Molecular Orientation of Some Keratins

Earland, Christopher; Blakey, P. R.; Stell, J. G. P.

doi:10.1038/1961287a0

Cited by 33 publications

(15 citation statements)

References 3 publications

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“…This cortical description in the rachis is modified here to include at the surface one or two layers of syncitial barbule cells aligned with the long axis of the rachis, possibly for better aerodynamics (similarly in the barbs). Two things are, however, comparable in Earland et als’ [12] and Lingham-Soliar et als’ [4] findings, the depth of the outer layer of approximataly 15% the total cortical depth and the inclination of the fibres at approximately 70° to the rachidial long axis. Interestingly, in the context of selective biodegradation here, Earland et al [12] intuitively raised doubts based on their X-ray diffraction patterns of chemical fractions as to whether or not native feather keratin is in an exclusively β-configuration and suggested the possibility that it contains some α-protein [6], [7].…”

Section: Discussionmentioning

confidence: 56%

“…It is important not to confuse it with findings by X-ray diffraction analyses that suggest an anisotropic fibre structure of the feather rachis [12]. Based on their x-ray diffraction study, Earland et al (12) proposed that the feather calamus was “polyphase in structure, consisting of an interior layer with molecular orientation along the axis, and an exterior layer with orientation at right angles to the axis” i.e.…”

Section: Discussionmentioning

confidence: 99%

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A New Helical Crossed-Fibre Structure of β-Keratin in Flight Feathers and Its Biomechanical Implications

Lingham‐Soliar

Murugan

2013

PLoS ONE

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The feather aerofoil is unequalled in nature. It is comprised of a central rachis, serial paired branches or barbs, from which arise further branches, the barbules. Barbs and barbules arise from the significantly thinner lateral walls (the epicortex) of the rachis and barbs respectively, as opposed to the thicker dorsal and ventral walls (the cortex). We hypothesized a microstructural design of the epicortex that would resist the vertical or shearing stresses. The microstructures of the cortex and epicortex of the rachis and barbs were investigated in several bird species by microbe-assisted selective disassembly and conventional methods via scanning electron microscopy. We report, preeminent of the finds, a novel system of crossed fibres (ranging from ∼100–800 nm in diameter), oppositely oriented in alternate layers of the epicortex in the rachis and barbs. It represents the first cross-fibre microstructure, not only for the feather but in keratin per se. The cortex of the barbs is comprised of syncitial barbule cells, definitive structural units shown in the rachidial cortex in a related study. The structural connection between the cortex of the rachis and barbs appears uninterrupted. A new model on feather microstructure incorporating the findings here and in the related study is presented. The helical fibre system found in the integument of a diverse range of invertebrates and vertebrates has been implicated in profound functional strategies, perhaps none more so potentially than in the aerofoil microstructure of the feather here, which is central to one of the marvels of nature, bird flight.

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Section: Discussionmentioning

confidence: 56%

Section: Discussionmentioning

confidence: 99%

A New Helical Crossed-Fibre Structure of β-Keratin in Flight Feathers and Its Biomechanical Implications

Lingham‐Soliar

Murugan

2013

PLoS ONE

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“…Earlier studies [244] also showed similar longitudinal variations in Young's modulus along feather length in four different species of birds. This may be due to the structural changes of the cortex: as moving from the proximal to the distal part, the thickness of the inner layer with keratin fibers aligned parallel to the axis of the feather becomes larger [246,247], indicating that the fraction of longitudinally aligned filaments increases from the proximal end to the distal end; therefore the stiffness of the cortex increases. Cameron et al [248] reported that a higher axial alignment of keratin fibers and a higher Young's modulus along the rachis length toward the feather's tip in flying bird species (geese and swans), whereas such trend was absent in the non-flying ostrich.…”

Section: Feathersmentioning

confidence: 99%

Keratin: Structure, mechanical properties, occurrence in biological organisms, and efforts at bioinspiration

Wang

Yang

McKittrick

et al. 2016

Progress in Materials Science

682

474

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a b s t r a c tA ubiquitous biological material, keratin represents a group of insoluble, usually high-sulfur content and filament-forming proteins, constituting the bulk of epidermal appendages such as hair, nails, claws, turtle scutes, horns, whale baleen, beaks, and feathers. These keratinous materials are formed by cells filled with keratin and are considered 'dead tissues'. Nevertheless, they are among the toughest biological materials, serving as a wide variety of interesting functions, e.g. scales to armor body, horns to combat aggressors, hagfish slime as defense against predators, nails and claws to increase prehension, hair and fur to protect against the environment. The vivid inspiring examples can offer useful solutions to design new structural and functional materials.Keratins can be classified as a-and b-types. Both show a characteristic filament-matrix structure: 7 nm diameter intermediate filaments for a-keratin, and 3 nm diameter filaments for b-keratin.Both are embedded in an amorphous keratin matrix. The molecular unit of intermediate filaments is a coiled-coil heterodimer and that of b-keratin filament is a pleated sheet. The mechanical response of a-keratin has been extensively studied and shows linear Hookean, yield and post-yield regions, and in some cases, a high reversible elastic deformation. Thus, they can be also be considered 'biopolymers'. On the other hand, b-keratin has not been investigated as comprehensively. Keratinous materials are strain-rate sensitive, and the effect of hydration is significant.Keratinous materials exhibit a complex hierarchical structure: polypeptide chains and filament-matrix structures at the nanoscale, Progress in Materials Science 76 (2016) 229-318 Contents lists available at ScienceDirect Progress in Materials Sciencej o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / p m a t s c i organization of keratinized cells into lamellar, tubular-intertubular, fiber or layered structures at the microscale, and solid, compact sheaths over porous core, sandwich or threads at the macroscale. These produce a wide range of mechanical properties: the Young's modulus ranges from 10 MPa in stratum corneum to about 2.5 GPa in feathers, and the tensile strength varies from 2 MPa in stratum corneum to 530 MPa in dry hagfish slime threads. Therefore, they are able to serve various functions including diffusion barrier, buffering external attack, energy-absorption, impact-resistance, piercing opponents, withstanding repeated stress and aerodynamic forces, and resisting buckling and penetration.A fascinating part of the new frontier of materials study is the development of bioinspired materials and designs. A comprehensive understanding of the biochemistry, structure and mechanical properties of keratins and keratinous materials is of great importance for keratin-based bioinspired materials and designs. Current bioinspired efforts including the manufacturing of quill-inspired aluminum composites, animal horn-inspired SiC composites, and feather-i...

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“…Man-made composite beams reinforced with longitudinally oriented fibres should also be prone to greenstick fracture, because of failure by the Cook-Gordon mechanism. The need to prevent such longitudinal splitting may be the reason why the shafts of feathers, which are composed almost entirely of longitudinally reinforced keratin, also have a thin outer layer of tangentially oriented keratin fibres (Earland et al 1962). …”

Section: (D) Straight Branchesmentioning

confidence: 99%

Transverse stresses and modes of failure in tree branches and other beams

Ennos

Casteren

2009

Proc. R. Soc. B.

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The longitudinal stresses in beams subjected to bending also set up transverse stresses within them; they compress the cross section when the beam's curvature is being increased and stretch it when its curvature is being reduced. Analysis shows that transverse stresses rise to a maximum at the neutral axis and increase with both the bending moment applied and the curvature of the beam. These stresses can qualitatively explain the fracture behaviour of tree branches. Curved 'hazard beams' that are being straightened split down the middle because of the low transverse tensile strength of wood. By contrast, straight branches of light wood buckle when they are bent because of its low transverse compressive strength. Branches of denser wood break, but the low transverse tensile strength diverts the crack longitudinally when the fracture has only run half-way across the beam, to produce their characteristic 'greenstick fracture'. The bones of young mammals and uniaxially reinforced composite beams may also be prone to greenstick fracture because of their lower transverse tensile strength.

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Molecular Orientation of Some Keratins

Cited by 33 publications

References 3 publications

A New Helical Crossed-Fibre Structure of β-Keratin in Flight Feathers and Its Biomechanical Implications

A New Helical Crossed-Fibre Structure of β-Keratin in Flight Feathers and Its Biomechanical Implications

Keratin: Structure, mechanical properties, occurrence in biological organisms, and efforts at bioinspiration

Transverse stresses and modes of failure in tree branches and other beams

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