The three-dimensional arrangement of the mineralized collagen fibers in elephant ivory and its relation to mechanical and optical properties.

Elephant tusks are composed of dentin or ivory, a hierarchical and composite biological material made of mineralized collagen fibers (MCF). The specific arrangement of the MCF is believed to be responsible for the optical and mechanical properties of the tusks. Especially the MCF organization likely contributes to the formation of the bright and dark checkerboard pattern observed on polished sections of tusks (Schreger pattern). Yet, the precise structural origin of this optical motif is still controversial. We hereby address this issue using complementary analytical methods (small and wide angle X-ray scattering, cross-polarized light microscopy and scanning electron microscopy) on elephant ivory samples and show that MCF orientation in ivory varies from the outer to the inner part of the tusk. An external cohesive layer of MCF with fiber direction perpendicular to the tusk axis wraps the mid-dentin region, where the MCF are oriented mainly along the tusk axis and arranged in a plywood-like structure with fiber orientations oscillating in a narrow angular range. This particular oscillating-plywood structure of the MCF and the birefringent properties of the collagen fibers, likely contribute to the emergence of the Schreger pattern, one of the most intriguing macroscopic optical patterns observed in mineralized tissues and of great importance for authentication issues in archeology and forensic sciences. STATEMENT OF SIGNIFICANCE: Elephant tusks are intriguing biological materials as they are composed of dentin (ivory) like teeth but have mineralized collagen fibers (MCF) similarly arranged to the ones of lamellar bones and function as bones or antlers. Here, we showed that ivory has a graded structure with varying MCF orientations and that MCF of the mid-dentin are arranged in plywood like layers with fiber orientations oscillating in a narrow angular range around the tusk axis. This organization of the MCF may contribute to ivory's mechanical properties and, together with the collagen fibers birefringence properties, strongly relates to its optical properties, i.e. the emergence of a macroscopic checkerboard pattern, well known as the Schreger pattern.

The surface layer of pharmaceutical compacts: the role of the punch surface and its impact on the mechanical properties of the compacts.

During pharmaceutical compaction, the interaction between the punch and the powder determines the formation and the aspect of the surface of the compact. In industry, the properties of the punch surface, which play a key role in this interaction, are sometimes changed by fixing an intermediate layer onto the punch to prevent sticking problems. In this article, the case of a polymer insert layer was studied. Firstly, sugar spheres were compacted with and without the polymer insert fixed onto the punches. After compaction with uncovered punches, the surface particles, which had been subjected to high deformation, were flattened on one side. However, it was observed, using confocal X-ray microfluorescence, that this kind of deformation was limited to the surface and that the bulk particles, which underwent a more isotropic deformation, still exhibited an approximately round shape. Secondly, the influence of the surface structure on the mechanical properties of the compacts was studied. The indentation hardness and the tensile strength of compacts of microcrystalline cellulose (MCC) and anhydrous calcium phosphate (aCP) were studied. No differences were found for the compacts of MCC produced with the two kinds of punches, but the compacts of aCP obtained with uncovered punches presented a higher hardness and a higher tensile strength than those obtained with covered punches.

Characterization of archaeological burnt bones: contribution of a new analytical protocol based on derivative FTIR spectroscopy and curve fitting of the nu1nu3 PO4 domain.

Derivative Fourier transform infrared (FTIR) spectroscopy and curve fitting have been used to investigate the effect of a thermal treatment on the nu(1)nu(3) PO(4) domain of modern bones. This method was efficient for identifying mineral matter modifications during heating. In particular, the 961, 1022, 1061, and 1092 cm(-1) components show an important wavenumber shift between 120 and 700 degrees C, attributed to the decrease of the distortions induced by the removal of CO(3)(2-) and HPO(4)(2-) ions from the mineral lattice. The so-called 1030/1020 ratio was used to evaluate crystalline growth above 600 degrees C. The same analytical protocol was applied on Magdalenian fossil bones from the Bize-Tournal Cave (France). Although the band positions seem to have been affected by diagenetic processes, a wavenumber index--established by summing of the 961, 1022, and 1061 cm(-1) peak positions--discriminated heated bones better than the 1030/1020 ratio, and the splitting factor frequently used to identify burnt bones in an archaeological context. This study suggest that the combination of derivative and curve-fitting analysis may afford a sensitive evaluation of the maximum temperature reached, and thus contribute to the fossil-derived knowledge of human activities related to the use of fire.