Crustacean skeletal elements: variations in the constructional morphology at different hierarchical levels

甲壳类动物的角质层是一种分层组织的复合材料，覆盖整个动物，形成连续的外骨骼。角质层的有机阶段至少有七个层次。它由几丁质分子组成，形成被蛋白质包裹的结晶原纤维。这些原纤维形成平面，堆叠在扭曲的胶合板结构中，构成角质层四个主要层中的三个。其中至少两种，即外膜和内膜，含有矿物相，主要是镁方解石、无定形碳酸钙（ACC）和磷酸盐（ACP）。高数量的层次和成分多样性为改变材料的物理，特别是机械性能提供了高度的自由度。这使得角质层成为一种多功能材料，非常适合形成各种骨骼元素，适应不同的功能和个体物种的生态生理菌株。在我们的比较方法中，我们结合实验和数学方法来研究如何以及在哪些层次结构和成分被修改以达到所需的物理性质。利用这些研究积累的知识，我们建立了一个从分子到宏观尺度系统描述角质层复合材料结构-组成-性能关系的理论模型。我们多学科项目的目标是在基于知识的设计方法中促进优化仿生材料的开发。

The crustacean cuticle is a hierarchically organized composite material that covers the whole animal and forms the continuous exoskeleton. The organic phase of the cuticle is organized in at least seven hierarchical levels. It consists of chitin molecules forming crystalline fibrils enveloped by proteins. These fibrils form planes that are stacked in a twisted plywood structure constituting three of the cuticle´s four principal layers. At least two of them, the exo- and endocuticle, contain a mineral phase of mainly Mg-calcite, amorphous calcium carbonate (ACC) and phosphate (ACP). The high number of hierarchical levels and the compositional diversity provide a high degree of freedom for varying the physical, in particular mechanical, properties of the material. This makes the cuticle a versatile material ideally suited to form a variety of skeletal elements that are adapted to different functions and the eco-physiological strains of individual species. In our comparative approach, we combine experimental and mathematical methods to investigate how, and at which hierarchical levels structure and composition are modified to achieve the required physical properties. Using the accumulated knowledge from these studies, we develop a theoretical model that systematically describes the structure-composition-property relations of cuticle composites from the molecular to the macro-scale. The goal of our multidisciplinary project is to facilitate the development of optimized biomimetic materials within a knowledge-based design approach.