Angle- and Lateral Drag-Dependent Pull-Off Behavior of a Single Gecko Spatula: Insights from a Concurrent Molecular-Continuum Model

Geckos adhere reliably to vertical and inverted surfaces, making them an appealing model for biomimetic adhesives. Yet a complete understanding of how this adhesion works remains elusive, primarily because the underlying mechanisms span multiple length scales. We used a hybrid particle-continuum model to simulate a gecko seta during pull-off tests. We examined how dragging the seta laterally on the substrate, varying drag distance and direction (distal or proximal), and the seta stalk angle influence the pull-off force. Across all conditions, increasing the drag distance raised the pull-off force. This resulted from a reduced peel-off angle before detachment, not from a larger contact area. Higher stalk angles (62° and 72°) also increased adhesion via a lower peel-off angle. Furthermore, distal dragging yielded up to 50% greater pull-off forces than proximal dragging, revealing anisotropic, directionally controllable adhesion. These results clarify how adhesion is tuned and suggest principles for bioinspired, direction-switchable adhesives.