Biomechanics of shear-sensitive adhesion in climbing animals: peeling, pre-tension and sliding-induced changes in interface strength

Many arthropods and small vertebrates use adhesive pads for climbing. These biological adhesives have to meet conflicting demands: attachment must be strong and reliable, yet detachment should be fast and effortless. Climbing animals can rapidly and reversibly control their pads' adhesive strength by shear forces, but the mechanisms underlying this coupling have remained unclear. Here, we show that adhesive forces of stick insect pads closely followed the predictions from tape peeling models when shear forces were small, but strongly exceeded them when shear forces were large, resulting in an approximately linear increase of adhesion with friction. Adhesion sharply increased at peel angles less than ca 30°, allowing a rapid switch between attachment and detachment. The departure from classic peeling theory coincided with the appearance of pad sliding, which dramatically increased the peel force via a combination of two mechanisms. First, partial sliding pre-stretched the pads, so that t...诸多节肢动物与小型脊椎动物依靠粘附垫（adhesive pads）实现攀爬。这类生物粘附系统需要满足相互矛盾的性能需求：既要保证粘附牢固可靠，又需实现快速且无需额外费力的脱附。攀爬动物可通过剪切力快速且可逆地调控粘附垫的粘附强度，但其背后的耦合调控机制迄今仍未明晰。本研究表明，当剪切力较小时，竹节虫粘附垫的粘附力与胶带剥离模型的预测结果高度吻合；但当剪切力增大时，其粘附力远超模型预测值，最终导致粘附力随摩擦力呈近似线性增长。当剥离角小于约30°时，粘附力会急剧升高，从而实现粘附与脱附状态间的快速切换。与经典剥离理论的偏离现象，与粘附垫发生滑动的现象同时出现；滑动现象通过两种机制的协同作用，大幅提升了剥离力。首先，部分滑动预先拉伸了粘附垫，进而使得t...