Effects of humidity on the mechanical properties of gecko setae

We tested the hypothesis that an increase in relative humidity (RH) causes changes in the mechanical properties of the keratin of adhesive gecko foot hairs (setae). We measured the effect of RH on the tensile deformation properties, fracture, and dynamic mechanical response of single isolated tokay...

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Bibliographic Details
Published in:Acta biomaterialia 2011-02, Vol.7 (2), p.733-738
Main Authors: Prowse, Michael S., Wilkinson, Matt, Puthoff, Jonathan B., Mayer, George, Autumn, Kellar
Format: Article
Language:English
Subjects:
absorption
Adhesion
Animals
Biomechanical Phenomena - physiology
deformation
Elastic Modulus
Epidermis - ultrastructure
Failure
friction
Gecko
Geckos
hairs
Humidity
Humidity effects
keratin
Keratins
Lizards - physiology
Mechanical properties
modulus of elasticity
Relative humidity
Sensilla - physiology
Sensilla - ultrastructure
Seta
Stress, Mechanical
Tensile deformation
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Summary:We tested the hypothesis that an increase in relative humidity (RH) causes changes in the mechanical properties of the keratin of adhesive gecko foot hairs (setae). We measured the effect of RH on the tensile deformation properties, fracture, and dynamic mechanical response of single isolated tokay gecko setae and strips of the smooth lamellar epidermal layer. The mechanical properties of gecko setae were strongly affected by RH. The complex elastic modulus (measured at 5 Hz) of a single seta at 80% RH was 1.2 GPa, only 39% of the value when dry. An increase in RH reduced the stiffness and increased the strain to failure. The loss tangent increased significantly with humidity, suggesting that water absorption produces a transition to a more viscous type of deformation. The influence of RH on the properties of the smooth epidermal layer was comparable with that of isolated seta, with the exception of stress at rupture. These values were two to four times greater for the setae than for the smooth layer. The changes in mechanical properties of setal keratin were consistent with previously reported increases in contact forces, supporting the hypothesis that an increase in RH softens setal keratin, which increases adhesion and friction.
ISSN:1742-7061
1878-7568
DOI:10.1016/j.actbio.2010.09.036