Designing Bio-Inspired Adhesives for Shear Loading: From Simple Structures to Complex Patterns

The gecko has inspired numerous synthetic adhesive structures, yet under shear loading conditions, general design criteria remains underdeveloped. To provide guidance for bio-inspired adhesives under shear, a simple scaling theory is used to investigate the relevant geometric and material parameters. The total compliance of an elastic attachment feature is described over many orders of magnitude in aspect ratio through a single continuous function using the superposition of multiple deformation modes such as bending, shear deformation, and tensile elongation. This allows for force capacity predictions of common geometric control parameters such as thickness, aspect ratio, and contact area. This superposition principal is extended to develop criteria for patterned interfaces under shear loading. Importantly, the adhesive patterns under shear are controlled through the compliance in the direction of loading. These predictions are confirmed experimentally using macroscopic building blocks over an extensive range of aspect ratio and contact area. Over 25 simple and complex patterns with various contact geometries are examined, and the effect of geometry and material properties on the shear adhesion behavior is discussed. Furthermore, all of these various attachment features are described with a single scaling parameter, offering control over orders of magnitude in adhesive force capacity for a variety of applications.