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Type: Article × Subject: Tensile strength ×

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    Amyloids: From molecular structure to mechanical properties
    (Amsterdam [u.a.] : Elsevier, 2013) Schleeger, M.; Vandenakker, C.C.; Deckert-Gaudig, T.; Deckert, V.; Velikov, K.P.; Koenderink, G.; Bonn, M.
    Many proteins of diverse sequence, structure and function self-assemble into morphologically similar fibrillar aggregates known as amyloids. Amyloids are remarkable polymers in several respects. First of all, amyloids can be formed from proteins with very different amino acid sequences; the common denominator is that the individual proteins constituting the amyloid fold predominantly into a β-sheet structure. Secondly, the formation of the fibril occurs through non-covalent interactions between primarily the β-sheets, causing the monomers to stack into fibrils. The fibrils are remarkably robust, considering that the monomers are bound non-covalently. Finally, a common characteristic of fibrils is their unbranched, straight, fiber-like structure arising from the intertwining of the multiple β-sheet filaments. These remarkably ordered and stable nanofibrils can be useful as building blocks for protein-based functional materials, but they are also implicated in severe neurodegenerative diseases. The overall aim of this article is to highlight recent efforts aimed at obtaining insights into amyloid proteins on different length scales. Starting from molecular information on amyloids, single fibril properties and mechanical properties of networks of fibrils are described. Specifically, we focus on the self-assembly of amyloid protein fibrils composed of peptides and denatured model proteins, as well as the influence of inhibitors of fibril formation. Additionally, we will demonstrate how the application of recently developed vibrational spectroscopic techniques has emerged as a powerful approach to gain spatially resolved information on the structure-function relation of amyloids. While spectroscopy provides information on local molecular conformations and protein secondary structure, information on the single fibril level has been developed by diverse microscopic techniques. The approaches to reveal basic mechanical properties of single fibrils like bending rigidity, shear modulus, ultimate tensile strength and fracture behavior are illustrated. Lastly, mechanics of networks of amyloid fibrils, typically forming viscoelastic gels are outlined, with a focus on (micro-) rheological properties. The resulting fundamental insights are essential for the rational design of novel edible and biodegradable protein-based polymers, but also to devise therapeutic strategies to combat amyloid assembly and accumulation during pathogenic disorders.
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    Scaling of bird wings and feathers for efficient flight
    (Washington, D.C. : American Association for the Advancement of Science, 2019) Sullivan, T.N.; Meyers, M.A.; Arzt, E.
    Aves are an incredibly diverse class of animals, ranging greatly in size and thriving in a wide variety of environments. Here, we explore the scaling trends of bird wings in connection with their flight performance. The tensile strength of avian bone is hypothesized to be a limiting factor in scaling the humerus with mass, which is corroborated by its experimentally determined allometric scaling trend. We provide a mechanics analysis that explains the scaling allometry of the wing humerus length, L H , with body weight W, L H ∝ W 0.44 . Lastly, wing feathers are demonstrated to generally scale isometrically with bird mass, with the exception of the spacing between barbules, which falls within the same range for birds of all masses. Our findings provide insight into the “design” of birds and may be translatable to more efficient bird-inspired aircraft structures. © 2019 American Association for the Advancement of Science. All rights reserved.
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    Renewable vanillin based flame retardant for poly(lactic acid): A way to enhance flame retardancy and toughness simultaneously
    (London : RSC Publishing, 2018) Zhao, Pengcheng; Liu, Zhiqi; Wang, Xueyi; Pan, Ye-Tang; Kuehnert, Ines; Gehde, Michael; Wang, De-Yi; Leuteritz, Andreas
    In this study, a novel bio-based flame retardant material consisting of modified vanillin and poly(lactic acid) (PLA) was developed by incorporation of newly discovered additive, bis(5-formyl-2-methoxyphenyl) phenylphosphonate (VP), into the PLA matrix. The chemical structure of VP was confirmed by 1 H-, 13 C- and 31 P NMR and FTIR. The flame retardancy, thermal behavior as well as the mechanical properties of PLA/VP composites were evaluated. With 5 wt% of VP, the LOI of PLA increased from 21.4 to 25.8 and passed the UL-94 V-0 classification. Additionally, the elongation at break was improved from 3% to 11% without sacrificing tensile strength. In an effort to understand the mechanisms, TGA-FTIR, TGA and SEM were performed. This paper suggests a new possibility to prepare polymeric composites with enhanced flame retardancy from sustainable resources.