Understanding tree frog adhesion

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Our ongoing effort is aimed at understanding the role of the tree frogs structured toe pads in promoting adhesion under flooded conditions. The locomotion mechanisms employed by tree frogs under flooded conditions could offer the ultimate solution for the need of strong, reversible, reusable, tunable, and water tolerant adhesives. Central to the adhesion and locomotion of tree frogs are their structured toe pads, which consist of an array interconnected channels that end in mucus secreting glands. On dry surfaces, the toe pads enhance adhesion via deformation of the soft epithelial cells to improve foot-surface conformity and secretion of watery-mucus into the area of contact to promote capillary or hydrodynamic interactions. Under flooded conditions, however, capillary interactions are expected to be negligible given the absence of any free fluid interface. The mechanisms for tree frog adhesion under flooded conditions, and by extension the role played by the structured toe pads, has been the subject of speculations. It is suspected that tree frogs can climb and grip on wet surfaces (and prevent hydroplaning) by reducing the hydrodynamic forces through drainage of the fluid in the channels present on their toe pads. While hypothesized, the mechanism for tree frog adhesion, and more specifically the role played by hydrodynamics and elastic deformation, has not been clearly demonstrated. Moreover, the potential of biomimetic materials based on the tree frog toe pads has yet to be realized. 

Papers:

Measurement and scaling of hydrodynamic interactions in the presence of draining channels (Langmuir)

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