Spatulate structures in biological fibrillar adhesion

To provide an explanation of why most biological hairy adhesive systems involved in locomotion rely on spatulate structures, we have studied the contact formed between a smooth substrate and individual thin-film terminal elements of attachment pads evolved in insects, arachnids and reptiles. The data obtained were analyzed using the Kendall peeling model, which demonstrated that an animal's attachment ability grows with an overall length of the peeling line, which is the sum of widths of all thin-film elements participating in contact. This robust principle is found to manifest itself across 8 orders of magnitude in an overall peeling line ranging from 64 micrometres for a red spider mite to 1.8 kilometres for a Tokay gecko, generalizing the critical role of terminal elements in biological fibrillar adhesion.