PingGen Cai

Temporal Variation in Single-Cell Power-Law Rheology Spans the Ensemble Variation of Cell Population

Changes in the cytoskeletal organization within cells can be characterized by large spatial and temporal variations in rheological properties of the cell (e.g., the complex shear modulus G∗). Although the ensemble variation in G∗ of single cells has been elucidated, the detailed temporal variation of G∗ remains unknown. In this study, we investigated how the rheological properties of individual fibroblast cells change under a spatially confined environment in which the cell translational motion is highly restricted and the whole cell shape remains unchanged. The temporal evolution of single-cell rheology was probed at the same measurement location within the cell, using atomic force microscopy-based oscillatory deformation. The measurements reveal that the temporal variation in the power-law rheology of cells is quantitatively consistent with the ensemble variation, indicating that the cell system satisfies an ergodic hypothesis in which the temporal statistics are identical to the ensemble statistics. The autocorrelation of G∗ implies that the cell mechanical state evolves in the ensemble of possible states with a characteristic timescale.

Temporal change in complex shear modulus of cells: An atomic force microscopy study

To sort living cells according to our needs, it is important to understand how degree cell property measured for cell sorting fluctuates in time. Mechanical property of cells is one of essential indicators for cell sorting. Thus, in this study, we attempted to measure a time evolution of viscoelastic property such as complex shear modulus, G* of single cells adhered on substrates using atomic force microscopy (AFM). We observed that the G* largely fluctuated in time even the cells are placed on substrates in a confined condition. This indicates that in mechanical cell sorting, mechanical fluctuations of cells should be carefully estimated so that cells are precisely separated by taking the measured data involving cell fluctuations into account.