P2 “Enamel”: Natural enamel and water-glass based composites – decoding structure-function relationship regarding fatigue resistance of two complementary systems

牙釉质是人体内最坚硬的物质，是牙齿最外层的保护层。它有一个复杂的层次结构，基于95%的羟基磷灰石（HA）纳米纤维晶体捆绑在不同方向的棒上。少量的有机基质积聚在低矿物密度的地方，例如晶体和棱镜之间。天然牙釉质的微纳米结构和无机纳米晶体在低含量有机基质中的排列显著有助于出色的抗疲劳性能，从而实现终身功能。然而，在一定条件下，裂纹的形成和扩展会影响和破坏天然牙釉质。然而，对牙釉质的长时间疲劳行为知之甚少。硅酸钠溶液（“水玻璃”，WG）是一种多功能的无机材料，具有可调的（粘）弹性性能。它的化学性质和可调节的含水量允许通过各种加工路线制造WG基复合材料。与（生物）聚合物结合，WG可用于加工具有不同矿物含量的有机-无机模型结构。因此，受珐琅复杂的纤维基复合结构的启发，它是纳米复合材料的理想前体。该项目的目的是将天然珐琅建筑转化为基于WG的复合结构，从纳米到宏观尺度，同时利用WG加工的多功能性。我们将结合3d打印，静电纺丝和电子书写技术，以达到多功能的新型加工路线。定制聚合物和无机相之间的界面将进一步受到牙科应用和无机材料的经验的启发。这将是一项资产，也有助于其他FOR项目。通过研究天然牙釉质和wg基复合材料的疲劳行为和耐疲劳性，我们将确定以类似或不同的方式促进抗疲劳性的结构策略和特征，以及这如何影响寿命。为了了解分层纳米和微观结构对牙釉质和二维和三维钨基复合材料长期抗疲劳性能的相对贡献，我们将在咀嚼模拟器上进行宏观试件的疲劳测试，并在中央疲劳实验室进行微纳米尺度的循环纳米压痕疲劳测试。整个项目的重要方面是水的含量和温度，影响wg基复合材料的加工和性能，以及水的含量，环境介质的组成和温度在试样制备和两种材料组试样的疲劳试验期间。因此，与其他FOR成员一起，我们将为开发可靠的生物和仿生纳米复合材料的试样制备和疲劳测试程序做出贡献。

Enamel is the hardest material in the human body and forms the outermost protection of teeth. It has a complex hierarchical structure based on 95% hydroxyapatite (HA) nanofiber crystallites bundled to rods that are oriented into different directions. A small amount of organic matrix accumulates at sites of low mineral density, e.g. between crystals and prisms. The micro- and nanoarchitecture of natural tooth enamel and the arrangement of inorganic nanocrystals in a low amount of organic matrix contribute significantly to the outstanding fatigue resistance that enables lifelong function. Nevertheless, under certain conditions, crack formation and propagation can affect and damage the natural tooth enamel. Little is known, however, about the long-time fatigue behavior of enamel. Sodium-silicate solution (“water-glass”, WG), is a versatile, inorganic material with tuneable (visco-)elastic properties. Its chemistry and the adjustable water content allow manufacturing of WG based composites by a variety of processing routes. In combination with (bio-) polymers WG can be used to process organic-inorganic model structures with varying mineral content. It is therefore an ideal precursor for nanocomposites inspired by the complex fiber-based composite structure of enamel. The aim of this project is to transfer natural enamel architecture to WG-based composite structures, from the nano- to the macro-scale, while exploiting the versatility of WG processing. We will combine 3D-printing, electrospinning and electro-writing techniques to reach versatile novel processing routes. Tailoring the interface between the polymer and inorganic phases will further be inspired by the experience from dental applications and inorganic materials. This will be an asset contributing also to the other FOR projects. By investigating fatigue behavior and resistance of natural enamel and WG-based composites we will identify structural strategies and features that contribute to fatigue resistance in a similar or different way and how this affects longevity. To understand the relative contribution of the hierarchical nano- and microstructure on the long-time fatigue resistance of enamel and of 2D and 3D WG-based composites, we will perform fatigue tests on macro-specimens in a chewing simulator, and on the micro- and nanoscale with cyclic nanoindentation in the central fatigue lab. Important facets throughout the project are water content and temperature, influencing processing and properties of the WG-based composites, as well as water content, composition of the environmental medium and temperature during specimen preparation and fatigue testing of specimens of both material groups. Thus, together with the other FOR members, we will contribute to develope reliable specimen preparation and fatigue testing procedures for biological and bio-inspired nanocomposites.