Size, shape and orientation of macro-sized substrate protrusions affect the toe and foot adhesion of geckos

Rate-dependent adhesion together with limb collaborations facilitate grasshoppers reliable attachment under highly dynamic conditions

Dynamic attachment is indispensable for animals to cope with unexpected disturbances. Minor attention has been paid to the dynamic performance of insects' adhesive pads. Through experiments pulling whole grasshoppers off a glass rod at varying speeds, surprising findings emerged. The feet did not always maintain contact but released and then reconnected to the substrate rapidly during leg extension, potentially reducing the shock damage to pads. As the pulling speeds increased from 1 to 400 mm/s, the maximum forces of single front tarsus insects and entire tarsi insects were nearly proportional to the 1/3 power of pulling speeds by 0.11 and 0.29 times, respectively. The force of some individuals could be even 800 times greater than their weight, which is unexpectedly high for smooth insect pads. This work not only helps us to understand the attachment intelligence of animals but is also informative for artificial attachment in extreme situations.

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 their distributed, setae-covered toes and thus have the ability to generate reliable and adaptive attachment. Significant attention has been paid to their adhesive microstructures (setae), but the effectiveness of the gecko's adaptive attachment at the level of toes and feet remains unclear. In order to better understand the geckos' attachment, we first focused on the deployment of toes while challenging geckos to locomote on varying inclines. When the slope angle was less than 30°, their feet mainly interacted with the substrate using the bases of the toes and generated anisotropic frictional forces. As the slope angle increased to 90°, the participation of the 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 of the front feet became more equal, whereas the effective adhesion contact of the hind feet gradually shifted to the toes oriented rearwards. Second, a mathematical model was established and then suggested the potential advantages of distributed control among the toes to regulate foot force. Finally, a physical foot model containing five compliant, adjustable toes was constructed and validated the discoveries with regard to the animals. 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.

Peking geckos (Gekko swinhonis) traversing upward steps: the effect of step height on the transition from horizontal to vertical locomotion

The ability to transition between surfaces (e.g., from the ground to vertical barriers, such as walls, tree trunks, or rock surfaces) is important for the Peking gecko's (Gekko swinhonis Günther 1864) survival. However, quantitative research on gecko's kinematic performance and the effect of obstacle height during transitional locomotion remains scarce. In this study, the transitional locomotion of geckos facing different obstacle heights was assessed. Remarkably, geckos demonstrated a bimodal locomotion ability, as they could climb and jump. Climbing was more common on smaller obstacles and took longer than jumping. The jumping type depended on the obstacle height: when geckos could jump onto the obstacle, the vertical velocity increased with obstacle height; however, geckos jumped from a closer position when the obstacle height exceeded this range and would get attached to the vertical surface. A stability analysis of vertical surface landing using a collision model revealed that geckos can reduce their restraint impulse by increasing the landing angle through limb extension close to the body, consequently dissipating collision energy and reducing their horizontal and vertical velocities. The findings of this study reveal the adaptations evolved by geckos to move in their environments and may have applicability in the robotics field.