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Insect cuticle can reach a wide range of material properties, which is thought to be the result of adaptations to applied mechanical stresses. Biomechanical mechanisms behind these property variations remain largely unknown. To fill this gap, here we performed a comprehensive study by simultaneous investigation of the microstructure, sclerotization and the elasticity modulus of the specialized cuticle of the femora of desert locusts. We hypothesized that, considering their different roles in jumping, the femora of fore-, mid- and hind legs should be equipped with cuticles that have different mechanical properties. Surprisingly, our results showed that the hind femur, which typically bears higher stresses, has a lower elasticity modulus than the fore and mid femora in the longitudinal direction. This is likely due to the lower sclerotization and different microstructure of the hind femur cuticle. This allows for some deformability in the femur wall and is likely to reduce the risk of mechanical failure. In contrast to both other femora, the hind femur is also equipped with a set of sclerotized ridges that are likely to provide it with the required stiffness to withstand the mechanical loads during walking and jumping. This paper is one of only a few comprehensive studies on insect cuticle, which advances the current understanding of the relationship between the structure, material property and function in this complex biological composite. Insect cuticle is a biological composite with strong anisotropy and wide ranges of material properties. Using an example of the femoral cuticle of desert locusts, we measured the elasticity modulus, microstructure and sclerotization level of the cuticle. Our results show that, although the hind femur withstands most of the stress during locomotion, it has a lower elasticity modulus than the fore and mid femora. This is likely to be a functional adaption to jumping, in order to allow small deformations of the femur wall and reduce the risk of material failure. Our results deepen the current understanding of the structure-material-function relationship in the complex insect cuticle. [Display omitted] [ABSTRACT FROM AUTHOR]

Insects thrived soon after they acquired the ability to fly. Beyond the reach of the non-flying competitors, flying insects colonized a wide variety of habitats. Although flight is an efficient way to disperse and escape predators, it is energetically costly. Hence, various strategies are served to enhance flight efficiency as much as possible. A striking example is the development of wing-to-wing coupling mechanisms in many neopterous insects to minimize the aerodynamic interference of fore and hind wings. However, it remains unclear how the seemingly delicate coupling mechanisms can withstand excessive mechanical stresses encountered during flight. Here we studied the complicated coupling mechanism of drone honey bees, which consists of a set of tiny hooks and a thickened membrane. We found that the durability of the coupling mechanism results from two complementary strategies. First, the angles at which hooks and membrane are coupled and uncoupled may be adjusted, so that the resulting stresses are minimized. Second, the out-of-plane structure, soft base and pronounced tip reduce the stress developed in the hooks, yet maintaining the coupling strength. We anticipate our study, which presents the first numerical model of insect wing coupling mechanisms, to be a starting point for the development of more sophisticated models in the future. Such models are particularly useful for comparative analysis of the influence of different morphological features on the functionality of complex coupling mechanisms. Hamuli, or 'tiny hooks', is the Greek term for hook-like structures on the anterior margin of honey bee hind wings. By fitting into the fold posterior margin of fore wings, the hooks couple the two wings to each other. Despite their seemingly fragile structure, the hooks withstand substantial mechanical stresses. We show that the out-of-plane structure, soft base and pronounced tip are morphological features that enhance the durability of the hooks, without compromising their function. Image, graphical abstract [ABSTRACT FROM AUTHOR]

A striking characteristic of insect cuticle is the wide range of its material property values, with respect to stiffness, strength and toughness. The elastic modulus of cuticle, for instance, ranges over seven orders of magnitude in different structures and different species. Previous studies suggested that this characteristic is influenced by the microstructure and sclerotization of cuticle. However, the relative role of the two factors in determining the material properties of cuticle is unknown. Here we used a combination of scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and nanoindentation, to investigate the effect of microstructure and sclerotization on the elastic modulus of tibiae of desert locusts. Our results showed that tibial cuticle is an anisotropic material with the highest elastic modulus along the tibial axis. This is likely because majority of the fibers in the cuticle are oriented along this axis. We also found that the hind tibia has a significantly higher elastic modulus, compared with the fore and mid tibiae. This is likely due to the higher sclerotization level of the hind tibia cuticle, and seems to be an adaptation to the locust locomotion by jumping, in which axial loads in the hind tibiae may reach several times the insect body weight. Our results suggest that while sclerotization determines the difference between the elastic moduli of the tibiae, anisotropic properties of each tibia is controlled by the specific fiber orientation. Our study provides one of only a few comprehensive investigations on insect cuticle, and helps to better understand the structure-material-function relationship in this complex biological composite. Insect cuticle is a biological composite with strong anisotropy and wide ranges of material properties. Using an example of the tibial cuticle of desert locusts, we examined the role of two influential factors on the elastic modulus of cuticle: microstructure and sclerotization. Our results suggested the strong influence of sclerotization on the variation of the elastic modulus among fore, mid and hind tibiae, and that of the microstructure on the anisotropy of each tibia. Our results deepens the current understanding of the structure-material-function relationship in complex insect cuticle. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Stink bugs have wing coupling mechanisms to synchronize flapping of their wings. The wing coupling is performed through a clamp-like structure on the fore wing (i.e. hemelytron) and a rolled margin on the hind wing. Here we used modern imaging techniques to investigate structural characteristics and material composition of the wing coupling of the stink bug Nezara viridula. We found that the surfaces of the clamp-like structure and the rolled margin are covered by highly-sclerotized microtrichia, which are expected to reduce friction between the wings during flapping flight. Micro-force measurements showed that fore and hind wings can be coupled only in certain angles ranging from 40.6° to 267.7° The results further showed that the force required to uncouple fore and hind wings is maximal for a range of angles which they make with each other during flight (127.1°–238.9°). In contrast to previous observations on some other insect species, the removal of the wing coupling in stink bugs led to complete loss of flight ability. In summary, we concluded that the shape, material composition and orientation of the coupling structure guarantee a robust fore wing to hind wing coupling during flight and a fast, easy uncoupling at rest. Although the coupling mechanism of insect fore wing and hind wing has long been described, the functionality of this mechanism still remains largely unknown. In the present work, using a combination of modern imaging techniques and mechanical testing, we studied the functional morphology of the fore wing-hind wing coupling mechanism of the stink bug Nezara viridula. Our study reveals the crucial role of the mechanism in the flight ability of the stink bug and sheds light on the structure-property-function relationships of the functional diptery in insects. Image, graphical abstract [ABSTRACT FROM AUTHOR]

This study models convective transport of soluble surfactant in a foam fractionation system with reflux. Owing to reflux, initial surfactant concentration in films is lower than in Plateau borders. Marangoni flows and film drainage flows arise convecting surfactant both on the film surface and in the bulk. An interface is set up within the film bulk called a separatrix: this divides two regions of uniform surfactant concentration, one with concentration equal to that of the initial film and one with concentration equal to that in the Plateau border. The evolution of the separatrix is tracked to determine surfactant recovery and enrichment for the film. Surfactant lean films benefit most from reflux. However for films that are initially comparatively surfactant rich, recovery might actually decrease at long times owing to film drainage. Nonetheless surfactant lean films and those containing surfactant with only moderate solubility benefit from reflux even despite film drainage. • Foam fractionation with reflux is modelled for a convected soluble surfactant. • Convection occurs on film surface and within bulk of foam films. • Separatrix divides material in bulk from newly arrived material from Plateau border. • Solutions that are leaner in surfactant benefit from reflux. • Foam drainage can cause surfactant recovery to decrease at longer times. [ABSTRACT FROM AUTHOR]

Ctenoid scales protect the fish body against predators and other environmental impacts. At the same time, they allow for sufficient degree of flexibility to perform species-specific locomotion. The scales of the flatfish Solea solea were chosen to study the specific mechanical behavior and material properties of the ctenoid scales. Using scanning electron microscopy and micro-computed tomography, three-dimensional asymmetric structures of the stacked mineralized ctenial spines in the posterior field, which is a part of the scales exposed to the environment, were examined in detail. Nanoindentations on the surface of the ctenial spines indicated that the elastic modulus and hardness of these mineralized structures are about 14 GPa and 0.4 GPa, respectively. The spines appeared to be connected to each other by means of joint-like structures containing soft tissues. Bending tests showed that the ctenoid scales have two functional zones: a stiff supporting main body and an anisotropically deformable posterior field. While the stiff plate-like main body provides support for the whole scale, the deformable joint-like structures in the ctenial spines increase the deformability of the posterior field in downward bending. During upward bending, however, the spines prevent complete folding of the posterior field by an interlocking effect. In contrast to the continuously mineralized cycloid scales, ctenoid scales combine two conflicting properties: They are hard to protect the body of fish against predators and other environmental impacts, yet flexible enough to allow for sufficient degree of body bendability for locomotion. To understand the structural background underlying this specific biomechanical feature, here we investigated the scales of the flatfish Solea solea. For the first time, we demonstrated the presence of joint-like structures within the scales, which increase scale deformability during downward bending, but prevent scale deformation during upward bending by interlocking. Our results shed lights on the material-structure-function relationships in ctenoid scales, as well as on their functional adaptations to the specific environment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Foam fractionation with reflux is modelled for a soluble surfactant. • Reflux induces Marangoni-driven surfactant transfer from Plateau border to film. • Two isotherms (global and local Henry) relate surfactant on and within foam film. • Surfactant transfer slowed by solubility and by local Henry isotherm. • Film drainage reduces surfactant recovery but improves enrichment. This study models soluble surfactant transport on and within a foam film during a foam fractionation process. Marangoni flow drives surfactant onto the film, and also surfactant concentration is assumed to be uniform across the thin foam film. Adsorption isotherms are used to couple mass transfer equations, so as to determine the evolution of the total amount of surfactant (surface plus bulk) at any film location. Surfactant transport is considered both in the absence and presence of film drainage. It is observed that having soluble surfactant slows down evolution of Marangoni-driven flow compared to cases assuming insoluble surfactant. This is because in soluble surfactant cases, surfactants diffuse to the bulk even whilst being transferred by Marangoni flow onto the film surface. Furthermore, it is observed that a quasisteady state typically occurs after a long time, such that Marangoni flow and film drainage flow become comparable. [ABSTRACT FROM AUTHOR]

[Display omitted] • Inspired by vein-joints of insect wings, we developed adaptive structures that change shape and stiffness upon loading. • We studied key design parameters of bioinspired structures, establishing a relation between their displacements and design. • The use of purely structural strategies facilitates the implementation, scalability, and adjustability of our designs. • In practice, our designs showed effectiveness and potential for creating properties such as asymmetry and heterogeneity. • Our results allow a better understanding of the importance of morphological diversity for the biomechanics of insect wings. Modern engineering requires structural components that adapt to continuously changing conditions. Adaptability leads to multi-functionality, enhanced durability, and functional efficiency of mechanical systems. That is why adaptive structures have received increasing attention, especially in robotics, aerospace, automotive, and biomedical engineering. Current adaptive structures require significant active actuations and controls, factors that add to their complexity, weight, and production costs. In contrast, most biological adaptive systems respond to external stimuli in a passive-automatic way. Here, inspired by a striking biological example, i.e. insect wings and specifically their vein-joints, we develop structures in which adaptability is determined by the presence of a network of bioinspired compliant joints. By systematically changing the key geometric parameters of the bioinspired joints, we show that they can be designed in a variety of patterns to passively control the adaptability of the structures under loading. We further test the performance of the bioinspired joints in practice. The simplicity, scalability, and adjustability are the features that facilitate the widespread community uptake of our designs. [ABSTRACT FROM AUTHOR]

• Honeybee coupling structure is made up of a strong sclerotized cuticle. • The coupling structure allows a large wing angle range during flight. • The coupled wing is positively cambered during the upstroke and downstroke. • The wing angle range augments lift and drag with a higher rate of drag augment. Worker honeybees (Apis mellifera) are morphologically four-winged, but are functionally dipterous insects. During flight, their fore- and hindwings are coupled by means of the forewing posterior rolled margin (PRM) and hindwing hamuli. Morphological analysis shows that the PRM can be connected to the hamuli, so that the fore- and hindwing are firmly hinged, and can rotate with respect to each other. In the present study, using a combination of scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM), we investigate the micromorphology and material composition of the coupling structures on both fore- and hindwings. High-speed filming is utilized to determine the angle variation between the fore- and hindwings in tethered flight. Using sets of two-dimensional (2D) computation fluid dynamic analyses, we further aim to understand the influence of the angle variation on the aerodynamic performance of the coupled wings. The results of the morphological investigations show that both PRM and hamuli are made up of a strongly sclerotized cuticle. The sclerotized hinge-like connection of the coupling structure allows a large angle variation between the wings (135°–235°), so that a change is made from an obtuse angle during the pronation and downstroke to a reflex angle during the supination and upstroke. Our computational results show that in comparison to a model with a rigid coupling hinge, the angle variation of a model having a flexible hinge results in both increased lift and drag with a higher rate of drag increase. This study deepens our understanding of the wing-coupling mechanism and functioning of coupled insect wings. [ABSTRACT FROM AUTHOR]

Durability and load-bearing are difficult to be combined in engineering systems. Hence, in majority of man-made structures, the two characteristics are typically mutually exclusive. Nature, however, has provided us with design strategies, through which many biological systems have overcome this conflict. Insect wings represent a striking example of such a combination. A key to this lies in the presence of vein joints. Here we 3D printed bio-inspired joints, akin to those of insect wings and tested their mechanical performance under both static and cyclic loadings. We used the so-called 'flexible joints', which had a high durability, and engineered them to further enhance their load-bearing capacity. We then implemented them into the design of the first 3D printed bio-inspired kite. The manufactured kite showed a stable flight and withstood loads induced by strong wind gusts without failure. The concept developed here can be applied to other engineering designs that pursue a compromise between load-bearing and durability. At the end, we used our data to better understand the complexities of insect wings with respect to their local and global deformations and fracture resistance. Unlabelled Image • We developed a bio-inspired design strategy to combine two mutually exclusive characteristics of loading-bearing and durability. • Our design strategy is purely structural and, therefore, can be easily modified and implemented in engineering systems. • Using the developed strategy, we designed and fabricated the first bio-inspired 3D printed kite that can withstand strong wind gusts. • The example of the kite confirmed the efficiency of our bio-inspired strategy in practice. • A similar design principle could be used to develop load-bearing, yet durable, engineering structures. [ABSTRACT FROM AUTHOR]

A great deal of computational power and time is necessary for the simulation of highly heterogeneous fractured reservoirs with complicated geometry. Simulating such largescale complex reservoirs with both minimum time and maximum accuracy has consistently remained a topic of concern to reservoir simulation engineers worldwide. The currently used linear solvers in well-known commercial simulators that utilize classical methods such as Nested Factorization (NF) and Incomplete LU Factorization (ILU) as their preconditioners, all suffer from severe convergence problems in models with high heterogeneity and/or large number of non-neighbor connections. To overcome such problems, a novel Adaptive Algebraic Multi-grid algorithm (AAMG) is proposed to be used in a constrained pressure residual (CPR) preconditioner, abbreviated as CPR-AAMG, in order to solve the governing discretized three-dimensional partial differential equations. The implemented CPR preconditioner which uses AAMG as the preconditioner for the elliptic pressure equation, and the Blocked ILU for the hyperbolic saturation equations, is a robust way for damping both smooth pressure field and high frequency saturation field errors in giant reservoir models. The findings of the current study illustrate that the developed Biconjugate Gradient Stabilized (BiCG-Stab) solver preconditioned by CPR-AAMG is capable of achieving acceptable results of high efficiency and robustness in the SPE10 project which is renowned as an enormous challenge for linear solvers due to the highly heterogeneous porosity and permeability values. The novelty of the proposed CPR-AAMG preconditioner is its ability to solve three-dimensional black oil models of giant, complex and heterogeneous fractured reservoirs without any convergence problems with reduction in time and required computational power. • Developing a novel adaptive CPR-AMG (named CPR-AAMG) preconditioner with BiCG-Stab as the linear solver. • Demonstrating the developed preconditioner in SPE10 model, an enormous challenge for solvers due to its heterogeneity. • Comparing the simulation runtime with other well-known preconditioners. • Validating the accuracy of the developed preconditioner. [ABSTRACT FROM AUTHOR]