The relation between physical interactions and structure in living cells

The following project aims to understand the physical behaviour of living cells and its connection with cell structure in a comprehensive manner, using combined microscopic techniques and physical laws. Comprehensive here means, cells will be treated as they are: complex entities whose behaviour is the outcome of well-coordinated exo- and intracellular signalling framed in an integrated dynamic structure of membranes and tubular-fibrillar network. Scanning probe microscopy (SPM) and optical microscopy (OM) will be used to study non-contact cell interactions as well as cell contact mechanics (i.e. contact cell interactions) and explore the role of the different cell constituents mainly involved, i.e. cell membrane and glycocalyx as well as cell cytoskeleton and cell organelles. The experimental focus is three fold: first, the long- and short range forces arising between the cell surface and an approaching microsized probe (a colloidal particle or a sharp pointed tip attached to a cantilever); second, the stress and strains occurring in the cell when the probe is in contact for a prolonged time and third, the formation of membrane tethers between the cell surface and the probe as a result of the prolonged contact, that can be elongated and eventually snapped off when the probe is withdrawn. The first should allow us to find physical fingerprints of structures within the apical cell membrane, such as the extension and continuity of the cell glycocalyx or the presence of membrane-bound supramolecular complexes; the second provides the viscoelastic parameters of the cell as they may be ascribed to its structural constituents; the third infers the capacity of cell communication by building up membrane tubules. The first and the second focuses will be studied at two different size scales: locally, with small, nanometre-sized probes and globally, with big, microscopically sized probes. The overall behaviour of living cells will be compared to that of synthetic models made of giant vesicles. The constituents of these synthetic models will mimic the cell membrane and the cell cytoskeleton and they will be used to evaluate the contribution of the isolated cell constituents and of the structural complexity (i.e. structural interconnectivity) to the cell physical response.