Structural flexibility in the optical design of the arthopod cornea

节肢动物表皮是一种多功能的生物复合材料，由甲壳素纤维嵌入蛋白质基质中制成。角质层也形成了节肢动物复眼的角膜，这是该门的一个特征，在很大程度上有助于其令人难以置信的进化成功。在复眼结构中，每个感光单元（小眼）都有自己的光学元件。节肢动物的复眼是同源的，并显示出相似的一般结构。然而，特别是基本屈光单位经历了相当大的进化修改。在这里，我们建议研究在角膜角质层中观察到的不同结构的解决方案，所有这些都是成功的动物在各自的生活方式。目的是提高我们对角膜光学性能如何从其形状和底层几丁质结构中显现的理解。以前的大量工作集中在理解复眼光学与动物栖息地，昼夜适应，个体发育和进化适应的关系。更少的努力已经采取了理解角质层结构和甲壳素纤维组织和新兴的光学性能之间的基本关系。在我们的方法中，我们选择了三个物种：马蹄蟹，小龙虾和片脚类动物，我们表征其结构和组成，并监测角膜的光学和机械性能，利用合作小组内开发的各种先进技术。在鲎的小眼中，每个角膜都有一个圆锥状的突起，完全由几丁质角质层组成。相反，在下颌动物（多足动物、甲壳动物、六足动物）中，这一过程被细胞内的晶锥所取代，小眼角膜要么是豆状的，要么是光滑的，如所选的小龙虾和片足动物。角膜必须提供光学和机械功能，从而在这些约束之间调节结构。我们希望得出相关的几丁质结构，角质层组成的角膜和新兴的材料性能之间的相关性，以得出相关的结论，聚合物材料的设计。我们将利用合作伙伴在生物学表征和组织学方面的各种专业知识，以及诸如漫X射线散射和微衍射、拉曼光谱、低温电子显微镜等分析技术。这个建议的意义在于试图探索生物学中观察到的结构灵活性的边界，作为生物启发材料合成的设计策略的来源。

The arthropod cuticle is a versatile biocomposite made of chitin fibers embedded in a protein matrix. The cuticle also forms the cornea of the arthropod compound eye, a characteristic feature of the phylum that has largely contributed to its incredible evolutionary success. In the compound eye structure each photoreceptor unit (ommatidium) carries its own optics. Arthropod compound eyes are homologous and show a similar general structure. However, in particular the basic dioptric unit underwent considerable evolutionary modifications. Here we propose to study the different structural solutions observed in the cornea cuticle, all of which were successful for the animals in their respective lifestyle. The goal is to improve our understanding of how the corneas optical performance emerges from their shape and the underlying chitin architecture. A large body of previous work has focused on understanding the compound eye optics in relation to the animals habitat, diurnal adaptations, ontogeny and evolutionary adaptations. Much less effort has been taken to understand the fundamental relation between the cuticle structure and chitin fiber organization and the emerging optical properties. In our approach, we have selected three species: a horseshoe crab, a crayfish and an amphipod, and we characterize their structure and composition and monitor the optical and mechanical properties of the cornea exploiting diverse advanced techniques developed within the collaborating groups. In the ommatidia found in the horseshoe crab Limulus polyphemus (Chelicerata) each cornea possesses a cone-like process, made entirely of chitin-based cuticle. In the Mandibulata (myriapods, crustaceans, hexapods), in contrast, this process is replaced by an intracellular crystalline cone and the ommatidial cornea is either lentiform or smooth, as exemplified by the chosen crayfish and amphipod. The cornea has to serve both an optical and a mechanical function leading to adjusted structures between these constraints. We wish to draw correlations between the underlying chitin-structure, the cuticle composition of the cornea and the emerging materials properties in order to draw conclusions relevant for polymer materials design. We shall exploit the diverse expertise of the partners in biological characterization and histology, as well as analytical techniques such as diffuse X ray scattering and microdiffraction, Raman spectroscopy, cryo electron microscopy and more. The significance of this proposal is in the attempt to explore the boundaries of structural flexibility as observed in biology as a source of design strategies for bioinspired material synthesis.