Abstract
Geckos’ ability to move on steep surfaces depends on their excellent adhesive structure, timely adjustments on locomotor behaviors, and elaborates control on reaction forces. However, it is still unclear how they can generate a sufficient driving force that is necessary for locomotion, while ensuring reliable adhesion on steep inclines. We measured the forces acting on each foot and recorded the contact states between feet and substrates when geckos encountered smooth inclination challenges ranging from 0° to 180°. The critical angles of the resultant force vectors of the front and hind-feet increased with respect to the incline angles. When the incline angle became greater than 120°, the critical angles of the front- and hind-feet were similar, and the averages of the critical angles of the front- and hind-feet were both smaller than 120°, indicating that the complicated and accurate synergy among toes endows gecko’s foot an obvious characteristic of “frictional adhesion” during locomotion. Additionally, we established a contact mechanical model for gecko’s foot in order to quantify the contribution of the frictional forces generated by the heel, and the adhesion forces generated by the toes on various inclines. The synergy between multiple contact mechanisms (friction or adhesion) is critical for the reliable attachment on an inclined surface, which is impossible to achieve by using a single-contact mechanism, thereby increasing the animal’s ability to adapt to its environment.
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Acknowledgements
We thank Chao Wu, We Li, and Qijun Jiang for assistance with data collection and manuscript writing. Yi Song and Lei Cai provided insightful comments on the manuscript. This work was supported by the National Natural Science Foundation of China (Grant No. 51435008 to Z.D. and 31601870 to Z.W.) and Natural Science Foundation of Jiangsu Province, China (Grant No. SBK2016040649 to Z.W.).
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Zhouyi WANG. He obtained his doctor degree in 2015 from College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics (NUAA). He currently works at the College of Astronautics at the NUAA. He was awarded the Shangyin Excellent Mechanical Doctoral Dissertation Award (Bronze) in 2016. His interested research areas include tribology, bionics, and animal kinematics and dynamics.
Zhendong DAI. Male, professor, and tutor of PhD Students, he obtained his doctor degree in 1999 from College of Mechanical and Electrical Engineering, NUAA. He is one of the Chinese delegates of International Institute of Bionic Engineering, an executive member of the Council of Chinese Mechanical Engineering in Tribology, and a member of the Academic Committee, State Key Laboratory of Solid Lubrication. He also is member of editorial board of many magazines such as Journal of Bionic Engineering, International Journal of Vehicle Autonomous System, Tribology, and so on. His research areas include bionics, light material, control of bionics, bio‐robots, and biological robots. He has successively presided and participated in many research projects and has published more than 200 papers and gotten more than 20 patents.
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Wang, Z., Xing, Q., Wang, W. et al. Contribution of friction and adhesion to the reliable attachment of a gecko to smooth inclines. Friction 6, 407–419 (2018). https://doi.org/10.1007/s40544-017-0174-6
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DOI: https://doi.org/10.1007/s40544-017-0174-6