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Helical Crossed-Fiber Structure in Flight Feathers
From: Ben Creisler
New in PLoS ONE:
Lingham-Soliar T, Murugan N (2013)
Theagarten Lingham-Soliar & Nelisha Murugan (2013)
A New Helical Crossed-Fibre Structure of β-Keratin in Flight Feathers
and Its Biomechanical Implications.
PLoS ONE 8(6): e65849.
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.