Institute of Biophysics, University of Natural Resources and Life Sciences Vienna, Vienna, 1190, Austria.
Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, Potsdam-Golm, 14476, Germany.
Adv Mater. 2020 Dec;32(48):e2004519. doi: 10.1002/adma.202004519. Epub 2020 Oct 20.
Many organisms encapsulate their embryos in hard, protective shells. While birds and reptiles largely rely on mineralized shells, plants often develop highly robust lignocellulosic shells. Despite the abundance of hard plant shells, particularly nutshells, it remains unclear which fundamental properties drive their mechanical stability. This multiscale analysis of six prominent (nut)shells (pine, pistachio, walnut, pecan, hazelnut, and macadamia) reveals geometric and structural strengthening mechanisms on the cellular and macroscopic length scales. The strongest tissues, found in walnut and pistachio, exploit the topological interlocking of 3D-puzzle cells and thereby outperform the fiber-reinforced structure of macadamia under tensile and compressive loading. On the macroscopic scale, strengthening occurs via an increased shell thickness, spherical shape, small size, and a lack of extended sutures. These functional interrelations suggest that simple geometric modifications are a powerful and resource-efficient strategy for plants to enhance the fracture resistance of entire shells and their tissues. Understanding the interplay between structure, geometry, and mechanics in hard plant shells provides new perspectives on the evolutionary diversification of hard seed coats, as well as insights for nutshell-based material applications.
许多生物将胚胎包裹在坚硬的保护壳中。虽然鸟类和爬行动物主要依赖于矿化的外壳，但植物通常会形成高度坚固的木质纤维素外壳。尽管硬壳植物（尤其是坚果壳）的数量丰富，但仍不清楚哪些基本特性决定了它们的机械稳定性。本研究对六种突出的（坚果）壳（松、开心果、胡桃、山核桃、榛子和澳洲坚果）进行了多尺度分析，揭示了细胞和宏观尺度上的几何和结构强化机制。在核桃和开心果中发现的最强组织利用了 3D 拼图细胞的拓扑互锁，从而在拉伸和压缩载荷下优于澳洲坚果的纤维增强结构。在宏观尺度上，通过增加壳厚度、球形形状、减小尺寸和减少扩展缝合线来实现强化。这些功能关系表明，简单的几何修改是植物增强整个外壳及其组织抗断裂能力的一种强大且高效的策略。了解坚硬植物外壳中的结构、几何形状和力学之间的相互作用，为坚硬种皮的进化多样化提供了新的视角，并为基于坚果壳的材料应用提供了新的见解。
