Optimal Angles for Maximal Adhesion in Living Tokay Geckos

Non-linear double-peeling: Experimental vs. theoretical predictions

“…6), as shown in [47], where it is demonstrated that the total energy takes a maximum value (and, hence, unstable) for peeling angles θ eq < θ lim . In our experiments, the tape is not very compliant and, as a result, it has a high elastic modulus, so θ was much lower than the one found for living animals [23], which have also a very high effective adhesion energy because they use a hierarchical peeling system and a smart body adaptation to optimize adhesion and detachment. Therefore, they can better adhere to surfaces yet detach quickly using low forces.…”

“…The angle giving optimal adhesion could be used in nature by animals to maximize adhesion at all the different hierarchical levels, such as contralateral legs, toes and even setae for geckos [23]. In addition, the optimal angle could also be used in nature to optimize the strength of natural anchors [8,26].…”

“…Several scientific studies have been developed to establish the value of such an adhesion angle α from an experimental [9][10]21], theoretical or computational [12][13]18, 32] point of view and at different characteristic sizes of the hierarchical adhesive system. From previously published scientific papers, the adhesion angle θ of Tokay geckos is equal to ~29° [23] for opposing front and rear feet, ~27.3 [23] between the first and fifth toe of each foot, ~25.5° [20] for a single toe, ~24.6° [20] (or ~30° [22]) for isolated setae arrays and ~30.0° [20] (or ~31° [22]) for a single seta.…”

“…For example, in order to maintain the necessary shear/frictional adhesive forces and to avoid toe detachment, the Tokay gecko's (Gekko gecko) adhesive mechanism is based on the use of opposing feet and toes making a V-shaped geometry. The gecko then pulls its feet inwards towards the center of its body mass and its toes inwards towards the foot to engage adhesion [23,10].…”

“…Starting with research [8][9][10][11][12][13][14][15][16][17][18][19] on the adhesion behavior of lizards (like gecko, for instance) and arthropods (like beetles or spiders), a great deal of experimental [20][21][22][23][24] and theoretical [25][26][27][28][29][30][31] work has been done to study the mechanism of adhesion and detachment of natural systems.…”