The effects of confluency on cell mechanical properties.

Mechanical properties of cells depend on various external and internal factors, like substrate stiffness and surface modifications, cell ageing and disease state. Some other currently unknown factors may exist. In this study we used force spectroscopy by AFM, confocal microscopy and flow cytometry to investigate the difference between single non-confluent and confluent (in monolayer) Vero cells. In all cases the stiffness values were fitted by log-normal rather than normal distribution. Log-normal distribution was also found for an amount of cortical actin in cells by flow cytometry. Cells in the monolayer were characterized by a significantly lower (1.4-1.7 times) Young's modulus and amount of cortical actin than in either of the single non-confluent cells or cells migrating in the experimental wound. Young's modulus as a function of indentation speed followed a weak power law for all the studied cell states, while the value of the exponent was higher for cells growing in monolayer. These results show that intercellular contacts and cell motile state significantly influence the cell mechanical properties.