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The three-dimensional arrangement of the mineralized collagen fibers in elephant ivory and its relation to mechanical and optical properties
Acta Biomaterialia ( IF 9.7 ) Pub Date : 2018-03-01 , DOI: 10.1016/j.actbio.2018.02.016
M. Albéric , A. Gourrier , W. Wagermaier , P. Fratzl , I. Reiche

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 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.



中文翻译:

象牙中矿化胶原纤维的三维排列及其与机械和光学性能的关系

象牙由牙本质或象牙组成,牙本质或象牙是由矿化胶原纤维(MCF)制成的一种层次化的复合生物材料。据信MCF的具体安排负责for牙的光学和机械性能。尤其是MCF组织可能有助于在象牙的抛光部分上观察到明亮和黑暗的棋盘图案(Schreger图案)。然而,这种光学图案的确切结构起源仍是有争议的。我们在此使用象牙样品的互补分析方法(小角度和广角X射线散射,交叉偏振光显微镜和扫描电子显微镜)解决此问题,并表明象牙的MCF取向从其外部到内部各不相同。象牙。MCF的外部粘合层的纤维方向垂直于象牙轴,包裹了中齿质区域,其中MCF主要沿象牙轴定向,并以胶合板状结构排列,纤维定向在狭窄的角度范围内振荡。MCF的这种特殊的振荡胶合板结构和胶原纤维的双折射特性,可能有助于Schreger模式的出现,Schreger模式是在矿化组织中观察到的最引人入胜的宏观光学模式之一,对于考古学和考古学中的认证问题非常重要。法医科学。

重要声明

象牙是有趣的生物材料,因为它们由像牙齿的牙本质(象牙)组成,但具有矿化的胶原纤维(MCF),其与片状骨骼的排列相似,具有骨骼或鹿角的功能。在这里,我们显示出象牙具有渐变的结构,其MCF方向不同,并且中齿质的MCF排列成胶合板状的层,纤维方向围绕象牙轴在狭窄的角度范围内振荡。MCF的这种组织结构可能有助于提高象牙的机械性能,并与胶原纤维的双折射性能密切相关,这与它的光学性能有关,即出现了宏观的棋盘图案(众所周知的Schreger图案)。

更新日期:2018-03-02
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