P3 - Fishbone: Bones without cells as blueprints for durable, cyclically loaded nanocomposites: how does anosteocytic fishbone cope with fatigue?

对于哺乳动物的骨骼，人们普遍认为骨细胞感知应变并启动疲劳损伤的重塑和修复。但高级硬骨鱼的骨骼缺乏骨细胞。他们如何维持数百万次的加载周期？这种坚韧和耐疲劳的材料为生物启发的复合材料提供了一个理想的角色模型。在这个项目中，我们阐明了哪些结构实体和哪些长度的鳞片上的结构实体主导着无骨细胞鱼骨的疲劳性能，以及它们是如何相互作用的，并与细胞鱼骨进行了比较。成分、纤维取向和孔隙率将通过组织学/材料学定量评估，重点是3D高分辨率调查。重点将放在识别预先存在的微裂纹、纳米/微米级孔隙率和纳米级残余应力上。基于全骨微计算机断层扫描数据的有限元建模将有助于我们与基于数字图像相关性的应变数据相结合，更好地了解几何、宏观孔隙率、应力/应变分布和活体载荷条件之间的关系。我们将把被确认为对有机-无机复合材料的抗疲劳性能很重要的结构特征转移到有机-无机复合材料上，同时改变它们的相对数量，跨越长度尺度，并通过组合不同的加工路线。这将涉及了解复合加工对有机结构和有机/无机界面的影响。通过熔融电写(MEW)、静电纺丝以及它们的组合，可以从天然或合成的有机前驱体中制备出具有纳米或微米级直径(以研究分级结构)和不同硬度的复合纤维。通过使用不同的晶体形状，考虑各向异性的影响，使用/不使用羟基磷灰石(HA)纳米颗粒来制备不同宏观几何形状的MEW支架，以提高疲劳性能。三明治结构将通过用纳米纤维支撑这些宏观结构来获得，其中包含/不包含HA纳米颗粒。所有的结构都将根据它们的物理和化学性质进行研究。所有试验都是在模拟体液中进行的，考虑了保持时间和频率变化对粘弹性变形的影响。疲劳引起的结构变化将在2D/3D中进行研究，至于卸载状态。从中等矿化度的生物材料的角度来看，我们将通过提供关于成分如何影响疲劳抗力的知识，以及如何用最少的人工制品来测试纳米复合材料，从而为形成做出贡献。

For mammalian bone, it is widely accepted that osteocyte cells sense strains and initiate remodelling and repair of fatigue-damage. But bone of advanced teleost fish lacks osteocytes. How do they sustain millions of loading cycles? This tough and fatigue resistant material presents an ideal role model for bioinspired composites.In this project we elucidate which structural entities on which length scales dominate fatigue resistance of anosteocytic fishbone and how they interact, in comparison with cellular fishbone. Composition, fibre orientation and porosity will be evaluated quantitatively by histology/materialography, with an emphasis on 3D high resolution investigations. A focus will be on identfying pre-existing micro-cracks, nano-/ microscale porosity, and nm-sized residual stresses. Finite element modelling, based on whole bone microcomputed tomography data, will help us, in synergy with strain data based on digital image correlation to better understand connections between geometry, macro-porosity, stress/strain distributions and in vivo loading conditions. We will transfer structural features identified as important for the fatigue resistance to organic-inorganic composites, while modifying their relative amount, across length scales and by combining different processing routes. This will involve understanding the impact of composite processing on the organic structure and the organic/inorganic interfaces. Composite fibers with nano- or microscale diameters (to investigate hierarchical structures) and different stiffness will be made by melt electrowriting (MEW), electrospinning, and their combination from natural or synthetic organic precursors. MEW scaffolds with different macro-geometries will be produced with/without hydroxyapatite (HA) nanoparticles to enhance fatigue properties, considering effects of anisotropy by using different crystal shapes. Sandwich structures will be obtained by supporting these macrostructures with nanofibers with/without incorporated HA nanoparticles. All structures will be investigated in terms of their physical and chemical properties. All tests are performed in simulated body fluid, considering viscoelastic deformation by holding times and frequency variations. Fatigue-induced structural changes will be investigated in 2D/3D, as for the unloaded state. From the viewpoint of a biological material with intermediate mineralization degree, we will contribute to the FOR by providing knowledge on how composition affects fatigue resistance, and how the nanocomposites can be tested with minimum of artefacts.