Figure 2: Microstructure of the spike. (A) Representative polished
transversal section imaged in BSE-SEM accompanied on the left by a
micro-CT reconstruction showing the location of the section. The
multilayered architecture of the cuticle, comprising a highly
mineralized region (HMR), an outer helicoidal region (OHR), a striated
region (STR) and an inner helicoidal region (IHR) is evident. (B) SE-SEM
of a longitudinal fracture offering a complementary view of the 4 layers
accompanied, on the right by, a micro-CT reconstruction showing the
location of the section. Scale bars in (A) and (B) are 200 µm. (C-E)
Details of the different layers from the polished surface. In (E), the
arrows indicate the transition region (TR) and the dotted lines bound
the OHR. In (D), horizontal parallel chitin-protein fibers are
cross-sectioned and fiber-rich strands (medium dark) alternate with pore
canal lumens (dark) and their densely mineralized sheaths (bright
rod-like features). Twisted ribbon-shaped pore canals with unmineralized
lumen also appear in (C) the IHR and (E) OHR while they are straight and
mineralized in (E) the HMR. Scale bars in (C–E): 10 µm. (F-H) Close-up
views of the fractured surface of the different layers highlighting: (F)
a rough surface for the IHR in agreement with the twisted plywood
organization; (G) sheets of parallel fibers (oriented vertically in the
figure) in the STR and (H) a rough stepwise fractured surface in
connection with the OHR (bounded by dotted lines), which is in strike
contrast with the smoother surface of the HMR. (I) Schematic summarizing
the main microstructural features of the spike. Scale bars in (F–H): 8
µm. |