Department of Mechanical Engineering, University of Washington, Seattle, WA, 98195, USA.
Department of Materials Science and Engineering, University of Washington, Seattle, WA, 98195, USA.
J Mech Behav Biomed Mater. 2022 Aug;132:105299. doi: 10.1016/j.jmbbm.2022.105299. Epub 2022 May 30.
The exoskeletons of crustaceans are essential for providing protection from predators and other environmental threats. Understanding the structure and mechanical behavior of their natural armor could inspire the design of lightweight and high toughness synthetic materials. Most published work has focused on marine crustacea rather than their terrestrial counterparts, which are exposed to a multitude of unique threats. The interest in the terrestrial isopod Armadillidium vulgare (A. vulgare) has grown but the interrelationship between the microstructure, chemical composition, and mechanical properties has not been thoroughly investigated. Thus, this study aims to elucidate missing details concerning this biological mineralized composite. Exoskeleton specimens were fixated to preserve the intrinsic protein structure. We utilize scanning electron microscopy for microstructure analysis, Raman spectroscopy for elemental analysis, and nanoindentation property mapping to achieve mechanical characterization. The naturally fractured A. vulgare exoskeleton cross-section reveals four subregions with the repeating helicoidal 'Bouligand' arrangement most prominent in the endocuticle. The hardness and reduced modulus distributions exhibit a through-thickness exponential gradient with decreasing magnitudes from the outermost to the innermost layers of the exoskeleton. The Raman spectra show a graded spatial distribution of key constituents such as calcium carbonate across the thickness, some of which are consistent with the mechanical property gradient. Potential microstructure, elemental composition, and mechanical property relationships are discussed to explain how the hierarchical structure of this nanolaminate armor protects this species.
甲壳动物的外骨骼对于提供对捕食者和其他环境威胁的保护至关重要。了解其天然盔甲的结构和机械性能可以启发设计出轻量且高韧性的合成材料。大多数已发表的工作都集中在海洋甲壳类动物上，而不是它们的陆地对应物，这些陆地对应物面临着多种独特的威胁。对陆地等足目动物 Armadillidium vulgare (A. vulgare) 的兴趣日益增加，但微观结构、化学成分和机械性能之间的相互关系尚未得到彻底研究。因此，本研究旨在阐明有关这种生物矿化复合材料的缺失细节。外骨骼标本被固定以保留内在的蛋白质结构。我们利用扫描电子显微镜进行微观结构分析、拉曼光谱进行元素分析以及纳米压痕特性映射来实现机械特性表征。天然断裂的 A. vulgare 外骨骼横截面显示出四个亚区，其中螺旋状的“Bouligand”排列在最突出的内表皮中。硬度和降低的模量分布呈现出贯穿厚度的指数梯度，从外骨骼的最外层到最内层逐渐减小。拉曼光谱显示出关键成分（如碳酸钙）在厚度上的分级空间分布，其中一些与机械性能梯度一致。讨论了潜在的微观结构、元素组成和机械性能关系，以解释这种纳米层状盔甲的分层结构如何保护该物种。
