Data from: Insect adhesion on rough surfaces: analysis of adhesive contact of smooth and hairy pads on transparent micro-structured substrates

Insect climbing footpads are able to adhere to rough surfaces, but the details of this capability are still unclear. To overcome experimental limitations of randomly rough, opaque surfaces, we fabricated transparent test substrates containing square arrays of 1.4 µm diameter pillars, with variable height (0.5 and 1.4 µm) and spacing (from 3 to 22 µm). Smooth pads of cockroaches (Nauphoeta cinerea) made partial contact (limited to the tops of the structures) for the two densest arrays of tall pillars, but full contact (touching the substrate in between pillars) for larger spacings. The transition from partial to full contact was accompanied by a sharp increase in shear forces. Tests on hairy pads of dock beetles (Gastrophysa viridula) showed that setae adhered between pillars for larger spacings, but pads were equally unable to make full contact on the densest arrays. The beetles' shear forces similarly decreased for denser arrays, but also for short pillars and with a more gradual transition. These observations can be explained by simple contact models derived for soft uniform materials (smooth pads) or thin flat plates (hairy-pad spatulae). Our results show that microstructured substrates are powerful tools to reveal adaptations of natural adhesives for rough surfaces.

昆虫攀附足垫可附着于粗糙表面，但该能力的详细作用机制仍未阐明。为突破随机粗糙不透明表面带来的实验限制，我们制备了搭载方形阵列微柱的透明测试基底：微柱直径为1.4 μm，高度分为0.5 μm与1.4 μm两种，间距可调范围为3 μm至22 μm。针对灰斑扁蠊（*Nauphoeta cinerea*）的光滑足垫测试显示，在两组最密集的高微柱阵列上，足垫仅能实现部分接触（仅与微柱顶端接触）；而当微柱间距增大时，足垫则可实现完全接触（同时与微柱间的基底表面发生接触）。从部分接触到完全接触的转变过程，伴随剪切力的急剧上升。针对绿毛叶甲（*Gastrophysa viridula*）的多毛足垫测试表明，当微柱间距增大时，其刚毛可与微柱间的基底表面发生附着，但在最密集的微柱阵列上，足垫同样无法实现完全接触。随着微柱阵列密度升高，叶甲的剪切力同样会下降；微柱高度较低时，剪切力也会下降，且接触状态的转变过程更为平缓。上述观测结果可通过针对软均质材料（对应光滑足垫）或薄平板（对应多毛足垫的铲状刚毛末端）推导得到的简易接触模型加以解释。本研究结果证实，微结构基底是揭示粗糙表面适配型天然黏附系统的高效研究工具。