Figure 4.

Overlaps and gaps of fibrils resolved. All measurements were performed in air and at ambient conditions with the same type of AFM tip (Tip B; see Materials and Methods). (a) Stiffness as a function of strain (i) in the interval of 65 nm < D < 81 nm and (ii) in the interval of 65 nm < D < 72 nm is shown. (b) Reconstructed longitudinal force-versus-strain curves showing the expanded range of more than 20% are shown. (c) The difference in stiffness between the gap and the overlap as a function of strain for the strain-stiffening behavior is shown. (i) The linear fit L₁ for data points in the interval 65 nm < D < 70 nm are as shown: slope = −0.07 nN/nm², R² = 0.33. The slope is significantly different from 0: p-value = 0.03. The linear fit L₂ for data points in the interval 70 nm < D < 76 nm are as follows: slope = −0.006 nN/nm², R² = 0.008. The slope is not significantly different from 0: p-value = 0.82. (ii) The number of disordered sections is greater in the gap (G), which, therefore, strain stiffens faster (L₁) than the overlap (O). At a certain strain, there is not such an excess of disordered sections in the gap anymore (L₂), and the strain stiffening in gaps and overlaps is similar. Error bars represent the standard deviations of 10 measurements per data point. To see this figure in color, go online.