Digital hyperextension has no influence on the active self‐drying of gecko adhesive subdigital pads

• Published in: Journal of experimental zoology. Part A, Ecological and integrative physiology Vol. 333; no. 2; pp. 118 - 125
• Main Authors: Garner, Austin M., Buo, Carrie, Piechowski, Jennifer M., Pamfilie, Alexandra M., Stefanovic, Sharon R., Dhinojwala, Ali, Niewiarowski, Peter H.
• Format: Journal Article
• Language: English
• Published: United States 01-02-2020
• Subjects: adhesion; Adhesiveness; Animals; Biomechanical Phenomena; Extremities - physiology; Gekko gecko; Gekkonidae; Lizards - physiology; van der Waals; Walking; Water; Wettability; wetting; van der Waals; Gekko gecko; Gekkonidae; wetting; adhesion
• ISSN: 2471-5638; 2471-5646
• DOI: 10.1002/jez.2332

The remarkable properties of the gecko adhesive system have been intensively studied. Although many gecko‐inspired synthetic adhesives have been designed and fabricated, few manage to capture the multifunctionality of the natural system. Analogous to previously documented self‐cleaning, recent work demonstrated that gecko toe pads dry when geckos take steps on dry substrates (i.e., self‐drying). Whether digital hyperextension (DH), the distal to proximal peeling of gecko toe pads, is involved in the self‐drying process, had not been determined. Here, the effect of DH on self‐drying was isolated by preventing DH from occurring during normal walking locomotion of Gekko gecko after toe pads were wetted. Our initial analysis revealed low statistical power, so we increased our sample size to determine the robustness of our result. We found that neither DH nor the DH–substrate interaction had a significant effect on the maximum shear adhesive force after self‐drying. These results suggest that DH is not necessary for self‐drying to occur. Interestingly, however, we discovered that shear adhesion is higher on a surface tending hydrophobic compared to a hydrophilic surface, demonstrating that gecko adhesion is sensitive to substrate wettability during the subdigital pad drying process. Furthermore, we also observed frequent damage to the adhesive system during shear adhesion testing post‐drying, indicating that water may compromise the structural integrity of the adhesive structures. Our results not only have behavioral and ecological implications for free‐ranging geckos but also have the potential to influence the design and fabrication of gecko‐inspired synthetic adhesives that can regain adhesion after fouling with water.
Digital hyperextension (DH), the distoproximal peeling of gecko adhesive subdigital pads, was experimentally prevented in Gekko gecko to examine whether DH influences the extent of gecko self‐drying. Overall, we found that DH has no impact on maximum shear force after self‐drying, suggesting that its effect on active self‐drying is minimal or nonexistent. Interestingly, we also discovered that gecko adhesion is sensitive to substrate wettability during the self‐drying process and prolonged exposure to water may diminish the structural integrity of gecko adhesive setae.
RESEARCH HIGHLIGHTS
Gecko adhesive pads self‐dry to the same extent with or without digital hyperextension. Shear adhesion after self‐drying is sensitive to substrate wettability and prolonged water exposure may diminish the structural integrity of gecko adhesive setae.