The biomechanics of tree frogs climbing curved surfaces: a gripping problem

Hill, I. D.C., Dong, B., Barnes, W. J. P., Ji, A. and Endlein, T. (2018) The biomechanics of tree frogs climbing curved surfaces: a gripping problem. Journal of Experimental Biology, 221(5), jeb168179. (doi: 10.1242/jeb.168179) (PMID:29361584)

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The adhesive mechanisms of climbing animals have become an important research topic because of their biomimetic implications. We examined the climbing abilities of hylid tree frogs on vertical cylinders of differing diameter and surface roughness to investigate the relative roles of adduction forces (gripping) and adhesion. Tree frogs adhere using their toe pads and subarticular tubercles, the adhesive joint being fluid-filled. Our hypothesis was that, on an effectively flat surface (adduction forces on the largest 120 mm diameter cylinder were insufficient to allow climbing), adhesion would effectively be the only means by which tree frogs could climb, but on the two smaller diameter cylinders (44 mm and 13 mm), frogs could additionally utilise adduction forces by gripping the cylinder either with their limbs outstretched or by grasping around the cylinder with their digits, respectively. The frogs' performance would also depend on whether the surfaces were smooth (easy to adhere to) or rough (relatively non-adhesive). Our findings showed that climbing performance was highest on the narrowest smooth cylinder. Frogs climbed faster, frequently using a 'walking trot' gait rather than the 'lateral sequence walk' used on other cylinders. Using an optical technique to visualize substrate contact during climbing on smooth surfaces, we also observed an increasing engagement of the subarticular tubercles on the narrower cylinders. Finally, on the rough substrate, frogs were unable to climb the largest diameter cylinder, but were able to climb the narrowest one slowly. These results support our hypotheses and have relevance for the design of climbing robots.

Item Type:Articles
Keywords:Adhesion, climbing, Tree frog.
Glasgow Author(s) Enlighten ID:Hill, Mr Iain and Barnes, Dr William
Authors: Hill, I. D.C., Dong, B., Barnes, W. J. P., Ji, A., and Endlein, T.
College/School:College of Medical Veterinary and Life Sciences > School of Molecular Biosciences
College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
Journal Name:Journal of Experimental Biology
Publisher:Company of Biologists
ISSN (Online):1477-9145
Published Online:19 January 2018
Copyright Holders:Copyright © 2018 The Company of Biologists Ltd.
First Published:First published in Journal of Experimental Biology 221(5): jeb168179
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
677801Use of clamping grips & friction pads for climbing curved surfaces in tree frogsWilliam BarnesThe Royal Society (ROYSOC)IE140717RI MOLECULAR CELL & SYSTEMS BIOLOGY