Bone and teeth as fibrous biological composites: in situ nano-mechanical investigations

人造复合材料广泛应用于各种需要高强度和刚度以及低重量的结构中。这些复合材料几乎完全由纤维增强的轻质聚合物构成。该纤维具有优于其他几何形状的优点，因为在一个特定方向上的机械性能优异，使纤维各向异性。自然界中存在的众多结构通过进化过程被优化，以实现特定的机械功能。具有机械作用的生物材料的常见例子是骨骼系统中结构完整性所需的骨，以及主要用于咀嚼和撕裂食物的牙齿。这些材料与人造复合材料具有惊人的相似性，因为纤维成分被用作有机基质中的增强物。然而，与合成复合材料相比，生物复合材料中有两个主要差异是明显的。首先，生物复合材料中的增强纤维比工程复合材料中使用的典型纤维小得多。减小纤维直径被广泛认为可以增加强度，并且利用自然界中的尺度效应突出了所使用的优化过程。此外，许多组织水平存在于生物复合材料中，从增强纤维构建块的纳米级水平到大规模架构。这种结构层次目前比任何合成复合材料都要复杂得多。由于纤维增强材料的结构层次和小尺寸，了解纳米级纤维构建块如何影响生物复合材料的整体机械性能在实验上具有挑战性。由于纤维组织的多样性，对大样本进行的机械测试结果很难解释。因此，对生物复合材料中单个纳米级纤维增强材料的测试将提供基本信息，并有助于了解骨骼和牙齿等材料如何优化其机械功能。此外，对纳米级生物复合材料的理解可以为开发具有纳米材料增强的新型合成复合材料提供途径。该项目将测试牛骨股骨和帽贝牙齿样本，这些样本代表了自然界中发现的许多不同类型的骨骼和牙齿。纳米级纤维将通过拉伸这些纤维的末端进行机械测试。拉伸将通过扫描探针显微镜完成，这是测量变形和破坏纳米级纤维所需的非常小的力的理想选择。电子显微镜也将用于可视化这些测试，并观察纳米级纤维是否在拉伸过程中断裂或从周围的有机基质中滑出。传统复合材料理论中使用的力学模型将被应用于评估增强纳米纤维和周围有机基质的力学性能。因此，这项研究的结果将提供独特的见解，了解天然材料如何通过使用纳米尺度的构建块而具有显着的机械性能。

Man-made composite materials are used extensively in a variety of structures where high strength and stiffness is required as well as low weight. These composites are almost exclusively constructed from a lightweight polymer reinforced with fibres. The fibres have advantages over other geometries as the mechanical properties are excellent in one particular direction, making the fibre anisotropic. The numerous structures existing in nature are optimized through evolutionary processes for a particular mechanical function. Common examples of biological materials with a mechanical role are bone, required for structural integrity in skeletal systems, and teeth, primarily used for chewing and tearing of food. These materials have striking resemblances to man-made composites as fibrous constituents are used as reinforcement in an organic matrix. However, two main differences are apparent in biological composites when compared to synthetic composites. The first is that the reinforcing fibres in biological composites are much smaller than typical fibres used in engineering composites. Decreasing fibre diameter is widely acknowledged to increase strength and utilization of scale effects in nature highlights the optimization processes used. Furthermore, many organizational levels exist in biological composites from the nano-scale level of the reinforcing fibre building blocks up to the large scale architectures. This structural hierarchy is currently far more complex than any synthetic composite.Understanding how the nano-scale fibre building blocks influence the overall mechanical properties of the biological composite is experimentally challenging due to the structural hierarchy and small size of the fibre reinforcements. Mechanical tests on large samples give results that are difficult to interpret because of the various different fibre organizations. Therefore, testing on the individual nano-scale fibre reinforcements in biological composites would give fundamental information and help to understand how materials like bone and teeth are optimized for their mechanical functions. In addition, the understanding of biological composites at the nano-scale could provide a pathway for developing new synthetic composites with nano-material reinforcements.The project will test samples of bovine bone femur and limpet teeth, which are representative of many different types of bone and teeth found in nature. The nano-scale fibres will be mechanical tested by pulling at the ends of these fibres. The pulling will be done by a scanning probe microscopy, which is ideal for measuring the very small forces needed to deform and break the nano-scale fibres. An electron microscope will also be used to visualize these tests and observe if the nano-scale fibres are fractured during the pulling process or slide out of the surrounding organic matrix. Mechanical models used in conventional composite theory will be applied to assess the mechanical properties of the reinforcing nano-fibres and the surrounding organic matrix. The results of this research will therefore provide unique insight into how natural materials have remarkable mechanical properties from using nano-scale building blocks.