Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, Research Campus Golm, 14424, Potsdam, Germany.
Mathematical Biophysics Group, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany.
Adv Mater. 2017 Jul;29(27). doi: 10.1002/adma.201701171. Epub 2017 May 9.
Teeth are designed to deliver high forces while withstanding the generated stresses. Aside from isolated mineral-free exception (e.g., marine polychaetes and squids), minerals are thought to be indispensable for tooth-hardening and durability. Here, the unmineralized teeth of the giant keyhole limpet (Megathura crenulata) are shown to attain a stiffness, which is twofold higher than any known organic biogenic structures. In these teeth, protein and chitin fibers establish a stiff compact outer shell enclosing a less compact core. The stiffness and its gradients emerge from a concerted interaction across multiple length-scales: packing of hydrophobic proteins and folding into secondary structures mediated by Ca and Mg together with a strong spatial control in the local fiber orientation. These results integrating nanoindentation, acoustic microscopy, and finite-element modeling for probing the tooth's mechanical properties, spatially resolved small- and wide-angle X-ray scattering for probing the material ordering on the micrometer scale, and energy-dispersive X-ray scattering combined with confocal Raman microscopy to study structural features on the molecular scale, reveal a nanocomposite structure hierarchically assembled to form a versatile damage-tolerant protein-based tooth, with a stiffness similar to mineralized mammalian bone, but without any mineral.
牙齿的设计目的是在承受产生的应力的同时传递高力。除了孤立的无矿物质例外（例如，海洋多毛类动物和鱿鱼），矿物质被认为是牙齿硬化和耐久性所必需的。在这里，展示了巨型钥匙孔贻贝（Megathura crenulata）的未矿化牙齿达到了刚度，是已知任何有机生物结构的两倍。在这些牙齿中，蛋白质和几丁质纤维形成了一个坚硬的外壳，外壳内部是一个不太紧凑的核心。这种刚度及其梯度是通过多种长度尺度的协同相互作用产生的：疏水性蛋白质的堆积和由 Ca 和 Mg 介导的二级结构折叠，以及在局部纤维方向上的强烈空间控制。这些结果结合了纳米压痕、声显微镜和有限元建模来探测牙齿的机械性能，利用小角和广角 X 射线散射来探测微米尺度上的材料有序性，以及与共聚焦拉曼显微镜结合的能量色散 X 射线散射来研究分子尺度上的结构特征，揭示了一种纳米复合材料结构，该结构以分层方式组装形成一种多功能的耐损伤蛋白质基牙齿，其刚度类似于矿化哺乳动物骨骼，但没有任何矿物质。
