Department of Bioengineering, Imperial College London, London SW7 2AZ, UK.
J R Soc Interface. 2022 Jun;19(191):20220212. doi: 10.1098/rsif.2022.0212. Epub 2022 Jun 22.
Many insects use adhesive organs to climb. The ability to cling to surfaces is advantageous but is increasingly challenged as animals grow, due to the associated reduction in surface-to-volume ratio. Previous work has demonstrated that some climbing animals overcome this scaling problem by systematically altering the maximum force per area that their adhesive pads can sustain; their adhesive organs become more efficient as they grow, an observation which is also of substantial relevance for the design of bioinspired adhesives. What is the origin of this change in efficiency? In insects, adhesive contact is mediated by a thin film of a liquid, thought to increase adhesive performance via capillary and viscous forces. Here, we use interference reflection microscopy and dewetting experiments to measure the contact angle and dewetting speed of the secretion of pre-tarsal adhesive pads of Indian stick insects, varying in mass by over two orders of magnitude. Neither contact angle nor dewetting speed change significantly with body mass, suggesting that the key physical properties of the pad secretion-its surface tension and viscosity-are size-invariant. Thus, the observed change in pad efficiency is unlikely to arise from systematic changes of the physical properties of the pad secretion; the functional role of the secretion remains unclear.
许多昆虫使用粘性器官来攀爬。附着表面的能力是有利的，但随着动物的生长，由于表面积与体积比的相关减少，这种能力越来越受到挑战。以前的工作表明，一些攀爬动物通过系统地改变其粘性垫能够承受的单位面积最大力来克服这个比例问题；随着它们的生长，它们的粘性器官变得更有效率，这一观察结果对于仿生粘合剂的设计也具有重要意义。这种效率变化的起源是什么？在昆虫中，粘性接触是由一层薄的液体介导的，据认为这种液体通过毛细作用力和粘性力来提高粘性性能。在这里，我们使用干涉反射显微镜和去湿实验来测量印度竹节虫前跗节粘性垫分泌物的接触角和去湿速度，这些分泌物的质量相差两个数量级以上。接触角和去湿速度都没有随体重显著变化，这表明垫分泌物的关键物理性质——表面张力和粘度——是不变的。因此，观察到的垫效率的变化不太可能是由于垫分泌物的物理性质的系统变化引起的；分泌物的功能作用仍不清楚。
