Synopsis The adhesive toe pads of tree frogs have inspired the design of various so-called ‘smooth’ synthetic adhesives for wet environments. However, these adhesives do not reach the attachment performance of their biological models in terms of contact formation, maintenance of attachment, and detachment. In tree frogs, attachment is facilitated by an interconnected ensemble of superficial and internal morphological components, which together form a functional unit. To help bridging the gap between biological and bioinspired adhesives, in this review, we (1) provide an overview of the functional components of tree frog toe pads, (2) investigate which of these components (and attachment mechanisms implemented therein) have already been transferred into synthetic adhesives, and (3) highlight functional analogies between existing synthetic adhesives and tree frogs regarding the fundamental mechanisms of attachment. We found that most existing tree-frog-inspired adhesives mimic the micropatterned surface of the ventral epidermis of frog pads. Geometrical and material properties differ between these synthetic adhesives and their biological model, which indicates similarity in appearance rather than function. Important internal functional components such as fiber-reinforcement and muscle fibers for attachment control have not been considered in the design of tree-frog-inspired adhesives. Experimental work on tree-frog-inspired adhesives suggests that the micropatterning of adhesives with low-aspect-ratio pillars enables crack arresting and the drainage of interstitial liquids, which both facilitate the generation of van der Waals forces. Our analysis of experimental work on tree-frog-inspired adhesives indicates that interstitial liquids such as the mucus secreted by tree frogs play a role in detachment. Based on these findings, we provide suggestions for the future design of biomimetic adhesives. Specifically, we propose to implement internal fiber-reinforcements inspired by the fibrous structures in frog pads to create mechanically reinforced soft adhesives for high-load applications. Contractile components may stimulate the design of actuated synthetic adhesives with fine-tunable control of attachment strength. An integrative approach is needed for the design of tree-frog-inspired adhesives that are functionally analogous with their biological paradigm.

中文翻译：

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树蛙胶粘剂的设计

概要 树蛙的粘性脚趾垫启发了各种用于潮湿环境的所谓“光滑”合成粘合剂的设计。然而，这些粘合剂在接触形成、附着保持和分离方面没有达到其生物模型的附着性能。在树蛙中，附着是由表面和内部形态成分相互连接的整体促进的，它们共同形成一个功能单元。为了帮助弥合生物粘合剂和仿生粘合剂之间的差距，在本次审查中，我们 (1) 概述了树蛙脚趾垫的功能组件，(2) 调查这些组件中的哪些（以及其中实施的连接机制）已经被转移到合成粘合剂中，(3) 强调现有合成粘合剂和树蛙之间在附着的基本机制方面的功能类比。我们发现大多数现有的受树蛙启发的粘合剂模仿青蛙垫腹侧表皮的微图案表面。这些合成粘合剂与其生物模型之间的几何和材料特性不同，这表明外观相似，而不是功能相似。受树蛙启发的粘合剂的设计中没有考虑重要的内部功能组件，例如用于附着控制的纤维增强和肌肉纤维。对受树蛙启发的粘合剂的实验工作表明，具有低纵横比支柱的粘合剂的微图案化能够阻止裂缝并排出间隙液体，这两者都促进了范德瓦尔斯力的产生。我们对受树蛙启发的粘合剂的实验工作的分析表明，树蛙分泌的粘液等间隙液体在分离中起作用。基于这些发现，我们为仿生粘合剂的未来设计提供了建议。具体而言，我们建议实施受青蛙垫中纤维结构启发的内部纤维增强材料，以创建用于高负载应用的机械增强软粘合剂。可收缩组件可以通过对附着强度的微调控制来刺激驱动合成粘合剂的设计。需要一种综合方法来设计在功能上与其生物学范式类似的受树蛙启发的粘合剂。我们对受树蛙启发的粘合剂的实验工作的分析表明，树蛙分泌的粘液等间隙液体在分离中起作用。基于这些发现，我们为仿生粘合剂的未来设计提供了建议。具体而言，我们建议实施受青蛙垫中纤维结构启发的内部纤维增强材料，以创建用于高负载应用的机械增强软粘合剂。可收缩组件可以通过对附着强度的微调控制来刺激驱动合成粘合剂的设计。需要一种综合方法来设计在功能上与其生物学范式类似的受树蛙启发的粘合剂。我们对受树蛙启发的粘合剂的实验工作的分析表明，树蛙分泌的粘液等间隙液体在分离中起作用。基于这些发现，我们为仿生粘合剂的未来设计提供了建议。具体而言，我们建议实施受青蛙垫中纤维结构启发的内部纤维增强材料，以创建用于高负载应用的机械增强软粘合剂。可收缩组件可以通过对附着强度的微调控制来刺激驱动合成粘合剂的设计。需要一种综合方法来设计在功能上与其生物学范式类似的受树蛙启发的粘合剂。基于这些发现，我们为仿生粘合剂的未来设计提供了建议。具体而言，我们建议实施受青蛙垫中纤维结构启发的内部纤维增强材料，以创建用于高负载应用的机械增强软粘合剂。可收缩组件可以通过对附着强度的微调控制来刺激驱动合成粘合剂的设计。需要一种综合方法来设计在功能上与其生物学范式类似的受树蛙启发的粘合剂。基于这些发现，我们为仿生粘合剂的未来设计提供了建议。具体而言，我们建议实施受青蛙垫中纤维结构启发的内部纤维增强材料，以创建用于高负载应用的机械增强软粘合剂。可收缩组件可以通过对附着强度的微调控制来刺激驱动合成粘合剂的设计。需要一种综合方法来设计在功能上与其生物学范式类似的受树蛙启发的粘合剂。可收缩组件可以通过对附着强度的微调控制来刺激驱动合成粘合剂的设计。需要一种综合方法来设计在功能上与其生物学范式类似的受树蛙启发的粘合剂。可收缩组件可以通过对附着强度的微调控制来刺激驱动合成粘合剂的设计。需要一种综合方法来设计在功能上与其生物学范式类似的受树蛙启发的粘合剂。