Abstract
Aiming to understand Nature´s strategies that inspire new composite materials, the hierarchical levels of organization of the Brazil nut (Bertholletia excelsa) mesocarp were investigated. Optical microscopy, scanning electron microscopy (SEM), microtomography (MicroCT) and small-angle X-ray scattering (SAXS) were used to deeply describe the cellular and fibrillary levels of organization. The mesocarp is the middle layer of the fruit which has developed several strategies to avoid its opening and protect its seed. Fibers have a different orientation in the three layers of the mesocarp, what reduces the anisotropy of the structure. Sclereids cells with thick cell walls fill the spaces between the fibers resembling a foam-filled structural composite. The mesocarp has several tubular channels and fractured surfaces which may work as sites for crack trapping and increase toughness. The thick and lignified cell wall of sclereids and fibers and the weak interface between cells can promote a longer and tortuous intercellular crack path. Additionally, fibers with high strength and stiffness due to microfibrils oriented along the main cell axis (µ = 0° to 17°) were identified in the innermost layer of the mesocarp. Such an understanding of each hierarchical level can inspire the development of new cellular composites with improved mechanical behavior
Highlights
Aiming to understand Natures strategies that inspire new composite materials, the hierarchical levels of organization of the Brazil nut (Bertholletia excelsa) mesocarp were investigated
The presence of hollow and empty cells is a well-known strategy of Nature to simultaneously optimize stiffness, strength and overall weight[16]
As the mesocarp only has dead cells after maturation, the transport of nutrients is useless for the mature fruit, the phloem cells can be absorbed by mesocarp leaving hollow channels behind
Summary
Aiming to understand Natures strategies that inspire new composite materials, the hierarchical levels of organization of the Brazil nut (Bertholletia excelsa) mesocarp were investigated. Fibers with high strength and stiffness due to microfibrils oriented along the main cell axis (μ = 0° to 17°) were identified in the innermost layer of the mesocarp Such an understanding of each hierarchical level can inspire the development of new cellular composites with improved mechanical behavior. On the largest length-scale, the “macroscopic” level, trunk, leaves, roots, flowers, and fruit are distinguished, and it is analyzed how the association of different tissues leads to different geometries and functions in the plant. At this level, the mesocarp is described as a spherical or elliptical shell of 10–12 cm diameter with a wall thickness of approximately 1 cm. The main vegetable tissues are parenchyma, collenchyma, sclerenchyma, and vascular system; within these, cells are classified regarding their morphology, wall thickness, composition, and function
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