The proportion of bark in tree trunks is in the range of ~ 10-20%. This large amount of material is currently mainly considered as a by- or even waste-product by the timber processing industry. ...Recently, efforts towards the use of bark have been made, e.g. as a raw material to harvest different chemical compounds or as an additive for wood particle boards. Our motivation for this work was to keep the bark in an almost natural state and explore alternative processes and applications for use. The traditional method of de-barking tree trunks by peeling was used to harvest large bark pieces. Two pieces of peeled bark were placed crosswise, with the rhytidom side (outer bark) facing each other. After different conditioning steps, bark pieces were hot pressed to panels without adding adhesives. These experiments on bark samples of different Central European tree species suggest that production of panels with species dependent properties is possible and feasible. This is a step towards producing sustainable panels by using a natural waste material, while retaining its beneficial structure and its natural chemical composition.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Isolated single wood fibres with cellulose fibril angles from 10 to 43° were tested in microtensile tests under controlled temperature and relative humidity of 5, 50, 75, 90% and in the wet state. ...This systematic study provides experimental stiffness and strength data, calculated on cell wall cross sections. It has been shown that stiffness reduction with increasing moisture content is more pronounced in fibres with large cellulose fibril angles. Interestingly, stiffness reduction in fibres with low cellulose fibril angles has been observed for the fully hydrated state only. The experimental dataset was fed into a model to determine moisture dependent stiffness of the hemicellulose-lignin-matrix and the stresses acting on the fibrils and the matrix.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
During bone formation, collagen fibrils mineralize with carbonated hydroxyapatite, leading to a hybrid material with excellent properties. Other minerals are also known to nucleate within collagen in ...vitro. For a series of strontium- and calcium-based minerals, we observed that their precipitation leads to a contraction of collagen fibrils, reaching stresses as large as several megapascals. The magnitude of the stress depends on the type and amount of mineral. Using in-operando synchrotron x-ray scattering, we analyzed the kinetics of mineral deposition. Whereas no contraction occurs when the mineral deposits outside fibrils only, intrafibrillar mineralization generates fibril contraction. This chemomechanical effect occurs with collagen fully immersed in water and generates a mineral-collagen composite with tensile fibers, reminiscent of the principle of reinforced concrete.
Zebra and quagga mussels (
) are invasive freshwater biofoulers that perpetrate devastating economic and ecological impact. Their success depends on their ability to anchor onto substrates with ...protein-based fibers known as byssal threads. Yet, compared to other mussel lineages, little is understood about the proteins comprising their fibers or their evolutionary history. Here, we investigated the hierarchical protein structure of
byssal threads and the process by which they are fabricated. Unique among bivalves, we found that threads possess a predominantly
-sheet crystalline structure reminiscent of spider silk. Further analysis revealed unexpectedly that the
thread protein precursors are mechanoresponsive
-helical proteins that are mechanically processed into
-crystallites during thread formation. Proteomic analysis of the byssus secretory organ and byssus fibers revealed a family of ultrahigh molecular weight (354 to 467 kDa) asparagine-rich (19 to 20%) protein precursors predicted to form
-helical coiled coils. Moreover, several independent lines of evidence indicate that the ancestral predecessor of these proteins was likely acquired via horizontal gene transfer. This chance evolutionary event that transpired at least 12 Mya has endowed
with a distinctive and effective fiber formation mechanism, contributing significantly to their success as invasive species and possibly, inspiring new materials design.
The mucilaginous viscin tissue within mistletoe berries possesses an extraordinary ability to be rapidly processed under ambient conditions into stiff cellulosic fibers (>14 GPa) through simple ...mechanical drawing. This rapid and extreme transformation process is hydration-dependent and involves an astonishing >200-fold increase in length, providing a relevant role model for efforts to produce advanced composites from cellulose-based structures such as cellulose nanocrystals or cellulose nanofibrils. Using a combination of in situ polarized light microscopy, synchrotron X-ray scattering, and humidity-controlled mechanical analysis, we examine here the dynamic transition of a viscin cell bundle from hydrogel-like tissues to high-performance fibers. Our findings indicate a massive phase transition in which cellulose microfibrils containing high-aspect-ratio crystalline domains undergo dramatic reorganization, facilitated by a water-responsive noncellulosic matrix. Transition from an aligned, yet flowing state to a stiff fiber is likely triggered by rapid water loss below 45% relative humidity. These findings not only help understanding the adaptive success of mistletoe but may also be relevant for the development of new facile processing methods for next-generation cellulosic composites.
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IJS, KILJ, NUK, PNG, UL, UM
Berries from the European Mistletoe (Viscum album) possess a sticky tissue called viscin that facilitates adhesion and germination onto host trees. Recent studies of viscin have demonstrated its ...adhesive capacity on a range of natural and synthetic surfaces including wood, skin, metals, and plastic. Yet, the underlying mechanisms remain poorly understood. Here, an investigation of the adhesive performance of mistletoe viscin is performed, demonstrating its hygroscopic nature and ability to self‐heal following adhesive failure. It is identified that adhesion originates from a water‐soluble adhesive component that can be extracted, isolated, and characterized independently. Lap shear mechanical testing indicates that the mistletoe adhesive extract (MAE) outperforms native viscin tissue, as well as gum arabic and arabinogalactan—common plant‐based adhesives. Furthermore, humidity uptake experiments reveal that MAE can reversibly absorb nearly 100% of its mass in water from the atmosphere. In‐depth spectroscopic and mass spectrometry investigations reveal a composition consisting primarily of an atypical arabinogalactan, with additional sugar alcohols. Finally, several proof‐of‐concept applications are demonstrated using MAE for hygro‐responsive reversible adhesion between various surfaces including skin, plastic, PDMS, and paper, revealing that MAE holds potential as a biorenewable and reusable adhesive for applications in cosmetics, packaging, and potentially, tissue engineering.
Mistletoe viscin strongly and reversibly adheres to various surfaces, potentially providing a sustainably sourced adhesive for advanced applications. Yet, little is understood about the chemical basis of viscin's adhesive prowess. Here, a water‐soluble extract with impressive adhesive properties is isolated from viscin and characterized chemically. Importantly, this biosourced extract shows excellent promise in several industrially and biomedically relevant adhesive applications.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Abstract
Berries from the European Mistletoe (
Viscum album
) possess a sticky tissue called viscin that facilitates adhesion and germination onto host trees. Recent studies of viscin have ...demonstrated its adhesive capacity on a range of natural and synthetic surfaces including wood, skin, metals, and plastic. Yet, the underlying mechanisms remain poorly understood. Here, an investigation of the adhesive performance of mistletoe viscin is performed, demonstrating its hygroscopic nature and ability to self‐heal following adhesive failure. It is identified that adhesion originates from a water‐soluble adhesive component that can be extracted, isolated, and characterized independently. Lap shear mechanical testing indicates that the mistletoe adhesive extract (MAE) outperforms native viscin tissue, as well as gum arabic and arabinogalactan—common plant‐based adhesives. Furthermore, humidity uptake experiments reveal that MAE can reversibly absorb nearly 100% of its mass in water from the atmosphere. In‐depth spectroscopic and mass spectrometry investigations reveal a composition consisting primarily of an atypical arabinogalactan, with additional sugar alcohols. Finally, several proof‐of‐concept applications are demonstrated using MAE for hygro‐responsive reversible adhesion between various surfaces including skin, plastic, PDMS, and paper, revealing that MAE holds potential as a biorenewable and reusable adhesive for applications in cosmetics, packaging, and potentially, tissue engineering.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Natural materials provide an increasingly important role model for the development and processing of next-generation polymers. The velvet worm Euperipatoides rowelli hunts using a projectile, ...mechanoresponsive adhesive slime that rapidly and reversibly transitions into stiff glassy polymer fibers following shearing and drying. However, the molecular mechanism underlying this mechanoresponsive behavior is still unclear. Previous work showed the slime to be an emulsion of nanoscale charge-stabilized condensed droplets comprised primarily of large phosphorylated proteins, which under mechanical shear coalesce and self-organize into nano- and microfibrils that can be drawn into macroscopic fibers. Here, we utilize wide-angle X-ray diffraction and vibrational spectroscopy coupled with in situ shear deformation to explore the contribution of protein conformation and mechanical forces to the fiber formation process. Although previously believed to be unstructured, our findings indicate that the main phosphorylated protein component possesses a significant β-crystalline structure in the storage phase and that shear-induced partial unfolding of the protein is a key first step in the rapid self-organization of nanodroplets into fibers. The insights gained here have relevance for sustainable production of advanced polymeric materials.
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IJS, KILJ, NUK, PNG, UL, UM
Small specimens of spruce wood with different degrees of delignification were studied using in-situ tensile tests and simultaneous synchrotron X-ray diffraction to reveal the effect of ...delignification and densification on their tensile properties at relative humidities of 70–80 %. In addition to mechanical properties, these analyses yield the ratio of strains in the cellulose crystals and in the bulk, which reflects the stress-transfer to crystalline cellulose. While the specific modulus of elasticity slightly increases from native wood by partial or complete delignification, the lattice strain ratio does not show a significant change. This could indicate a compensatory effect from the decomposition of the amorphous matrix by delignification and from a tighter packing of cellulose crystals that would increase the stress transfer. The reduced strain to failure and maximum lattice strain of delignified specimens suggests that the removal of lignin affects the stress-strain behavior with fracture at lower strain levels.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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