昆虫足的吸附机制

自然界中有许多昆虫足上都有吸附垫,这些垫子经过进化能吸附在各种表面上,并能在运动中控制吸附力。昆虫吸附垫要么是光滑的表皮垫子,要么是密布特殊的刚毛。昆虫这种“飞檐走壁”的能力来自于粘液、复杂机械系统以及生物系统之间的相互作用。文章主要参考国内外研究昆虫吸附机制的文献,综述了能在光滑表面上行走的昆虫的基本爬行原理,对其吸附机制进行了分类。并分析目前研究的主要内容,提出目前昆虫吸附机制要解决的问题。最后对吸附机制在仿生机械应用上作了展望。     

几种直翅目昆虫的形态结构对比

通过解剖实验,对比螽斯科与蟋蟀科在附肢、翅和口器与部分内部系统在构造上的差别,分析螽斯与蟋蟀不同的进化方向。通过对比可知,螽斯科后足不仅较蟋蟀科强壮,并且在前跗节上有着特殊的爪垫,其翅部、口器结构及消化系统也与蟋蟀科有明显区别。通过分析,认为二者在结构上的差异与其栖息环境和食性不同有关,昆虫结构上的微小差异体现了其进化意义及对环境的适应。     

水螅基盘的固着行为及机理的初步研究

采用形态学、组织化学及分子克隆方法对水螅基盘固着行为及相关细胞和分子机理进行了初步研究。研究结果表明,水螅固着时基盘吸附面接近圆形,仅吸附面的圆形周边区域与固着物表面直接接触、而吸附面中央区域不与固着物表面直接接触,并且吸附面周边区域外胚层细胞还沿着固着物表面形成伪足。水螅基盘粘液细胞分子标志物水螅基盘特异性过氧化物酶的表达模式表明粘液细胞在基盘吸附面上不是均匀分布,而仅分布在吸附面的周边区域即吸附面与固着物直接接触的部位。对水螅基盘特异性过氧化物酶氨基酸序列进行生物信息学分析发现该蛋白隐含actin交联因子fascin蛋白的保守结构域,而伪足形成的主要物质基础是细胞质中的actin蛋白分子交联集聚。基盘特异性过氧化物酶可能具有的fascin蛋白活性有助于基盘粘液细胞伪足的形成、从而增强基盘对固着物的吸附力。     

磁修饰酵母对直接大红染料的生物吸附

本研究采用水相合成的纳米级铁磁流体对灭活酿酒酵母细胞进行磁修饰,获得了具有良好磁响应的酵母。傅立叶变换红外光谱分析表明,该修饰酵母在Fe-O特征峰581cm1处的吸收明显加强。透射电镜观察表明,纳米磁性颗粒单个或成团聚集在酵母细胞表面。在本实验条件下,160μL磁修饰酵母对1mL浓度为0.4mg/mL直接大红染料吸附率达100%;8min达到吸附平衡;在70%乙醇中,染料脱吸附率为99.18%。由于磁修饰酵母吸附力强,吸附速度快,易于磁分离,是一种有前景的水溶性染料生物吸附剂。     

固定甘氨酸用于吸附水中金属离子的研究

采用环氧氯丙烷法将惰性载体Sephadex G-25活化,使其与甘氨酸偶联从而得到固定羧基的离子交换吸附剂。对该吸附剂吸附金属离子性能的研究表明,在pH 9.0时,吸附剂对Ca2+等金属离子有很强的吸附,且对Fe2+、Fe3+、Mn2+的吸附力比对Ca2+和Mg2+的吸附力要强。16g(湿重)吸附剂对金属离子的饱和吸附量分别为:Ca2+16.99mg,Mg2+6.86mg,Fe2+10.06mg,Fe3+4.93mg,Mn2+11.51mg。同时,该吸附剂具有稳定性好、能重复使用且制备成本低等特点,在污水处理、金属离子回收等方面有很好的应用前景。     

微生物在矿物表面吸附的研究进展

微生物在矿物表面的吸附是微生物与矿物表面深度作用的前提, 也是生物药剂在选矿中的应用的基础研究。本文综述了影响微生物在矿物表面吸附的环境因素, 微生物细胞与矿物表面之间的相互作用, 微生物细胞表面基团、表面成分及其胞外聚合物对吸附过程的影响, 并提出了今后的研究方向。     

吸附树脂分离纯化高麦芽糖浆的研究

本文提出并研究了吸附树脂分离纯化提高麦芽糖浆的新工艺,选出了较适合的吸附树脂进行了交换柱吸附分离提纯及其再生方法试验。结果表明,ＷＩ树脂对超高麦芽糖浆中的低聚糖具有较好的吸附分离效果。在交换柱中进行吸附分离试验时,单批处理量为０．６７ｍｌ／ｇ树脂时,ＷＩ吸附低聚为９１．０％以上。     

絮凝酵母吸附Cr(VI)的机理

絮凝酵母SPSC01为酿酒酵母Saccharomyces cerevisiae和粟酒裂殖酵母Schizosaccharomyces pombe的融合菌株,用其吸附水溶液中的重金属Cr(VI),可以大大降低生物吸附的固液分离成本。为了探讨SPSC01菌体絮凝蛋白对Cr(VI)还原吸附的影响,对SPSC01与其亲本菌株的吸附行为进行了比较。结果表明,SPSC01和其具有絮凝性状的亲本S.pombe的Cr(VI)去除速率基本同步,远优于无絮凝性状的亲本S.cerevisiae;达到吸附平衡时,S.pombe、SPSC01和S.cerevisiae对总Cr去除率分别达68.8%、48.6%和37.5%;从而证明了絮凝有利于Cr(VI)的还原、吸附,絮凝蛋白在Cr(VI)的还原吸附过程中起促进作用。通过化学屏蔽方法和傅立叶变换红外光谱(FTIR)分析,对SPSC01菌体表面吸附Cr(VI)的机理进行了研究,结果表明SPSC01菌体表面吸附Cr(VI)起主要作用的基团是氨基、羧基和酰胺基。     

絮凝酵母吸附Cr(VI) 的机理

絮凝酵母SPSC01为酿酒酵母Saccharomyces cerevisiae和粟酒裂殖酵母Schizosaccharomyces pombe的融合菌株,用其吸附水溶液中的重金属Cr(VI),可以大大降低生物吸附的固液分离成本。为了探讨SPSC01菌体絮凝蛋白对Cr(VI) 还原吸附的影响,对SPSC01与其亲本菌株的吸附行为进行了比较。结果表明,SPSC01和其具有絮凝性状的亲本S. pombe的Cr(VI) 去除速率基本同步,远优于无絮凝性状的亲本S. cerevisiae;达到吸附平衡时,S. pombe、SPSC01和S. cerevisiae对总Cr去除率分别达68.8％、48.6％和37.5％;从而证明了絮凝有利于Cr(VI) 的还原、吸附,絮凝蛋白在Cr(VI) 的还原吸附过程中起促进作用。通过化学屏蔽方法和傅立叶变换红外光谱 (FTIR) 分析,对SPSC01菌体表面吸附Cr(VI) 的机理进行了研究,结果表明SPSC01菌体表面吸附Cr(VI) 起主要作用的基团是氨基、羧基和酰胺基。     

消杀型纳米催化剂抗病毒作用的研究

本文探讨112种消杀型纳米催化剂吸附与灭活病毒的功效,为开发新型抗病毒纳米材料提供理论依据。我们将各种纳米催化剂与副流感病毒、人疱疹病毒Ⅰ型、腺病毒1型及5型作用一定时间后,分别以血凝试验及观察CPE变化的方法判断纳米材料对各种病毒的吸附与灭活作用,并在电子显微镜下观察纳米材料对病毒的吸附情况。结果在所检测的112种纳米催化剂中,用血凝试验分别筛选出强吸附力催化剂 29 种、中吸附力催化剂 36 种、弱吸附力催化剂47种。其中,13 种强吸附力催化剂对副流感病毒的吸附率在 87.5%~93.75%之间,并以 AB 24的抗病毒效果最好。     

Biomechanics of smooth adhesive pads in insects: influence of tarsal secretion on attachment performance

Many insects possess smooth adhesive pads on their legs, which adhere by thin films of a two-phasic secretion. To understand the function of such fluid-based adhesive systems, we simultaneously measured adhesion, friction and contact area in single pads of stick insects (Carausius morosus). Shear stress was largely independent of normal force and increased with velocity, seemingly consistent with the viscosity-effect of a continuous fluid film. However, measurements of the remaining force 2 min after a sliding movement show that adhesive pads can sustain considerable static friction. Repeated sliding movements and multiple consecutive pull-offs to deplete adhesive secretion showed that on a smooth surface, friction and adhesion strongly increased with decreasing amount of fluid. In contrast, pull-off forces significantly decreased on a rough substrate. Thus, the secretion does not generally increase attachment but does so only on rough substrates, where it helps to maximize contact area. When slides were repeated at one position so that secretion could accumulate, sliding shear stress decreased but static friction remained clearly present. This suggests that static friction which is biologically important to prevent sliding is based on non-Newtonian properties of the adhesive emulsion rather than on a direct contact between the cuticle and the substrate.     

Functionally Different Pads on the Same Foot Allow Control of Attachment: Stick Insects Have Load-Sensitive “Heel” Pads for Friction and Shear-Sensitive “Toe” Pads for Adhesion

Stick insects (Carausius morosus) have two distinct types of attachment pad per leg, tarsal “heel” pads (euplantulae) and a pre-tarsal “toe” pad (arolium). Here we show that these two pad types are specialised for fundamentally different functions. When standing upright, stick insects rested on their proximal euplantulae, while arolia were the only pads in surface contact when hanging upside down. Single-pad force measurements showed that the adhesion of euplantulae was extremely small, but friction forces strongly increased with normal load and coefficients of friction were 1. The pre-tarsal arolium, in contrast, generated adhesion that strongly increased with pulling forces, allowing adhesion to be activated and deactivated by shear forces, which can be produced actively, or passively as a result of the insects'' sprawled posture. The shear-sensitivity of the arolium was present even when corrected for contact area, and was independent of normal preloads covering nearly an order of magnitude. Attachment of both heel and toe pads is thus activated partly by the forces that arise passively in the situations in which they are used by the insects, ensuring safe attachment. Our results suggest that stick insect euplantulae are specialised “friction pads” that produce traction when pressed against the substrate, while arolia are “true” adhesive pads that stick to the substrate when activated by pulling forces.     

Friction ridges in cockroach climbing pads: anisotropy of shear stress measured on transparent,microstructured substrates

The contact of adhesive structures to rough surfaces has been difficult to investigate as rough surfaces are usually irregular and opaque. Here we use transparent, microstructured surfaces to investigate the performance of tarsal euplantulae in cockroaches (Nauphoeta cinerea). These pads are mainly used for generating pushing forces away from the body. Despite this biological function, shear stress (force per unit area) measurements in immobilized pads showed no significant difference between pushing and pulling on smooth surfaces and on 1-μm high microstructured substrates, where pads made full contact. In contrast, on 4-μm high microstructured substrates, where pads made contact only to the top of the microstructures, shear stress was maximal during a push. This specific direction dependence is explained by the interlocking of the microstructures with nanometre-sized “friction ridges” on the euplantulae. Scanning electron microscopy and atomic force microscopy revealed that these ridges are anisotropic, with steep slopes facing distally and shallow slopes proximally. The absence of a significant direction dependence on smooth and 1-μm high microstructured surfaces suggests the effect of interlocking is masked by the stronger influence of adhesion on friction, which acts equally in both directions. Our findings show that cockroach euplantulae generate friction using both interlocking and adhesion.     

Whole animal measurements of shear and adhesive forces in adult tree frogs: insights into underlying mechanisms of adhesion obtained from studying the effects of size and scale

This allometric study of adhesion in 15 Trinidadian tree frog species investigates how relationships between length, area and mass limit the ability of adult frog species of different sizes to adhere to inclined and overhanging surfaces. Our experiments show that hylid frogs possess an area-based wet adhesive system in which larger species are lighter than expected from isometry and adhere better than expected from their toe pad area. However, in spite of these adaptations, larger species adhere less well than smaller species. In addition to these adhesive forces, tree frogs also generate significant shear forces that scale with mass, suggesting that they are frictional forces. Toe pads detach by peeling and frogs have strategies to prevent peeling from taking place while they are adhering to surfaces, including orienting themselves head-up on slopes. The scaling of tree frog adhesion is also used to distinguish between different models for adhesion, including classic formulae for capillarity and Stefan adhesion. These classic equations grossly overestimate the adhesive forces that tree frogs produce. More promising are peeling models, designed to predict the pull-off forces of adhesive tape. However, more work is required before we can qualitatively and quantitatively describe the adhesive mechanism of tree frogs.     

Pushing versus pulling: division of labour between tarsal attachment pads in cockroaches

Adhesive organs on the legs of arthropods and vertebrates are strongly direction dependent, making contact only when pulled towards the body but detaching when pushed away from it. Here we show that the two types of attachment pads found in cockroaches (Nauphoeta cinerea), tarsal euplantulae and pretarsal arolium, serve fundamentally different functions. Video recordings of vertical climbing revealed that euplantulae are almost exclusively engaged with the substrate when legs are pushing, whereas arolia make contact when pulling. Thus, upward-climbing cockroaches used front leg arolia and hind leg euplantulae, whereas hind leg arolia and front leg euplantulae were engaged during downward climbing. Single-leg friction force measurements showed that the arolium and euplantulae have an opposite direction dependence. Euplantulae achieved maximum friction when pushed distally, whereas arolium forces were maximal during proximal pulls. This direction dependence was not explained by the variation of shear stress but by different contact areas during pushing or pulling. The changes in contact area result from the arrangement of the flexible tarsal chain, tending to detach the arolium when pushing and to peel off euplantulae when in tension. Our results suggest that the euplantulae in cockroaches are not adhesive organs but 'friction pads', mainly providing the necessary traction during locomotion.     

An integrative study of insect adhesion: mechanics and wet adhesion of pretarsal pads in ants

Many animals that locomote by legs possess adhesive pads. Suchorgans are rapidly releasable and adhesive forces can be controlledduring walking and running. This capacity results from the interactionof adhesive with complex mechanical systems. Here we presentan integrative study of the mechanics and adhesion of smoothattachment pads (arolia) in Asian Weaver ants (Oecophylla smaragdina).Arolia can be unfolded and folded back with each step. Theyare extended either actively by contraction of the claw flexormuscle or passively when legs are pulled toward the body. Regulationof arolium use and surface attachment includes purely mechanicalcontrol inherent in the arrangement of the claw flexor system. Predictions derived from a ‘wet’ adhesion mechanismwere tested by measuring attachment forces on a smooth surfaceusing a centrifuge technique. Consistent with the behavior ofa viscid secretion, frictional forces per unit contact arealinearly increased with sliding velocity and the increment stronglydecreased with temperature. We studied the nature and dimensions of the adhesive liquidfilm using Interference Reflection Microscopy (IRM). Analysisof ‘footprint’ droplets showed that they are hydrophobicand form low contact angles. In vivo IRM of insect pads in contactwith glass, however, revealed that the adhesive liquid filmnot only consists of a hydrophobic fluid, but also of a volatile,hydrophilic phase. IRM allows estimation of the height of theliquid film and its viscosity. Preliminary data indicate thatthe adhesive secretion alone is insufficient to explain theobserved friction and that rubbery deformation of the pad cuticleis involved.     

Effect of Microscale Contact State of Polyurethane Surface on Adhesion and Friction

The effect of microscale contact of rough surfaces on the adhesion and friction under negative normal forces was experimentally investigated. The adhesive force of single point contact - sapphire ball to flat polyurethane did not vary with the normal force. With rough surface contact, which was assumed to be a great number of point contacts, the adhesive force increased logarithmically with the normal force. Under negative normal force adhesive state, the tangential force （more than hundred mN） were much larger than the negative normal force （several mN） and increased with the linear decrease of negative normal force. The results reveal why the gecko＇s toe must slide slightly on the target surface when it makes contact on a surface and suggest how a biomimetic gecko foot might be designed.     

Arachnids secrete a fluid over their adhesive pads

Background

Many arachnids possess adhesive pads on their feet that help them climb smooth surfaces and capture prey. Spider and gecko adhesives have converged on a branched, hairy structure, which theoretically allows them to adhere solely by dry (solid-solid) intermolecular interactions. Indeed, the consensus in the literature is that spiders and their smooth-padded relatives, the solifugids, adhere without the aid of a secretion.

Methodology and Principal Findings

We investigated the adhesive contact zone of living spiders, solifugids and mites using interference reflection microscopy, which allows the detection of thin liquid films. Like insects, all the arachnids we studied left behind hydrophobic fluid footprints on glass (mean refractive index: 1.48–1.50; contact angle: 3.7–11.2°). Fluid was not always secreted continuously, suggesting that pads can function in both wet and dry modes. We measured the attachment forces of single adhesive setae from tarantulas (Grammostola rosea) by attaching them to a bending beam with a known spring constant and filming the resulting deflection. Individual spider setae showed a lower static friction at rest (26%±2.8 SE of the peak friction) than single gecko setae (Thecadactylus rapicauda; 96%±1.7 SE). This may be explained by the fact that spider setae continued to release fluid after isolation from the animal, lubricating the contact zone.

Significance

This finding implies that tarsal secretions occur within all major groups of terrestrial arthropods with adhesive pads. The presence of liquid in an adhesive contact zone has important consequences for attachment performance, improving adhesion to rough surfaces and introducing rate-dependent effects. Our results leave geckos and anoles as the only known representatives of truly dry adhesive pads in nature. Engineers seeking biological inspiration for synthetic adhesives should consider whether model species with fluid secretions are appropriate to their design goals.     

Adhesive and frictional properties of tarsal attachment pads in two species of stick insects (Phasmatodea) with smooth and nubby euplantulae

In the present study, the tarsal attachment pads (euplantulae) of two stick insect species (Phasmatodea) were compared. While the euplantulae of Cuniculina impigra (syn. Medauroidea extradentata) are smooth, those of Carausius morosus bear small nubs on their surfaces. In order to characterize the adhesive and frictional properties of both types of euplantulae, adhesion and friction measurements on smooth (Ra=0.054 μm) and rough (Ra=1.399 μm) substrates were carried out. The smooth pads of C. impigra generated stronger adhesion on the smooth substrate than on the rough one. The adhesive forces of the structured pads of C. morosus did not differ between the two substrates. Friction experiments showed anisotropy for both species with higher values for proximal pulls than for distal pushes. In C. impigra, friction was stronger on the smooth than on the rough surface for both directions, whereas in C. morosus friction was stronger on the smooth surface only for pushes. This shows that smooth attachment pads are able to generate relatively stronger adhesion and friction on a flat smooth surface than on a rough one. In contrast, nubby pads have similar adhesion on both substrates, and also show no difference in friction in the pulling direction. This leads to the conclusion that smooth pads are specialized for rather smooth substrates, whereas nubby pads are better adapted to generate stronger forces on a broader range of surfaces.     

Adhesive Contact in Animal: Morphology, Mechanism and Bio-Inspired Application

Many animals possess adhesive pads on their feet,which are able to attach to various substrates while controlling adhesive forces during locomotion.This review article studies the morphology of adhesive devices in animals,and the physical mechanisms of wet adhesion and dry adhesion.The adhesive pads are either ‘smooth' or densely covered with special adhesive setae.Smooth pads adhere by wet adhesion,which is facilitated by fluid secreted from the pads,whereas hairy pads can adhere by dry adhesion or wet adhesion.Contact area,distance between pad and substrate,viscosity and surface tension of the liquid filling the gap between pad and substrate are the most important factors which determine the wet adhesion.Dry adhesion was found only in hairy pads,which occurs in geckos and spiders.It was demonstrated that van der Waals interaction is the dominant adhesive force in geckos' adhesion.The bio-inspired applications derived from adhesive pads are also reviewed.