Correlation Between Texture of Hydroxyapatite and Mechanical Anisotropy in Loxodonta Africana Ivory

Abstract

Samples of Loxodonta africana ivory were subjected to X-ray diffraction studies which showed that the hexagonal crystals have a strong preferred orientation with their basal planes perpendicular to the longitudinal axis of the tusk. Cylindrical samples were also machined from the tusk with cylinder axes along and perpendicular to the longitudinal axis of the tusk respectively. Three-point bending tests were performed on the cylindrical samples. The results show a clear anisotropy in the bending strength along the two directions. The sample with cylindrical axis longitudinally aligned shows less bending for the same applied force. The results verify a correlation between orientation of hydroxyapatite and, among other things, the mechanical strength. This may be related to the function of the tusk which with normal usage has to be able to sustain large bending forces in a direction normal to the longitudinal axis.

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

“…Previous studies showed that elephant tusks present anisotropic mechanical properties (hardness, plastic deformation, bending and tensile strength and toughness) [27,36,37,49,50]. Here, we attempt to relate the ivory MCF particular organization to some of these mechanical properties and further compare it to those of teeth dentin, antler and bone in terms of mechanical properties and functions.…”

“…However, MCF orientation in 3D can be very different. MCF in ivory have preferential orientation along the tusk axis [26,27,37] and are arranged in an oscillating plywood structure [this study], whereas MCF in the coronal dentin are mainly randomly oriented within the mineralization plane [13,52]. The latter is repeatedly loaded in compression, whereas elephant tusks are rather loaded in bending [37] due to their elongated shape (up to 3.5 m long), important weight (up to 117 kg) [14] and their function of carrying loads.…”

“…Finally, at the nanoscale, ivory is composed of staggered collagen molecules and Mg-rich carbonated hydroxyapatite nano-crystals (Mg-carb-HAP) constituting the mineralized fibrils that are together arranged into the MCF [19,[26][27][28][29]. As for many other biological materials [10,[30][31][32][33][34], the mechanical properties of elephant ivory [27,[35][36][37] originate from its nano-composite nature and hierarchical structure from macro-down to nanoscale.…”

Informative Potential of Multiscale Observations in Archaeological Biominerals Down to Nanoscale

“…Cui et al (1994) investigated the orientation dependence of indentation morphology and micro-hardness of ivory (Cui et al 1994). Nothnagel et al (1996) correlated the texture of hydroxyapatite and mechanical properties related to the function of the tusk (Nothnagel et al 1996). The correlation between the orientation of the collagen fibers and the elastic properties was shown by Nalla et al (2003) for elephant ivory and by Currey et al (1994) for narwhal ivory (Nalla 2003;Currey et al 1994).…”

Central Sclerit Forms of Baikal Omul Scale and its Intraspecies Variability

“…Взаимодействуя с коллагеновым волокном, биогенный гидроксилапатит, в свою очередь, образует шести-, пяти-, четырёхгранные фигуры (Nothnagel et al, 1996).…”