Büscher Thies H, Gorb Stanislav N
Department of Functional Morphology and Biomechanics, Institute of Zoology, Kiel University, Am Botanischen Garten 9, 24118 Kiel, Germany.
Beilstein J Nanotechnol. 2021 Jul 15;12:725-743. doi: 10.3762/bjnano.12.57. eCollection 2021.
Adhesive pads are functional systems with specific micro- and nanostructures which evolved as a response to specific environmental conditions and therefore exhibit convergent traits. The functional constraints that shape systems for the attachment to a surface are general requirements. Different strategies to solve similar problems often follow similar physical principles, hence, the morphology of attachment devices is affected by physical constraints. This resulted in two main types of attachment devices in animals: hairy and smooth. They differ in morphology and ultrastructure but achieve mechanical adaptation to substrates with different roughness and maximise the actual contact area with them. Species-specific environmental surface conditions resulted in different solutions for the specific ecological surroundings of different animals. As the conditions are similar in discrete environments unrelated to the group of animals, the micro- and nanostructural adaptations of the attachment systems of different animal groups reveal similar mechanisms. Consequently, similar attachment organs evolved in a convergent manner and different attachment solutions can occur within closely related lineages. In this review, we present a summary of the literature on structural and functional principles of attachment pads with a special focus on insects, describe micro- and nanostructures, surface patterns, origin of different pads and their evolution, discuss the material properties (elasticity, viscoelasticity, adhesion, friction) and basic physical forces contributing to adhesion, show the influence of different factors, such as substrate roughness and pad stiffness, on contact forces, and review the chemical composition of pad fluids, which is an important component of an adhesive function. Attachment systems are omnipresent in animals. We show parallel evolution of attachment structures on micro- and nanoscales at different phylogenetic levels, focus on insects as the largest animal group on earth, and subsequently zoom into the attachment pads of the stick and leaf insects (Phasmatodea) to explore convergent evolution of attachment pads at even smaller scales. Since convergent events might be potentially interesting for engineers as a kind of optimal solution by nature, the biomimetic implications of the discussed results are briefly presented.
粘附垫是具有特定微观和纳米结构的功能系统，它们是对特定环境条件的一种进化响应，因此呈现出趋同特征。形成附着于表面的系统的功能限制是普遍要求。解决类似问题的不同策略通常遵循相似的物理原理，因此，附着装置的形态受到物理限制的影响。这导致动物中主要有两种附着装置类型：有毛的和光滑的。它们在形态和超微结构上有所不同，但都能实现对不同粗糙度底物的机械适应，并使其与底物的实际接触面积最大化。特定物种的环境表面条件导致了针对不同动物特定生态环境的不同解决方案。由于在与动物群体无关的离散环境中条件相似，不同动物群体附着系统的微观和纳米结构适应性揭示了相似的机制。因此，相似的附着器官以趋同的方式进化，并且在密切相关的谱系中可能出现不同的附着解决方案。在这篇综述中，我们总结了关于附着垫结构和功能原理的文献，特别关注昆虫，描述微观和纳米结构、表面图案、不同垫的起源及其进化，讨论有助于粘附的材料特性（弹性、粘弹性、粘附力、摩擦力）和基本物理力，展示不同因素（如底物粗糙度和垫的刚度）对接触力的影响，并综述垫液的化学成分，这是粘附功能的一个重要组成部分。附着系统在动物中无处不在。我们展示了在不同系统发育水平上微观和纳米尺度附着结构的平行进化，将重点放在地球上最大的动物群体昆虫上，随后深入研究竹节虫和叶虫（竹节虫目）的附着垫，以探索更小尺度上附着垫的趋同进化。由于趋同事件作为一种自然的最优解决方案可能对工程师有潜在的吸引力，我们简要介绍了所讨论结果的仿生意义。
