The Puzzle of the Walnut Shell: A Novel Cell Type with Interlocked Packing

The outer protective shells of nuts can have remarkable toughness and strength, which are typically achieved by a layered arrangement of sclerenchyma cells and fibers with a polygonal form. Here, the tissue structure of walnut shells is analyzed in depth, revealing that the shells consist of a singl...

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Bibliographic Details
Published in:Advanced science 2019-08, Vol.6 (16), p.1900644-n/a
Main Authors: Antreich, Sebastian J., Xiao, Nannan, Huss, Jessica C., Horbelt, Nils, Eder, Michaela, Weinkamer, Richard, Gierlinger, Notburga
Format: Article
Language:English
Subjects:
3D structures
Communication
Communications
interlocked packing
Microscopy
puzzle cells
sclereids
Seeds
walnut shell
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Summary:The outer protective shells of nuts can have remarkable toughness and strength, which are typically achieved by a layered arrangement of sclerenchyma cells and fibers with a polygonal form. Here, the tissue structure of walnut shells is analyzed in depth, revealing that the shells consist of a single, never reported cell type: the polylobate sclereid cells. These irregularly lobed cells with concave and convex parts are on average interlocked with 14 neighboring cells. The result is an intricate arrangement that cannot be disassembled when conceived as a 3D puzzle. Mechanical testing reveals a significantly higher ultimate tensile strength of the interlocked walnut cell tissue compared to the sclerenchyma tissue of a pine seed coat lacking the lobed cell structure. The higher strength value of the walnut shell is explained by the observation that the crack cannot simply detach intact cells but has to cut through the lobes due to the interlocking. Understanding the identified nutshell structure and its development will inspire biomimetic material design and packaging concepts. Furthermore, these unique unit cells might be of special interest for utilizing nutshells in terms of food waste valorization, considering that walnuts are the most widespread tree nuts in the world. Walnut shells consist of a single, previously unreported, cell type—the polylobate 3D sclereid cells—which intricately interlock all neighboring cells. This novel cell type is described and discussed in detail by considering the structural changes during nutshell maturation and the mechanical implications that arise from their 3D puzzle shape.
ISSN:2198-3844
2198-3844
DOI:10.1002/advs.201900644