Figure 2
Measuring the response of the nucleus at different deformation length- and time-scales. (a) Inset shows the motion of the piezo-element that moves the base of the cantilever with increasing frequencies at a constant amplitude of 25 nm. The main panel shows the cantilever bending at its free end. Higher bending means more resistance, which can be induced by the compliance of the nucleus but also by the drag of the surrounding buffer. The latter is corrected for in the analysis. (b) At low deformation rates of 1 Hz, E* is not constant but increases threefold when the indentation depth is increased from 0.5 to 2.6 µm. At higher deformation rates up to 700 Hz, the dependency on the indentation remains. In addition, the modulus increases multi-fold with frequency. E* below and above the estimated threshold of 100 Hz had been fitted with a power law (dashed black line). The slope at low and high frequency are 0.22 and 0.60 at 1 nN, 0.22 and 0.46 at 4 nN and 0.24 and 0.38 at 15 nN. (c) The complex Young’s modulus can be decomposed in its viscous (E″) and elastic (E′) components. The ratio E″/E′ (loss tangent), shows that the viscous contribution is small at high deformations and low frequencies. Only at small deformations and higher frequencies does the viscosity contribution becomes more pronounced. The data is shown as the mean ± standard error of the mean of the log transformed data (shaded area).
