Cell division plays an important role in regulating cell proliferation and differentiation. It is managed by a complex sequence of cytoskeleton alteration that induces dividing cells to change their morphology to facilitate their division. The change in cytoskeleton structure is expected to affect the intracellular viscoelasticity, which may also contribute to cellular dynamic deformation during cell division. However, the intracellular viscoelasticity during cell division is not yet well understood. In this study, we injected 100-nm (diameter) carboxylated polystyrene beads into the cytoplasm of HeLa cells and applied video particle tracking microrheology to measure their intracellular viscoelasticity at different phases during cell division. The Brownian motion of the intracellular nanoprobes was analyzed to compute the viscoelasticity of HeLa cells in terms of the elastic modulus and viscous modulus as a function of frequency. Our experimental results indicate that during the course of cell division, both intracellular elasticity and viscosity increase in the transition from the metaphase to the anaphase, plausibly due to the remodeling of cytoskeleton and redistributions of molecular motors, but remain approximately the same from the anaphase to the telophase.
In this paper, we report the viscoelastic properties of sodium polystyrene sulfonate (NaPSS) solution with
different concentrations (in the range of 10-4 M to 10-3 M) and with different molecular weights (70 kDa vs. 200 kDa)
investigated via Diffusing Wave Spectroscopy (DWS). The viscoelastic properties of the sample solutions are
characterized in terms of the elastic modulus G' and the viscous modulus G" as a function of frequency (f), and also
in terms of the polymer disentanglement time (τ); the effect of polymer concentration and molecular weight on these
parameters are presented. Our experimental results indicate that (1) both the viscous modulus G" and the
disentanglement time (τ) increase with molecular concentration, whereas the elastic modulus G' is relatively
insensitive to molecular concentration, and (2) for the same concentration, all the 3 parameters (i.e., the elastic
modulus G', the viscous modulus G", and disentanglement time τ) increase as the molecular weight increases.
In this paper, we briefly review earlier approaches for optical stretching of red blood cells (RBCs) and introduce a novel
approach based on oscillatory optical tweezers. Preliminary experimental data for optical trap-and-stretch of RBCs by
two approaches, namely the counter-propagating dual-beam trap-and-stretch and the oscillatory optical tweezers, are
presented and discussed.
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