nils-herrmann/clean_scirepeval huggingface dataset:
A lightweight, biological structure with tailored stiffness: The feather vane.
Venue: Acta Biomaterialia

The flying feathers of birds are keratinous appendages designed for maximum performance with a minimum weight penalty. Thus, their design contains ingenious combinations of components that optimize lift, stiffness, aerodynamics, and damage resistance. This design involves two main parts: a central shaft that prescribes stiffness and lateral vanes which allows for the capture of air. Within the feather vane, barbs branch from the shaft and barbules branch from barbs, forming a flat surface which ensures lift. Microhooks at the end of barbules hold barbs tightly together, providing the close-knit, unified structure of the feather vane and enabling a repair of the structure through the reattachment of un-hooked junctions. Both the shaft and barbs are lightweight biological structures constructed of keratin using the common motif of a solid shell and cellular interior. The cellular core increases the resistance to buckling with little added weight. Here we analyze the detailed structure of the feather barb and, for the first time, explain its flexural stiffness in terms of the mechanics of asymmetric foam-filled beams subjected to bending. The results are correlated and validated with finite element modeling. We compare the flexure of single barbs as well as arrays of barbs and find that the interlocking adherence of barbs to one another enables a more robust structure due to minimized barb rotation during deflection. Thus, the flexure behavior of the feather vane can be tailored by the adhesive hooking between barbs, creating a system that mitigates damage. A simplified three-dimensional physical model for this interlocking mechanism is constructed by additive manufacturing. The exceptional architecture of the feather vane will motivate the design of bioinspired structures with tailored and unique properties ranging from adhesives to aerospace materials.



Despite its importance to bird flight, literature characterizing the feather vane is extremely limited. The feather vane is composed of barbs that branch from the main shaft (rachis) and barbules that branch from barbs. In this study, the flexural behavior of the feather barb and the role of barbule connections in reinforcing the feather vane are quantitatively investigated for the first time, both experimentally and theoretically. Through the performed experiments, structure-function relationships within the feather vane are uncovered. Additionally, in the proposed model the sophisticated structure of the barbs and the interlocking mechanism of the feather vane are simplified to understand these processes in order to engineer new lightweight structures and adhesives.
Fatty Acids Identified in the Burmese Python Promote Beneficial Cardiac Growth
Venue: Science

A specific set of circulating fatty acids triggers cardiac hypertrophy in snakes and mammals. Burmese pythons display a marked increase in heart mass after a large meal. We investigated the molecular mechanisms of this physiological heart growth with the goal of applying this knowledge to the mammalian heart. We found that heart growth in pythons is characterized by myocyte hypertrophy in the absence of cell proliferation and by activation of physiological signal transduction pathways. Despite high levels of circulating lipids, the postprandial python heart does not accumulate triglycerides or fatty acids. Instead, there is robust activation of pathways of fatty acid transport and oxidation combined with increased expression and activity of superoxide dismutase, a cardioprotective enzyme. We also identified a combination of fatty acids in python plasma that promotes physiological heart growth when injected into either pythons or mice.
Dynamic fracture resilience of elk antler: Biomimetic inspiration for improved crashworthiness
Venue: JOM

The antler of the North American elk has been shown to have impressive fracture resistance under quasi-static loads, but given its viscoelastic behavior and impact nature of loading, questions remain as to its mechanical, and in particular, fracture behavior under dynamic loading. Samples were tested using a unique split-pressure Hopkin-son bar (SPHB) for four-point bending experiments in order to measure the fracture toughness of this material Interestingly, the hierarchical structure of antler had a strong influence on crack propagation characteristics, and cracks tended to propagate along the osteonal growth direction, whether loaded parallel or perpendicular to the osteonal growth direction. This occurred to such a degree so as to stop all crack propagation through the sample on transverse specimens, thus inhibiting the ability to measure a valid crack initiation toughness and demonstrating the extreme resilience of antler to resist dynamic fracture. The high resilience of antler to impact loading may serve as biomimetic inspiration to future material development for crashworthiness and defense applications.
Lymphatic vascular morphogenesis in development, physiology, and disease
Venue: Journal of Cell Biology

The lymphatic vasculature constitutes a highly specialized part of the vascular system that is essential for the maintenance of interstitial fluid balance, uptake of dietary fat, and immune response. Recently, there has been an increased awareness of the importance of lymphatic vessels in many common pathological conditions, such as tumor cell dissemination and chronic inflammation. Studies of embryonic development and genetically engineered animal models coupled with the discovery of mutations underlying human lymphedema syndromes have contributed to our understanding of mechanisms regulating normal and pathological lymphatic morphogenesis. It is now crucial to use this knowledge for the development of novel therapies for human diseases.
Infrared receptors in pyrophilous (“fire loving”) insects as model for new un-cooled infrared sensors
Venue: Beilstein Journal of Nanotechnology

Beetles of the genus Melanophila and certain flat bugs of the genus Aradus actually approach forest fires. For the detection of fires and of hot surfaces the pyrophilous species of both genera have developed infrared (IR) receptors, which have developed from common hair mechanoreceptors. Thus, this type of insect IR receptor has been termed photomechanic and shows the following two special features: (i) The formation of a complex cuticular sphere consisting of an outer exocuticular shell as well as of a cavernous microfluidic core and (ii) the enclosure of the dendritic tip of the mechanosensitive neuron inside the core in a liquid-filled chamber. Most probably a photomechanic IR sensillum acts as a microfluidic converter of infrared radiation which leads to an increase in internal pressure inside the sphere, which is measured by a mechanosensitive neuron. A simple model for this biological IR sensor is a modified Golay sensor in which the gas has been replaced by a liquid. Here, the absorbed IR radiation results in a pressure increase of the liquid and the deflection of a thin membrane. For the evaluation of this model analytical formulas are presented, which permits the calculation of the pressure increase in the cavity, the deformation of the membrane and the time constant of an artificial leak to compensate ambient temperature changes. Some organic liquids with high thermal expansion coefficients may improve the deflection of the membrane compared to water.
Ice Nucleation Activity in Lichens
Venue: Applied and Environmental Microbiology

A newly discovered form of biological ice nucleus associated with lichens is described. Ice nucleation spectra of a variety of lichens from the southwestern United States were measured by the drop-freezing method. Several epilithic lichen samples of the genera Rhizoplaca, Xanthoparmelia, and Xanthoria had nuclei active at temperatures as warm as −2.3°C and had densities of 2.3 × 106 to more than 1 × 108 nuclei g−1 at −5°C (2 to 4 orders of magnitude higher than any plants infected with ice nucleation-active bacteria). Most lichens tested had nucleation activity above −8°C. Lichen substrates (rocks, plants, and soil) showed negligible activity above −8°C. Ice nucleation-active bacteria were not isolated from the lichens, and activity was not destroyed by heat (70°C) or sonication, indicating that lichen-associated ice nuclei are nonbacterial in origin and differ chemically from previously described biological ice nuclei. An axenic culture of the lichen fungus Rhizoplaca chrysoleuca showed detectable ice nucleation activity at −1.9°C and an ice nucleation density of 4.5 × 106 nuclei g−1 at −5°C. It is hypothesized that these lichens, which are both frost tolerant and dependent on atmospheric moisture, derive benefit in the form of increased moisture deposition as a result of ice nucleation.
Cold-adapted tubulins in the glacier ice worm, Mesenchytraeus solifugus.
Venue: Gene

Glacier ice worms, Mesenchytraeus solifugus and related species, are the only known annelids that survive obligately in glacier ice and snow. One fundamental component of cold temperature adaptation is the ability to polymerize tubulin, which typically depolymerizes at low physiological temperatures (e.g., <10 degrees C) in most temperate species. In this study, we isolated two alpha-tubulin (Msalpha1, Msalpha2) and two beta-tubulin (Msbeta1, Msbeta2) subunits from an ice worm cDNA library, and compared their predicted amino acid sequences with homologues from other cold-adapted organisms (e.g., Antarctic fish, ciliate) in an effort to identify species-specific amino acid substitutions that contribute to cold temperature-dependent tubulin polymerization. Our comparisons and predicted protein structures suggest that ice worm-specific amino acid substitutions stabilize lateral contact associations, particularly between beta-tubulin protofilaments, but these substitutions occur at different positions in comparison with other cold-adapted tubulins. The ice worm tubulin gene family appears relatively small, comprising one primary alpha- and one primary beta-tubulin monomers, though minor isoforms and pseudogenes were identified. Our analyses suggest that variation occurs in the strategies (i.e., species-specific amino acid substitutions, gene number) by which cold-adapted taxa have evolved the ability to polymerize tubulin at low physiological temperatures.
Loss of top-down biotic interactions changes the relative benefits for obligate mutualists
Venue: Proceedings of The Royal Society B: Biological Sciences

The collapse of mutualisms owing to anthropogenic changes is contributing to losses of biodiversity. Top predators can regulate biotic interactions between species at lower trophic levels and may contribute to the stability of such mutualisms, but they are particularly likely to be lost after disturbance of communities. We focused on the mutualism between the fig tree Ficus microcarpa and its host-specific pollinator fig wasp and compared the benefits accrued by the mutualists in natural and translocated areas of distribution. Parasitoids of the pollinator were rare or absent outside the natural range of the mutualists, where the relative benefits the mutualists gained from their interaction were changed significantly away from the plant's natural range owing to reduced seed production rather than increased numbers of pollinator offspring. Furthermore, in the absence of the negative effects of its parasitoids, we detected an oviposition range expansion by the pollinator, with the use of a wider range of ovules that could otherwise have generated seeds. Loss of top-down control has therefore resulted in a change in the balance of reciprocal benefits that underpins this obligate mutualism, emphasizing the value of maintaining food web complexity in the Anthropocene.
Nesting biology of the mangrove mud-nesting ant Polyrhachis sokolova Forel (Hymenoptera, Formicidae) in northern Australia
Venue: Insectes Sociaux

The nest sites of the mud-nesting ant Polyrhachis sokolova were studied in Darwin Harbour mangroves. They were found from the Ceriops tagal zone to the Rhizophora stylosa zone at elevations ranging from 7.22 to 5.99 meters above the lowest astronomical tide (LAT), which means that the nests were inundated in 13‐61% of all high tides and for durations of up to 3.5 hours. The nest structure was studied by excavating nests and making a cast of the galleries using polyurethane foam. The nests were quite extensive, normally with two elevated nest entrances and galleries down to depths of 45 cm. The loose soil particles at the nest entrances collapsed when the tide reached them and formed a stopper which prevented water from intruding into the nest. In this way, the galleries remained dry during high tide. The ants showed a clear swimming or "walking on the surface" behaviour when they returned to the nest just before the entrance collapsed and during ebb. The tolerance of the ants to submergence was tested in the laboratory, with 50% mortality after 11 hours submergence in seawater at 23 °C, and only 3.5 hours in water at 33 °C. Therefore, the nesting behaviour with trapped air in the galleries is necessary for survival in these environments.
Capillarity-based switchable adhesion
Venue: Proceedings of the National Academy of Sciences of the United States of America

Drawing inspiration from the adhesion abilities of a leaf beetle found in nature, we have engineered a switchable adhesion device. The device combines two concepts: The surface tension force from a large number of small liquid bridges can be significant (capillarity-based adhesion) and these contacts can be quickly made or broken with electronic control (switchable). The device grabs or releases a substrate in a fraction of a second via a low-voltage pulse that drives electroosmotic flow. Energy consumption is minimal because both the grabbed and released states are stable equilibria that persist with no energy added to the system. Notably, the device maintains the integrity of an array of hundreds to thousands of distinct interfaces during active reconfiguration from droplets to bridges and back, despite the natural tendency of the liquid toward coalescence. We demonstrate the scaling of adhesion strength with the inverse of liquid contact size. This suggests that strengths approaching those of permanent bonding adhesives are possible as feature size is scaled down. In addition, controllability is fast and efficient because the attachment time and required voltage also scale down favorably. The device features compact size, no solid moving parts, and is made of common materials.
Harbor seal vibrissa morphology suppresses vortex-induced vibrations
Venue: The Journal of Experimental Biology

Harbor seals (Phoca vitulina) often live in dark and turbid waters, where their mystacial vibrissae, or whiskers, play an important role in orientation. Besides detecting and discriminating objects by direct touch, harbor seals use their whiskers to analyze water movements, for example those generated by prey fish or by conspecifics. Even the weak water movements left behind by objects that have passed by earlier can be sensed and followed accurately (hydrodynamic trail following). While scanning the water for these hydrodynamic signals at a swimming speed in the order of meters per second, the seal keeps its long and flexible whiskers in an abducted position, largely perpendicular to the swimming direction. Remarkably, the whiskers of harbor seals possess a specialized undulated surface structure, the function of which was, up to now, unknown. Here, we show that this structure effectively changes the vortex street behind the whiskers and reduces the vibrations that would otherwise be induced by the shedding of vortices from the whiskers (vortex-induced vibrations). Using force measurements, flow measurements and numerical simulations, we find that the dynamic forces on harbor seal whiskers are, by at least an order of magnitude, lower than those on sea lion (Zalophus californianus) whiskers, which do not share the undulated structure. The results are discussed in the light of pinniped sensory biology and potential biomimetic applications.
Rain-Harvesting in the Lizard, Phrynosoma cornutum: Behavior and Integumental Morphology
Venue: Journal of Herpetology

During rainstorms, Texas horned lizards in enclosures were observed to exhibit a stereotyped behavior termed "rain-harvesting." The behavior involves: (1) raising the abdomen in an arch; (2) splaying and extending the legs; (3) dorso-ventral flattening and lateral spreading of the body; (4) lowering the head and tail; (5) opening and closing the jaws; and (6) drinking water collected on the dorsal body surface. Ingestion of integumentally-derived water was verified by recovery of dyed water from the gut. SEM stereophotographs illustrate the interscalar channels through which water is carried, apparently by cap- illary action, over body surfaces to the jaws. During light rainfall water flow to the jaws occurs within interscalar channels, but during heavy rainfall gravitational sheet flow may increase the amount of water arriving at the jaws. This integumental rain-harvesting system is similar to reported interscalar water transport in two agamid lizards, Moloch horridus and Phrynocephalus helioscopus. Apparently, Phry- nosoma and P. helioscopus have similar behaviors for rain-harvesting. This is the first report to provide observations of a lizard obtaining water from natural precipitation for drinking by integumental inter- ception and transport.
How the Venus flytrap snaps
Venue: Nature

The rapid closure of the Venus flytrap (Dionaea muscipula) leaf in about 100 ms is one of the fastest movements in the plant kingdom. This led Darwin to describe the plant as “one of the most wonderful in the world”. The trap closure is initiated by the mechanical stimulation of trigger hairs. Previous studies have focused on the biochemical response of the trigger hairs to stimuli and quantified the propagation of action potentials in the leaves. Here we complement these studies by considering the post-stimulation mechanical aspects of Venus flytrap closure. Using high-speed video imaging, non-invasive microscopy techniques and a simple theoretical model, we show that the fast closure of the trap results from a snap-buckling instability, the onset of which is controlled actively by the plant. Our study identifies an ingenious solution to scaling up movements in non-muscular engines and provides a general framework for understanding nastic motion in plants.
Momilactone Sensitive Proteins in Arabidopsis thaliana
Venue: Natural Product Communications

The labdane-related diterpenoid, momilactone B has potent growth inhibitory activity and was demonstrated to play a particularly critical role in the allelopathy of rice (Oryza sativa L.). However, there is limited information available about the mode of action of momilactone B on the growth inhibition. The present research describes the effects of momilactone B on protein expression in the early development of Arabidopsis thaliana seedling, which was determined by two-dimensional electrophoresis and MALDI-TOFMS. Momilactone B inhibited the accumulation of subtilisin-like serine protease, amyrin synthase LUP2, β-glucosidase and malate synthase at 1 h after the momilactone application. Those proteins are involved in the metabolic turnover and the production of intermediates needed for cell structures resulting in plant growth and development. Momilactone B also inhibited the breakdown of cruciferin 2, which is essential for seed germination and seedling growth to construct cell structures. Momilactone B induced the accumulation of translationally controlled tumor protein, glutathione S-transferase and 1-cysteine peroxiredoxin 1. These proteins are involved in stress responses and increased stress tolerance. In addition, glutathione S-transferase has the activity of herbicide detoxification and 1-cysteine peroxiredoxin 1 has inhibitory activity for seed germination under unfavorable conditions. The present research suggests that momilactone B may inhibit the seedling growth by the inhibition of the metabolic turnover and the production of intermediates for cell structures. In addition, momilactone induced proteins associated with plant defense responses.
Rain-drinking behaviors of the Australian thorny devil (Sauria: Agamidae)
Venue: Journal of Herpetology

During natural and simulated rainfall, Moloch horridus used the cutaneous surface of its integument as a water-harvesting system to capture rain water for drinking. Circumstantial behavioral evidence, in combination with experimental studies (Withers, 1993), suggests that the capillary, interscalar, water-transport system of Moloch is also used to absorb water for drinking from rain-moistened substrates. Lizards rub their venters against wet substrates and dig sand onto their backs. This is a previously unreported behavior for water acquisition by lizards inhabiting arid regions. No stereotypic behavioral stance for rain harvesting, as seen in Phrynocephalus helioscopus and Phrynosoma cornutum, was observed in Moloch horridus
Effect of catch bonding on transport of cellular cargo by dynein motors.
Venue: Physical Review E

Recent experiments have demonstrated that dynein motors exhibit catch bonding behavior, in which the unbinding rate of a single dynein decreases with increasing force, for a certain range of force. Motivated by these experiments, we study the effect of catch bonding on unidirectional transport properties of cellular cargo carried by multiple dynein motors. We introduce a threshold force bond deformation (TFBD) model, consistent with the experiments, wherein catch bonding sets in beyond a critical applied load force. We find catch bonding can result in dramatic changes in the transport properties, which are in sharp contrast to kinesin-driven unidirectional transport, where catch bonding is absent. We predict that under certain conditions, the average velocity of the cellular cargo can actually increase as applied load is increased. We characterize the transport properties in terms of a velocity profile plot in the parameter space of the catch bond strength and the stall force of the motor. This plot yields predictions that may be experimentally accessed by suitable modifications of motor transport and binding properties.
Molecular mechanisms of synovial joint lubrication
Venue: Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology

Current models for lubrication of synovial joints, and the nature of the cartilage surface, are briefly recalled. Direct friction studies between polymers attached to surfaces are then considered, particularly the very recent demonstration of extreme friction reduction enabled by hydrated ions and by charged polymers. It is proposed that the extremely efficient lubrication observed in living joints arises from the presence of a brush-like phase of charged macromolecules at the surface of the superficial zone. This phase forms when charged macromolecules, including lubricin, superficial-zone protein, and aggrecan, cross the interface between the superficial zone and the synovial cavity as they are secreted into the synovium from within the bulk of the cartilage, and, in particular, the feasibility of such brush-like surface-phases is examined in some detail. The molecular mechanisms for the reduction in friction are proposed to be similar to those recently revealed using surface force balance studies on lubrication by charged brushes.