Harris, AR; (2013) From the mechanical properties of single cells to those of simple tissues. Doctoral thesis (PhD), UCL (University College London).

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Abstract

As interest in biophysics and biophysical modelling has grown in the cell and developmental biology communities, a variety of techniques have been developed to measure the mechanical properties of single cells. Atomic Force Microscopy (AFM) has become one of the preferred methods for these measurements primarily due to its ease of operation and commercial availability. However, measurements on soft cells with a variable surface topography require an additional level of care so that the predicted contact area with the cell surface is accurately estimated. Using combined AFM and confocal microscopy I have shown that with pyramidal tipped cantilevers the cell body can easily deform to the shape of the tip but can also touch the underside of the AFM cantilever beam causing an overestimation of elasticity. Such artefactual increases in contact area could be avoided by using spherical tipped cantilevers or tips with a high aspect ratio. I examined the role of the cytoskeleton and cell contractility in setting single cell stiffness with AFM. With techniques such as AFM, the rheology of single cells is becoming increasingly well characterised. The next logical step in furthering our understanding of organ and embryo mechanics is to scale up investigations to simple tissues such as on cell thick monolayers. I have developed methods to measure the mechanical properties of MDCK epithelial cell monolayers under AFM indentation or planar extension. Using deep indentation of monolayers cultured on soft gels I have measured the evolution of mechanical properties upon the establishment of cell-cell junctions. The relative mechanical stiffnesses of monolayer-gel composites evolve as cell contacts are established and required the formation of mature contractile adherens junctions. To measure the planar mechanical properties of cell monolayers I designed a system to create monolayers freely suspended from their susbstrate between two test rods. Cell monolayers have a higher stiffness than their cellular constituents due to the organisation of the cell cytoskeleton upon the formation of matured intercellular junctions.

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