry Received: 30 June 2009 / Accepted: 12 January 2010 / Published online: 30 January 2010 Ó Springer Science+Business Media, LLC 2010 Abstract Living human corneal epithelial cells have been probed in vitro via atomic force microscopy, reveal- ing the frictional characteristics of single cells. Under cell media, measured shear stresses of 0.40 kPa demonstrate the high lubricity of epithelial cell surfaces in contact with a microsphere probe. The mechanical properties of indi- vidual epithelial cells have been further probed through nanometer scale indentation measurements. A simple elastic foundation model, based on experimentally verifi- able parameters, is used to fit the indentation data, pro- ducing an effective elastic modulus of 16.5 kPa and highlighting the highly compliant nature of the cell surface. The elastic foundation model is found to more accurately fit the experimental data, to avoid unverifiable assump- tions, and to produce a modulus significantly higher than that of the widely used Hertz–Sneddon model. Keywords Atomic force microscopy ± Elastic modulus ± Shear stress ± Friction ± Epithelial cells 1 Introduction The structure and function of living cells is strongly dependent on local environment, entailing factors related to both chemical and mechanical stimuli [ 1 ]. Cell struc- ture and growth rely upon the transport of biochemical species across membranes, processes intimately related to chemical gradients and signals within the environment. Furthermore, it is now understood that mechanical forces acting on and within the cell can trigger specific cellular responses. As a result, the relationship between mechan- ical forces and the response and function of living cells is of growing interest. For example, prior work has explored the response of cell modulus to changes in the microen- vironment as well as a function of the health of the cell [ 2 ]. In addition, a significant body of work has explored cellular properties as a function of shear environment, primarily documenting the influence of shear at cell– liquid interfaces. The focus of these studies has been to identify active mechanobiological mechanisms under physiological conditions [ 3 ]. In the emerging area of mechanobiology, effort is also needed in the development of techniques used to probe the mechanical properties of biological entities as well as quantitative models used to describe these properties. In particular, techniques capable of probing individual living cells in a manner that allows access to fundamental mechanical properties are needed. These techniques ulti- mately should provide quantitative measurement of forces needed for the construction of detailed models of cellular structure and environment in addition to biomolecular sensitivity. In turn, the availability of such techniques and
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