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Ultrastructure and physical properties of an adhesive surface, the toe pad epithelium of the tree frog, Litoria caerulea White

Authors :
Joanna Smith
Ingo Scholz
W. J. P. Barnes
Werner Baumgartner
Source :
Journal of Experimental Biology. 212:155-162
Publication Year :
2009
Publisher :
The Company of Biologists, 2009.

Abstract

SUMMARY Knowledge of both surface structure and physical properties such as stiffness and elasticity are essential to understanding any adhesive system. In this study of an adhesion surface in the tree frog, Litoria caerulea White, a variety of techniques including atomic force microscopy were used to investigate the microstructure and properties of an epithelium that adheres through wet adhesion. Litoria toe pads consist of a hexagonal array of flat-topped epithelial cells, separated by mucus-filled channels. Under an atomic force microscope, this `flat' surface is highly structured at the nanoscale, consisting of a tightly packed array of columnar nanopillars (described as hemidesmosomes by previous authors), 326±84 nm in diameter, each of which possesses a central dimple 8±4 nm in depth. In fixed tissue (transmission electron microscopy), the nanopillars are approximately as tall as they are broad. At the gross anatomical level, larger toe pads may be subdivided into medial and lateral parts by two large grooves. Although the whole toe pad is soft and easily deformable, the epithelium itself has an effective elastic modulus equivalent to silicon rubber (mean Eeff=14.4±20.9 MPa; median Eeff=5.7 MPa), as measured by the atomic force microscope in nanoindentation mode. The functions of these structures are discussed in terms of maximising adhesive and frictional forces by conforming closely to surface irregularities at different length scales and maintaining an extremely thin fluid layer between pad and substrate. The biomimetic implications of these findings are reviewed.

Details

ISSN :
14779145 and 00220949
Volume :
212
Database :
OpenAIRE
Journal :
Journal of Experimental Biology
Accession number :
edsair.doi.dedup.....61d88445de9f232a55a4cd8f93eabe3f
Full Text :
https://doi.org/10.1242/jeb.019232