Fig. 6: cAP nanocrystal deformation and residual strain as indicators of radiation damage accumulation in the bone bulk.

a Schematic illustration of a model of mineralized collagen fibers and the effects of dehydration (shrinkage, marked with brown arrow) and radiation damage (expansion, marked with magenta arrow) of the nanocrystals. Collagen shown here (triple helices within cyan pillars) runs vertically and is co-aligned with the tightly-attached axially aligned mineral cAP crystals (platelets, yellow). Together, both ingredients establish the basic building blocks of bony tissues: mineralized collagen fibers. When dehydrated, collagen condenses and due to the tight attachment, the co-aligned apatite mineral cAP crystals become compressed along the c-axis⁴⁰. Following X-ray irradiation and ionization, collagen molecules become fragmented and lose the capacity to compress the cAP crystals. b Percentage strain change within pike cleithrum bones, bovine teeth, mouse tibia, and pig jaws measured with different photon fluxes (photons per second (phs⁻¹)). For all XRD measurements, the energy was 18 keV. With accumulation of damage, the collagen backbone can no longer sustain residual compressive stress in the mineral crystals, and consequently the c-lattice parameter increases. The diffraction pattern shown for pike highlights the highly anisotropic arrangement of mineralized fibers with axial alignment of the (002) Debye rings producing upper and lower arcs.