Figure 5: Nanomechanical properties of the spike cuticle measured by depth sensing nanoindentation. (A) Profile plots of indentation modulus and hardness from the exterior to the interior of the cuticle on a transverse cross-section (the nanoindentation grid is visible on the light micrograph). A drop in local mechanical properties within the outer helicoidal region (OHR) is evident. (B-C) Spatial variation of indentation modulus, E, measured with higher lateral resolution from the highly mineralized to the striated region, considering both (B) transverse and (C) longitudinal cross-sections. (D-E) High resolution maps of indentation modulus focusing on the transition between HMR and STR on (D) transverse and (E) longitudinal cross-sections. Probed areas are highlighted in squares on the light micrographs and lines indicate the position of the mechanical profiles shown in B and C. HMR: highly mineralized region; IHR: inner helicoidal region OHR: outer helicoidal region; STR: striated region and TR: transition region.