Elastic modulus of tree frog adhesive toe pads

Previous work using an atomic force microscope in nanoindenter mode indicated that the outer, 10- to 15-μm thick, keratinised layer of tree frog toe pads has a modulus of elasticity equivalent to silicone rubber (5–15 MPa) (Scholz et al. 2009), but gave no information on the physical properties of d...

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Bibliographic Details
Published in:Journal of Comparative Physiology 2011-10, Vol.197 (10), p.969-978, Article 969
Main Authors: Barnes, W. Jon. P, Goodwyn, Pablo J. Perez, Nokhbatolfoghahai, Mohsen, Gorb, Stanislav N
Format: Article
Language:English
Subjects:
adhesion
Adhesiveness
adults
Age Factors
Animal Physiology
Animals
Anura - physiology
Biomechanical Phenomena
Biomedical and Life Sciences
Elastic Modulus
Epidermis - physiology
Forelimb
frogs
Hindlimb
Interferometry
keratinization
Life Sciences
Litoria
modulus of elasticity
Neurosciences
Original Paper
Pressure
rubber
silicone
Toes - physiology
Transducers, Pressure
Zoology
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Summary:Previous work using an atomic force microscope in nanoindenter mode indicated that the outer, 10- to 15-μm thick, keratinised layer of tree frog toe pads has a modulus of elasticity equivalent to silicone rubber (5–15 MPa) (Scholz et al. 2009), but gave no information on the physical properties of deeper structures. In this study, micro-indentation is used to measure the stiffness of whole toe pads of the tree frog, Litoria caerulea. We show here that tree frog toe pads are amongst the softest of biological structures (effective elastic modulus 4–25 kPa), and that they exhibit a gradient of stiffness, being stiffest on the outside. This stiffness gradient results from the presence of a dense network of capillaries lying beneath the pad epidermis, which probably has a shock absorbing function. Additionally, we compare the physical properties (elastic modulus, work of adhesion, pull-off force) of the toe pads of immature and adult frogs.
ISSN:0340-7594
1432-1351
DOI:10.1007/s00359-011-0658-1