Figure 4.

Diffusion coefficient of nanoparticles and viscosity of the cytoplasm of parental fibroblasts, derived hiPS cells, and hES cells. (A) Viscous and elastic fractions of particles observed in each condition. Particles were classified as viscous if their MSDs at a time-lag of 10 s were ≥0.000125 μm²/s. (B) Mean diffusion coefficient, $\overline{D}$, of embedded beads. The MSDs of freely diffuse beads up to a time-lag of 1s were used to determine the bulk mean diffusion coefficient of beads in IMR90 and hiPS cells to be 0.00028 ± 0.00003 and 0.00054 ± 0.00004, μm²/s, respectively. Asterisks or indications of no significance (NS) correspond to P values of t-tests between IMR90 values and each respective column. (C) Cytoplasmic viscosity is inversely related to the diffusion coefficient through the Stokes-Einstein relationship (see text). The mean viscosities, $\overline{\eta }$, of IMR90 and hiPS cells are 24 ± 3 and 15 ± 1 Poise, respectively (P < 0.0001). Asterisks or indications of NS correspond to P values of t-tests between IMR90 values and each respective column. (D) Mean elastic modulus, ${\overline{G}}^{\prime }$, at 1 Hz calculated using only time-independent MSDs representative of elastic particles in each condition. Asterisks or indications of NS correspond to P values of t-tests between IMR90 values and each respective column.