Journal of Bionic Engineering (2024) 21:707–717 https://doi.org/10.1007/s42235-023-00460-9 

Detachment Behavior of Gecko Toe in Functional Strategies for Bionic Toe 

Qingfei Han1,2 · Wei Wang1  · Huan Shen1  · Xincheng Feng1  · Haoran Zhang1  · Qian Li1  · Yi Sun1  · Huapeng Wu2  · Aihong Ji1,3

1 Lab of Locomotion Bioinspiration and Intelligent Robots, College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China 2 Laboratory of Intelligent Machines, School of Energy Systems, Lappeenranta-Lahti University of Technology, 53850 Lappeenranta, Finland 3 State Key Laboratory of Mechanics and Control for Aerospace Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China 

Abstract Geckos can efciently navigate complex terrains due to their multi-level adhesive system that is present on their toes. The setae are responsible for the gecko’s extraordinary adhesion and have garnered wide attention from the scientifc community. The majority of the reported works in the literature that have dealt with the peeling models mainly focus on the gecko hierarchical adhesive system, with limited attention given to investigating the infuence of gecko toe structure on the detachment. Along these lines, to gain a deeper understanding of the rapid and efortless detachment abilities of gecko toes, the peeling behavior of gecko toes on vertical surfaces was primarily investigated in this work. More specifcally, the detachment time of a single toe on a smooth acrylic plate was measured to be 0.41±0.21 s. Moreover, it was observed that the toe assumed a "U"- shaped structure upon complete detachment. Additionally, Finite Element Analysis (FEA) models for three diferent types of gecko toes were developed to simulate both the displacement-peel and the moment-peel modes. Increasing the segmentation of the adhesive layer led to a gradual decrease in the resultant force, as well as the normal and tangential components. Lastly, a gecko-inspired toe model was constructed and powered by Shape Memory Alloy (SMA). A systematic comparison between the vertical drag separation and the outward fip separation was also conducted. From our analysis, it was clearly demonstrated that outward peel separation signifcantly necessitated the reduction of the peeling force, thus confrming the advantageous nature of the outward motion in gecko toe detachment. Our data not only contribute to a deeper understanding of the gecko detachment behavior but also ofer valuable insights for the advancement of the wall-climbing robot feet. 

Keywords Gecko toes · Detachment behavior · Finite element analysis · Gecko-inspired toe