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The use of clamping grips and friction pads by tree frogs for climbing curved surfaces

2017

Conference Paper

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Most studies on the adhesive mechanisms of climbing animals have addressed attachment against flat surfaces, yet many animals can climb highly curved surfaces, like twigs and small branches. Here we investigated whether tree frogs use a clamping grip by recording the ground reaction forces on a cylindrical object with either a smooth or anti-adhesive, rough surface. Furthermore, we measured the contact area of fore and hindlimbs against differently sized transparent cylinders and the forces of individual pads and subarticular tubercles in restrained animals. Our study revealed that frogs use friction and normal forces of roughly a similar magnitude for holding on to cylindrical objects. When challenged with climbing a non-adhesive surface, the compressive forces between opposite legs nearly doubled, indicating a stronger clamping grip. In contrast to climbing flat surfaces, frogs increased the contact area on all limbs by engaging not just adhesive pads but also subarticular tubercles on curved surfaces. Our force measurements showed that tubercles can withstand larger shear stresses than pads. SEM images of tubercles revealed a similar structure to that of toe pads including the presence of nanopillars, though channels surrounding epithelial cells were less pronounced. The tubercles' smaller size, proximal location on the toes and shallow cells make them probably less prone to buckling and thus ideal for gripping curved surfaces.

Author(s): Endlein, Thomas and Ji, Aihong and Yuan, Shanshan and Hill, Iain and Wang, Huan and Barnes, W Jon P and Dai, Zhendong and Sitti, Metin
Book Title: Proc. R. Soc. B
Volume: 284
Number (issue): 1849
Pages: 20162867
Year: 2017
Month: Febuary
Day: 22

Department(s): Physical Intelligence
Bibtex Type: Conference Paper (inproceedings)

DOI: 10.1098/rspb.2016.2867

Organization: The Royal Society

BibTex

@inproceedings{endlein2017use,
  title = {The use of clamping grips and friction pads by tree frogs for climbing curved surfaces},
  author = {Endlein, Thomas and Ji, Aihong and Yuan, Shanshan and Hill, Iain and Wang, Huan and Barnes, W Jon P and Dai, Zhendong and Sitti, Metin},
  booktitle = {Proc. R. Soc. B},
  volume = {284},
  number = {1849},
  pages = {20162867},
  organization = {The Royal Society},
  month = feb,
  year = {2017},
  month_numeric = {2}
}