Fig. 3.

Normalized force-displacement curves measured in the cytoplasm of NRK cells show that the cytoplasm exhibits viscoelasticity under small effective strain rate and exhibits poroelasticity under large effective strain rate. Each curve shown here is averaged over at least 20 individual experiments. (A) Under low effective strain rate, the normalized force-displacement curves obtained with different bead sizes (0.5, 1, and 1.5 µm) are close to each other when the same V/a is maintained (e.g., 1 s⁻¹ and 0.2 s⁻¹). (Inset) Normalized force-displacement curves with different bead sizes are clearly separated when we compare experiments with the same Va in the low-speed regime. (B) Under high effective strain rate, the normalized force-displacement curves with different bead sizes (0.5, 1, and 1.5 µm) are close to each other when the same Va is maintained (e.g., 15 µm²/s and 10 µm²/s). (Inset) Normalized force-displacement curves with different bead sizes are clearly separated when we compare experiments with the same V/a in the high-speed regime.