Dissolution of cortical bone mineral under demineralization in 0.1 M HCl and 0.1 M EDTA solutions is studied by X-ray diffraction (XRD). The bone specimens (in the form of planar oriented pieces) were cut from a diaphysial fragment of a mature mammal bone so that a cross-section surface and a longitudinal section surface could be analyzed individually. This permitted to compare the dissolution behavior of bone apatite of different morphologies: crystals having the c-axis of the hexagonal unit-cell generally parallel to the long axis of the bone (major morphology) and those having the c-axis almost perpendicular to the bone axis (minor morphology). For these two types of morphology, the crystallite sizes in two mutually perpendicular directions (namely, [002] and [310]) were estimated by Scherrer formula in the initial and the stepwise-demineralized specimens. The data obtained reveal that the crystals belonging to the minor morphology dissolve faster than the crystals of the major morphological type, despite the fact that the crystallites of the minor morphology seem to be only a little smaller than those of the major morphology; the apatite crystallites irrespective of the morphology type are elongated in the c-axis direction. We hypothesize that the revealed difference in solubility may be caused by diverse chemical modifications of apatite of these two morphological types, since the solubility of apatite is strictly regulated by anionic and cationic substitutions in the lattice. The anisotropy effect in solubility of bone mineral seems to be functionally predetermined and this should be a crucial factor in the resorption and remodeling behavior of a bone. Some challenges arising at XRD examination of partially decalcified cortical bone blocks are discussed, as well as the limitations of estimation of bone crystallite size by XRD line-broadening analysis.

中文翻译：

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XRD 分析揭示了皮质骨脱矿质溶解行为的各向异性方面

通过 X 射线衍射 (XRD) 研究了皮质骨矿物质在 0.1 M HCl 和 0.1 M EDTA 溶液中脱矿质的溶解。从成熟哺乳动物骨的骨干碎片中切下骨标本（以平面定向块的形式），以便可以单独分析横截面表面和纵向截面表面。这允许比较不同形态的骨磷灰石的溶解行为：六方晶胞的 c 轴通常平行于骨长轴（主要形态）的晶体和 c 轴几乎垂直于骨长轴的晶体。骨轴（次要形态）。对于这两种形态，微晶尺寸在两个相互垂直的方向（即，[002] 和 [310]) 在初始和逐步脱矿的样品中通过 Scherrer 公式估计。获得的数据表明，属于次要形态的晶体比主要形态类型的晶体溶解得更快，尽管次要形态的微晶似乎只比主要形态的微晶小一点；无论形态类型如何，磷灰石微晶都在 c 轴方向上被拉长。我们假设溶解度的显着差异可能是由这两种形态类型的磷灰石的不同化学修饰引起的，因为磷灰石的溶解度受到晶格中阴离子和阳离子取代的严格调节。骨矿物质溶解度的各向异性效应似乎在功能上是预先确定的，这应该是骨吸收和重塑行为的关键因素。讨论了部分脱钙皮质骨块的 XRD 检查中出现的一些挑战，以及通过 XRD 线加宽分析估计骨微晶大小的局限性。