Department of Chemical Engineering and Chemistry, Laboratory of Materials and Interface Chemistry and Center for Multiscale Electron Microscopy, Eindhoven University of Technology, PO Box 513, 5600 MB, Eindhoven, The Netherlands.
Institute for Complex Molecular Systems, Eindhoven University of Technology, PO Box 513, 5600 MB, Eindhoven, The Netherlands.
Nat Commun. 2020 Oct 8;11(1):5068. doi: 10.1038/s41467-020-18846-2.
The mineralized collagen fibril is the basic building block of bone, and is commonly pictured as a parallel array of ultrathin carbonated hydroxyapatite (HAp) platelets distributed throughout the collagen. This orientation is often attributed to an epitaxial relationship between the HAp and collagen molecules inside 2D voids within the fibril. Although recent studies have questioned this model, the structural relationship between the collagen matrix and HAp, and the mechanisms by which collagen directs mineralization remain unclear. Here, we use XRD to reveal that the voids in the collagen are in fact cylindrical pores with diameters of ~2 nm, while electron microscopy shows that the HAp crystals in bone are only uniaxially oriented with respect to the collagen. From in vitro mineralization studies with HAp, CaCO and γ-FeOOH we conclude that confinement within these pores, together with the anisotropic growth of HAp, dictates the orientation of HAp crystals within the collagen fibril.
矿化胶原纤维是骨骼的基本组成部分，通常被描绘为贯穿胶原的超薄碳酸羟基磷灰石 (HAp) 薄片的平行排列。这种取向通常归因于纤维内二维空隙中 HAp 和胶原分子之间的外延关系。尽管最近的研究对该模型提出了质疑，但胶原基质和 HAp 之间的结构关系以及胶原指导矿化的机制仍不清楚。在这里，我们使用 XRD 揭示了胶原中的空隙实际上是直径约为 2nm 的圆柱形孔，而电子显微镜显示骨中的 HAp 晶体仅相对于胶原单轴取向。通过对 HAp、CaCO 和 γ-FeOOH 的体外矿化研究，我们得出结论，这些孔内的限制以及 HAp 的各向异性生长决定了 HAp 晶体在胶原纤维内的取向。
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