Structure changes in Nephila dragline: The influence of pressure

Pressure dependent Wide Angle X-ray Scattering (WAXS) is employed to analyse the interplay between the amorphous and the nanocrystalline phases of major ampullate spider silk from Nephila edulis in the (hindered) supercontracted state. By comparing the previously published macroscopic elastic modulus with the nanocrystal modulus it is possible to quantify the contribution of the nanocrystals and the amorphous phase to the mechanical properties. From the detected shifts of the diffraction peaks the compression modulus of the nanocrystals is deduced and proven to be highest in the (100)-direction of intra-sheet hydrogen bonds. This reflects the molecular architecture of the stacked β-sheeted H-bonds within the nanocrystals. In addition, it is found that pressure may increase the organization of the amorphous phase, enhancing a diffraction ring close to the (210) reflection peak. It is more pronounced in the supercontracted state since the internal stress is released and the structure can rearrange.