Incline-dependent adjustments of toes in geckos inspire functional strategies for biomimetic manipulators

Geckos show versatility by rapidly maneuvering on diverse complex terrain because they benefit from the distributed, setae-covered toes and thus the ability to generate reliable and adaptive attachment. Significant attention has been paid to their adhesive microstructures (setae), but the effectivness of the gecko’s adaptive attachment at the level of toes and feet remains unclear. Aiming to better understand geckos’ attachment, we first focused on the deployment of toes by challenging geckos to locomote on varying inclines. When the slope angle was less than than 30°, feet mainly interacted with the substrate using the bases of toes and generated anisotropic frictional forces. As the slope angle increased to 90°, the participation of toe bases was reduced. Instead, the setae contribution increased for the middle three toes of the front feet and for the first three toes of the hind feet. As the incline changed from vertical to inverted, the adhesive contribution of the toes at the front feet became more equal, whereas the effective adhesion contact of the hind feet gradually shifted to the toes oriented rearward. Second, a mathematical model was established and then suggested the potential advantages of distributed control among toes to regulate foot force. Finally, a physical foot model containing five compliant, adjustable toes was constructed and validated the animal discoveries. By using the gecko toes’ control strategies, the artificial foot demonstrated diverse behavior regulating attachment forces. The success of the foot prototype not only tested our understanding of the mechanism of biological attachment, but also provided a demonstration for the design and control of gecko-inspired attachment devices, grippers, and other manipulators.