Raguin Emeline, Rechav Katya, Shahar Ron, Weiner Steve
Department of Structural Biology, Weizmann Institute of Science, Rehovot, 76100, Israel.
Department of Chemical Research Support, Weizmann Institute of Science, Rehovot, Israel.
Acta Biomater. 2021 Feb;121:497-513. doi: 10.1016/j.actbio.2020.11.002. Epub 2020 Nov 18.
The mineralized collagen fibril is the basic building block of bone, and hence is the key to understanding bone structure and function. Here we report imaging of mineralized pig bone samples in 3D using the focused ion beam-scanning electron microscope (FIB-SEM) under conditions that reveal the 67 nm D-banding of mineralized collagen fibrils. We show that in adult pig osteons, the lamellar bone comprises alternating layers with either collagen fibrils predominantly aligned in one direction, and layers in which fibrils are predominantly aligned in two directions. The cement sheath contains thin layers of both these motifs, but its dominant structural component comprises a very complex layer of fibrils predominantly aligned in three or more directions. The degree of mineralization of the cement sheath is comparable to that of the osteon interior. The extent of alignment (dispersion) of the collagen fibrils in the osteonal lamellar bone is significantly higher than in the cement sheath. Canaliculi within the cement sheath are mainly aligned parallel to the cement sheath boundary, whereas in the lamellar bone they are mainly aligned perpendicular to the lamellar boundaries. This study further characterizes the presence of two types of collagen fibril arrangements previously identified in demineralized lamellar bone from other species. The simple sample preparation procedure for mineralized bone and the lower risk of introducing artifacts opens the possibility of using FIB-SEM to study more samples, to obtain automatic quantitative information on collagen fibril organization and to evaluate the degrees of mineralization all in relatively large volumes of bone.
矿化胶原纤维是骨骼的基本组成单位，因此是理解骨骼结构和功能的关键。在此，我们报告了在能揭示矿化胶原纤维67纳米D带的条件下，使用聚焦离子束扫描电子显微镜（FIB-SEM）对矿化猪骨样本进行三维成像的结果。我们发现，在成年猪的骨单位中，板层骨由交替的层组成，其中一层胶原纤维主要沿一个方向排列，另一层胶原纤维主要沿两个方向排列。骨水泥鞘包含这两种模式的薄层，但其主要结构成分是一层非常复杂的纤维层，主要沿三个或更多方向排列。骨水泥鞘的矿化程度与骨单位内部相当。骨单位板层骨中胶原纤维的排列（分散）程度明显高于骨水泥鞘。骨水泥鞘内的骨小管主要与骨水泥鞘边界平行排列，而在板层骨中，它们主要与板层边界垂直排列。本研究进一步表征了先前在其他物种脱矿板层骨中发现的两种胶原纤维排列类型的存在。矿化骨简单的样本制备程序以及引入伪像的风险较低，为使用FIB-SEM研究更多样本、获取有关胶原纤维组织的自动定量信息以及在相对较大体积的骨中评估矿化程度提供了可能性。
