Figure 6: Indentation induced damage and fracture behavior in the spike cuticle. (A-B) SE-SEM images of cracks produced by high-load indentation at 1000 µN in the striated region which are stopped at the outer helicoidal region as seen both at low (A, scale bar: 20µm) and high (B, scale bar: 5µm) high magnification. (C-D) BSE-SEM images of cracks produced by high-load indentation at 200 µN in the highly mineralized region observed at low (C, scale bar: 20µm) and high (D, scale bar: 5µm) magnification. (E-F) SE-SEM images of the interface between the highly mineralized region and the outer helicoidal region in a fractured sample showing the deviation of the fracture plane in correspondence of the outer helicoidal region (E, scale bar: 10µm). (F) The presence of vertical chitin-protein fibers belonging to pore canals (arrow heads) and bridging horizontal fibers beds is highlighted (scale bar: 5µm). HMR: highly mineralized region; OHR: outer helicoidal region; STR: striated region; TR: transition region.