Biomaterials: silk-like secretion from tarantula feet

An unsuspected attachment mechanism may help these huge spiders to avoid catastrophic falls. Spiders spin silk from specialized structures known as abdominal spinnerets--a defining feature of the creatures--and this is deployed to capture prey, protect themselves, reproduce and disperse. Here we show that zebra tarantulas (Aphonopelma seemanni) from Costa Rica also secrete silk from their feet to provide adhesion during locomotion, enabling these spiders to cling to smooth vertical surfaces. Our discovery that silk is produced by the feet provides a new perspective on the origin and diversification of spider silk.     

The morphological and functional variability of pleon-holding mechanisms in selected Eubrachyura (Crustacea: Decapoda)

Eubrachyurans not only exhibit a crab-like body shape, consisting of a mostly wide cephalothorax and a thin, shield-like pleon folded underneath it, but reportedly hold the pleon in this position with the use of specialized holding structures. To further our knowledge of the variability of these holding structures, and investigate their functionality, male and female crabs from five primary freshwater crab and five selected thoracotreme families were examined with stereomicroscopy. Exemplary specimens of each group were documented photographically and with micro-computed tomography to illustrate the holding structures in situ. The results show a press-button mechanism of variable shape in freshwater crabs, where divergent structures possibly support pleon attachment of different effectiveness. The press-button is present in the majority of basal heterotreme lineages, and is therefore regarded as an ancestral character of the Heterotremata. In the Thoracotremata, multiple holding mechanisms are identified: press-button, clasping apparatus, overhanging edge, and increased setae cover on sternal plates, with the last system probably only effective in terrestrial species, due to wet adhesion effects. The ancestral character state in the Thoracotremata is debatable, but most likely also a functional press-button was present. Each holding mechanism requires different pleon movements to engage and disengage. Additionally, in contrast to the most common press-button mechanism, divergent holding mechanisms tend to be present, and likely functional, in adult males and females.     

Contact mechanics of pad of grasshopper (Insecta: ORTHOPTERA) by finite element methods

During locomotion, insect feet endure dramatic impact force and generate adhesive force which is controlled by the architecture of the foot. The patterns of smooth attachment pads in insect feet vary widely among insect orders and families. The functional significance of the micro-structure and geometric design of insect feet remains largely unknown. In this study, we developed a two-dimensional finite element model of a grasshopper’s attachment pad. Realistic geometric microstructure and material propertie...     

蝗虫脚掌微结构及其接触的有限元分析

用电子显微镜研究了蝗虫足掌的微结构，用非线性有限元方法分析足掌接触过程的变形规律、接触刚度及接触面积、气囊的作用和足掌的应力应变规律．结果表明，蝗虫足掌以软性外表皮包含血浆(液体)的结构形式，有利于降低接触刚度、增加接触面积，并使爪垫在接触过程便产生有利于稳定附着的摩擦力．软性外表皮内的树丛状杆组织结构会提高足掌在各种表面上的适应性，降低足掌内部的应力．     

聚氨酯粘着性能的实验研究

用生物摩擦学实验系统研究聚氨酯材料的化学成分、试样连接刚度、试样间初始接触角等在不同法向载荷的粘着性能。结果表明，聚氨酯的化学成分对其粘着性能有重要影响，在多羟基化合物与MDI(二异氰酸酯)的组分比为1：2时，粘着力最大。连接刚度是影响粘着性能的另一主要因素。软连接情况下，不同接触角时，同样粗糙的表面上，材料的粘着性能相差不大。不同粗糙度的表面间的粘着力差异显著。刚性连接情况下，粘着力随接触角的增加而减小。在较光滑表面上降低的幅度大于粗糙表面上的幅度。上述实验结果为仿生足掌的设计提供了重要数据。