Reversible Adhesive Bio-Toe with Hierarchical Structure Inspired by Gecko

• Published in: Biomimetics (Basel, Switzerland) Switzerland), 2023-01, Vol.8 (1), p.40
• Main Authors: Wang, Liuwei, Wang, Zhouyi, Wang, Bingcheng, Yuan, Qingsong, Weng, Zhiyuan, Dai, Zhendong
• Format: Article
• Language: English
• Subjects: Abdomen; Adaptability; Adhesion; Adhesives; bio-toe; Climbing; Deformation; Fault tolerance; Fingers & toes; Friction; gecko; Geometry; hierarchical structure; Investigations; Lamellae; Locomotion; Mathematical models; Mechanical properties; Pressure; reversible adhesion; Robots; Silicon wafers; Structure-function relationships; Toe
• ISSN: 2313-7673; 2313-7673
• DOI: 10.3390/biomimetics8010040

The agile locomotion of adhesive animals is mainly attributed to their sophisticated hierarchical feet and reversible adhesion motility. Their structure-function relationship is an urgent issue to be solved to understand biologic adhesive systems and the design of bionic applications. In this study, the reversible adhesion/release behavior and structural properties of gecko toes were investigated, and a hierarchical adhesive bionic toe (bio-toe) consisting of an upper elastic actuator as the supporting/driving layer and lower bionic lamellae (bio-lamellae) as the adhesive layer was designed, which can adhere to and release from targets reversibly when driven by bi-directional pressure. A mathematical model of the nonlinear deformation and a finite element model of the adhesive contact of the bio-toe were developed. Meanwhile, combined with experimental tests, the effects of the structure and actuation on the adhesive behavior and mechanical properties of the bio-toe were investigated. The research found that (1) the bending curvature of the bio-toe, which is approximately linear with pressure, enables the bio-toe to adapt to a wide range of objects controllably; (2) the tabular bio-lamella could achieve a contact rate of 60% with a low squeeze contact of less than 0.5 N despite a ±10° tilt in contact posture; (3) the upward bending of the bio-toe under negative pressure provided sufficient rebounding force for a 100% success rate of release; (4) the ratio of shear adhesion force to preload of the bio-toe with tabular bio-lamellae reaches approximately 12, which is higher than that of most existing adhesion units and frictional gripping units. The bio-toe shows good adaptability, load capacity, and reversibility of adhesion when applied as the basic adhesive unit in a robot gripper and wall-climbing robot. Finally, the proposed reversible adhesive bio-toe with a hierarchical structure has great potential for application in space, defense, industry, and daily life.