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.     

Use of biorobotic models of highly deformable fins for studying the mechanics and control of fin forces in fishes

Bony fish swim with a level of agility that is unmatched in human-developed systems. This is due, in part, to the ability of the fish to carefully control hydrodynamic forces through the active modulation of the fins' kinematics and mechanical properties. To better understand how fish produce and control forces, biorobotic models of the bluegill sunfish's (Lepomis macrochirus) caudal fin and pectoral fins were developed. The designs of these systems were based on detailed analyses of the anatomy, kinematics, and hydrodynamics of the biological fins. The fin models have been used to investigate how fin kinematics and the mechanical properties of the fin-rays influence propulsive forces and to explore kinematic patterns that were inspired by biological motions but that were not explicitly performed by the fish. Results from studies conducted with the fin models indicate that subtle changes to the kinematics and mechanical properties of fin rays can significantly impact the magnitude, direction, and time course of the 3D forces used for propulsion and maneuvers. The magnitude of the force tends to scale with the fin's stiffness, but the direction of the force is not invariant, and this causes disproportional changes in the magnitude of the thrust, lift, and lateral components of force. Results from these studies shed light on the multiple strategies that are available to the fish to modulate fin forces.     

Evolution of locomotory attachment pads in the Dermaptera (Insecta)

This contribution is the first comparative SEM study of tarsal and pretarsal structures of 18 dermapteran species, including epizoic Hemimeridae, rare Apachyidae, as well as basal Pygidicranidae. Our data reject the apparent uniformity of this taxon and show that representatives of Dermaptera have independently evolved both types of attachment mechanisms: hairy and smooth. Dermaptera possess a wide spectrum of attachment devices: arolia, euplantulae, tarsal surfaces covered with specialised tenent setae and other types of cuticular outgrowths. The groundpattern of the pretarsal and tarsal attachment structures was reconstructed by mapping their characters onto a cladogram, generated without tarsal characters. In the groundpattern of recent Dermaptera, the tarsus consists of three tarsomeres. Presumably, the last common ancestor of the Dermaptera possessed an arolium, since this structure occurs in the most basal taxa: Diplatyidae, Karschiellidae (partim, adults), Pygidicranidae partim, and Apachyidae. The absence of arolium in two of the pygidicranid taxa is probably due to a secondary loss. The arolium seems to be reduced in the 'higher Dermaptera' and amongst them, only the Geracinae, which belong to the Spongiphoridae and, hence, to the well supported Eudermaptera [European Journal of Entomology, 98 (2001), 445], evolved this structure convergently. The character state distribution for euplantulae suggests their evolution being similar to that of the arolium. All species of Tagalina possess a specialised tarsus with a strongly dilated second tarsomere. The same applies to the Forficulidae. However, their relatively remote phylogenetic position to Tagalina burri is a convincing reason to assume convergent evolution of this character. The Chelisochidae, with a slender, elongated second tarsomere, possess a unique structure, which supports their monophyly. The special, heart shaped structure of the second tarsal segments in the Forficulidae suggests their monophyly. The attachment structures of Hemimerus vosseleri are highly derived and probably autapomorphic for this taxon.     

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.     

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.     

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.     

Two functional types of attachment pads on a single foot in the Namibia bush cricket Acanthoproctus diadematus (Orthoptera: Tettigoniidae)

Insects have developed different structures to adhere to surfaces. Most common are smooth and hairy attachment pads, while nubby pads have also been described for representatives of Mantophasmatodea, Phasmida and Plecoptera. Here we report on the unusual combination of nubby and smooth tarsal attachment structures in the !nara cricket Acanthoproctus diadematus. Their three proximal tarsal pads (euplantulae) have a nubby surface, whereas the most distal euplantula is rather smooth with a hexagonal ground pattern resembling that described for the great green bush-cricket Tettigonia viridissima. This is, to our knowledge, the first report on nubby euplantulae in Orthoptera and the co-occurrence of nubby and smooth euplantulae on a single tarsus in a polyneopteran species. When adhering upside down to a horizontal glass plate, A. diadematus attaches its nubby euplantulae less often, compared to situations in which the animal is hanging upright or head down on a vertical plate. We discuss possible reasons for this kind of clinging behaviour, such as morphological constrains, the different role of normal and shear forces in attachment enhancement of the nubby and smooth pads, ease of the detachment process, and adaptations to walking on cylindrical substrates.     

Dandelion diaspore dispersal: frictional anisotropy of cypselae of Taraxacum officinale enhances their interlocking with the soil

Plant and Soil - Green roofs are important novel urban ecosystems, but their shallow substrates can create plant water deficits in dry climates. Physiological approaches can improve green roof...     

Biological control of microbial attachment: a promising alternative for mitigating membrane biofouling

Microbial attachment to a solid surface is a universal phenomenon occurring in both natural and engineering systems and is responsible for various types of biofouling. Membrane systems have been widely applied in drinking water production, wastewater reuse, and seawater desalination. However, membrane biofouling is the bottleneck that limits the development of membrane systems. In this review, some biological control strategies of microbial attachment which would have great potential in alleviating membrane biofouling are discussed, including inhibition of quorum sensing system, nitric oxide-induced biofilm dispersal, enzymatic disruption of extracellular polysaccharides, proteins, and DNA, inhibition of microbial attachment by energy uncoupling, use of cell wall hydrolases, and disruption of biofilm by bacteriophage. It appears that biological control of microbial attachment would be a novel and promising alternative for mitigating membrane biofouling and would be a new research niche that deserves further study.     

Contact behaviour of tenent setae in attachment pads of the blowfly Calliphora vicina (Diptera, Calliphoridae)

To enable strong attachment forces between pad and substrata, a high proximity between contacting surfaces is required. One of the mechanisms, which can provide an intimate contact of solids, is a high flexibility of both materials. It has been previously presumed that setae of hairy attachment pads of insects are composed of flexible cuticle, and are able to replicate the surface profile. The aim of this work was to visualise the contact behaviour of the setae by freezing-substitution technique to understand setal mechanics while adhering to a smooth surface. This approach revealed considerable differences in the area of the setal tips between contacting and non-contacting pulvilli. Based on the assumption that setae behave like a spring pushed by the tip, a spring constant of 1.31 N m(-1) was calculated from direct measurements of single setae by atomic force microscopy. In order to explain the relationship between the behaviour of the attachment setae at a microscale and leg movements, high-speed video recordings were made of walking flies. This data show that some proximal movement of the leg is present during contact formation with the substrate.     

C-terminus of a long alpha-neurotoxin is highly mobile when bound to the nicotinic acetylcholine receptor: a time-resolved fluorescence anisotropy approach

To better understand how alpha-neurotoxins interact with the acetylcholine receptor, four fluorescein isothiocyanate derivatives of the siamemsis alpha-cobratoxin were prepared (conjugated to the epsilon-amino group in Lys(23), Lys(35), Lys(49), or Lys(69)) and the time-resolved fluorescence anisotropy of each conjugate was measured free in solution and bound to the Torpedo acetylcholine receptor. All the conjugated reporter groups displayed a high and comparable level of mobility free in solution. When receptor bound, on the other hand, significant differences in the conformational dynamics of the reporter groups were observed with the C-terminal Lys(69) derivative displaying by far the greatest mobility strongly suggesting that the C-terminal domain of the bound neurotoxin is highly mobile and does not participate in the toxin-nAChR binding surface. Additionally, this study demonstrates the utility of time-resolved fluorescence anisotropy to characterize the interaction of heteroproteins.     

Modularity in attachment organs of African Cichlidogyrus (Platyhelminthes: Monogenea: Ancyrocephalidae) reflects phylogeny rather than host specificity or geographic distribution

Cichlidogyrus spp. (Monogenea, Ancyrocephalidae) are common parasites of cichlid fishes from Africa and the Levant. They display important morphological variation in their attachment apparatus and infect a broad host spectrum throughout a wide geographic range. Thus, they offer an interesting model to investigate to what extent the phenotypic variability of the attachment organ among congeners is related to host specificity, geographic/environmental components, or phylogeny. A geometric morphometric approach was carried out to analyse the shape variation of sclerotized structures of the attachment organ within 66 African species of the genus Cichlidogyrus. The interspecific shape comparison supports the presence of three main morphological configurations, each consisting of a given combination of particular sclerite shapes. Moreover, data emphasize strong coordination and integration (shape co‐variation) among the different sclerites jointly forming the attachment organ. Although attachment apparatuses are usually considered to be the result of adaptive processes and must be adapted to the hosts and local environmental conditions, we found no relationship between these clusters and host specificity or geographical distribution. Nevertheless, groups are partially congruent with those obtained with the molecular phylogeny of a subset of species, suggesting a phylogenetic constraint rather than an adaptation to either hosts or environment. Because of the necessity to form a functional entity, modularity within attachment organ imposes important evolutionary constraint. This provides new insights into the evolvability of attachment organs, as well as into the morphological basis of host specificity and host–parasite co‐evolutionary interaction in helminth parasites. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 694–706.     

Mechanical stresses in abdominal aortic aneurysms: influence of diameter, asymmetry, and material anisotropy

Biomechanical studies suggest that one determinant of abdominal aortic aneurysm (AAA) rupture is related to the stress in the wall. In this regard, a reliable and accurate stress analysis of an in vivo AAA requires a suitable 3D constitutive model. To date, stress analysis conducted on AAA is mainly driven by isotropic tissue models. However, recent biaxial tensile tests performed on AAA tissue samples demonstrate the anisotropic nature of this tissue. The purpose of this work is to study the influence of geometry and material anisotropy on the magnitude and distribution of the peak wall stress in AAAs. Three-dimensional computer models of symmetric and asymmetric AAAs were generated in which the maximum diameter and length of the aneurysm were individually controlled. A five parameter exponential type structural strain-energy function was used to model the anisotropic behavior of the AAA tissue. The anisotropy is determined by the orientation of the collagen fibers (one parameter of the model). The results suggest that shorter aneurysms are more critical when asymmetries are present. They show a strong influence of the material anisotropy on the magnitude and distribution of the peak stress. Results confirm that the relative aneurysm length and the degree of aneurysmal asymmetry should be considered in a rupture risk decision criterion for AAAs.     

Anatomy and ultrastructure of epidermal cells in the haustorium of a parasitic flowering plant,Cuscuta japonica, during attachment to the host

Changes of epidermal cells in the haustorium of the parasiticCuscuta japonica during its attachment to the host plantimpatiens balsamina were studied with light and electron microscopy. In the transverse sections of dodder stems not in contact with the host, epidermal cells had rounded outlines. However, when haustorial initials developed in the cortex of the parasite stem at the contact site, the epidermal cells had more dense cytoplasm and conspicuous nuclei than before, and their outline was flat in the longitudinal section. As meristem cells developed from those initials, the epidermal cells became more elongated. When the haustorium was fully matured, the apical tips of the elongated epidermal cells at the contact site branched like toes, producing numerous projections via cell wall invaginations. This event caused spaces to form between the projections; coincidently, the surface area of the apical ends of the epidermal cells increased. The dense cytoplasm at those projections contained prominent nuclei and abundant other organelles, suggesting a active metabolism. Osmiophilic particles, releasing into the cell walls from the cytoplasm, were though to be associated with the loosening and elongating of the epidermal cell walls. Dense and homogeneous materials were secreted within the spaces between the projections. These materials could play an important role in cementing the haustorium onto the surface of the host organ.     

Hydrophobic forces are responsible for the folding of a highly potent natriuretic peptide analogue at a membrane mimetic surface: An NMR study

A conformational study by nmr spectroscopy was performed with the highly active 28-residue hybrid natriuretic peptide analogue pBNP1 [M. Mimeault, A. De Léan, M. Lafleur, D. Bonenfant, and A. Fournier (1995) Biochemistry, Vol. 34, pp. 955–964], which consists of the cyclic peptide core of pBNP32 and the N- and C-terminal exocyclic segments of rANP(99–126). In purely aqueous solution pBNP1 exhibits random coil behavior as evidenced by the almost complete absence of structurally significant nmr observables. By contrast, elements of secondary structure emerged upon the addition of dodecylphosphocholine micelles to the aqueous sample. Nuclear Overhauser effect distance-restrained molecular dynamics simulations in conjunction with torsional angle determinations permitted the generation of a reasonable model of the lipid-bound conformation of pBNP1. According to this model, pBNP1 adopts turn-like features in the cyclic and C-terminal regions of the peptide, but remains quite flexible in the N-terminal segment. Two hydrophobic cores separated by a hydrophilic cleft were also evident in the generated structure. A mechanism is proposed whereby the hydrophobic interactions necessary to stabilize a folded structure of pBNP1 are facilitated by the presence of the membrane-like polar/apolar interface provided by the phospholipid micelles. © 1997 John Wiley & Sons, Biopoly 42: 37–48, 1997     

Expression of a highly toxic protein, Bax, in Escherichia coli by attachment of a leader peptide derived from the GroES cochaperone

Expression of the human apoptosis modulator protein Bax in Escherichia coli is highly toxic, resulting in cell lysis at very low concentrations (Asoh, S., et al., J. Biol. Chem. 273, 11384-11391, 1998). Attempts to express a truncated form of murine Bax in the periplasm by using an expression vector that attached the OmpA signal sequence to the protein failed to alleviate this toxicity. In contrast, attachment of a peptide based on a portion of the E. coli cochaperone GroES reduced Bax's toxicity significantly and allowed good expression. The peptide, which was attached to the N-terminus, included the amino acid sequence of the mobile loop of GroES that has been demonstrated to interact with the chaperonin, GroEL. Under normal growth conditions, expression of this construct was still toxic, but generated a small amount of detectable recombinant Bax. However, when cells were grown in the presence of 2% ethanol, which stimulated overproduction of the molecular chaperones GroEL and DnaK, toxicity was reduced and good overexpression occurred. Two-dimensional gel electrophoresis analysis showed that approximately 15-fold more GroES-loop-Bax was produced under these conditions than under standard conditions and that GroEL and DnaK were elevated approximately 3-fold.