Array Of Hairs Research Articles

Influence of spider hair structure on acoustic response

It is well known that spiders have an extraordinary auditory sensitivity. However, significant differences in the acoustic impedance between air and solids (spiders) would reduce the acoustic energy transmitted from air to spiders, and by intuition this might result in a significant decrease in the acoustic sensitivity of spiders. This mechanism has been long troubled in researchers’ minds that how hunting spiders could have an outstanding auditory sensitivity. In this paper, the auditory sensing mechanisms of hunting spiders are studied by theoretical analysis and simulation. The results show that the acoustic impedance can be adjusted by spiders’ hairs with particular features to realize the acoustic impedance matching between air and spiders, which could make spiders’ hairs easily send signals to the nervous system of spiders, thus significantly promoting the acoustic energy transfer from air to spiders. Both the appropriate length and deflection angle of hairs are critical to determine the acoustic impedance/acoustic transmission coefficient. In parallel, verification test is carried out on an innovative bionic hair array. The experiment result shows that the acoustic impedance is significantly descended by the bionic hair array with the spiders' acoustic hairs' features, which provides a sufficient proof of the acoustic impedance matching by spiders' hairs. Consequently, this work clearly discloses the acoustic sensing mechanism for the extraordinary auditory sensitivity of hunting spiders, which may have a great significance for the development of artificial auditory technology and sound stealth devices.

Magnetic Tactile Sensor with Bionic Hair Array for Sliding Sensing and Object Recognition.

Due to the high application value in intelligent robots, tactile sensors with large sensing area and multi-dimensional sensing ability have attracted the attention of researchers in recent years. Inspired by bionics of hairs on human skin, a flexible tactile sensor based on magnetic cilia array is developed, showing extremely high sensitivity and stability. The upper layers of the sensor are multiple magnetic cilia containing magnetic particles, while the lower layer is a serpentine flexible circuit board with a magnetic sensor array. When magnetic cilia are bent under force, the magnetic sensor array can detect changes in the magnetic field, thereby the magnitude and direction of external force can be obtained. The proposed sensor has a resolution of 0.2 mN with a working range of 0-19.5 mN and can distinguish the direction of external force. The large sensing area and short response time make this sensor suitable for sliding tactile detection, and experiments show that the sensor can be also applied in object recognition with a success accuracy of 97%. In addition to the shape of objects, the sensor can identify whether there is magnetism inside objects, making it of significant value in intelligent robots and modern medicine.

The mechanics and interactions of electrically sensitive mechanoreceptive hair arrays of arthropods.

Recent investigations highlight the possibility of electroreception within arthropods through charged mechanosensory hairs. This discovery raises questions about the influence of electrostatic interaction between hairs and surrounding electrical fields within this sensory modality. Here, we investigate these questions by studying electrostatic coupling in arrays of hairs. We establish the notion of sensitivity contours that indicate regions within which point charges deflect hairs beyond a given threshold. We then examine how the contour’s shape and size and the overall hair behaviour change in response to variations in the coupling between hairs. This investigation unveils synergistic behaviours whereby the sensitivity of hairs is enhanced or inhibited by neighbouring hairs. The hair spacing and ratio of a system’s electrical parameters to its mechanical parameters influence this behaviour. Our results indicate that electrostatic interaction between hairs leads to emergent sensory properties for biologically relevant parameter values. The analysis raises new questions around the impact of electrostatic interaction on the current understanding of sensory hair processes, such as acoustic sensing, unveiling new sensory capabilities within electroreception such as amplification of hair sensitivity and location detection of charges in the environment.

Feeling for food: Can rostro-mental hair arrays sense hydrodynamic cues for foraging North Atlantic right whales?

North Atlantic right whales (NARWs; Eubalaena glacialis) possess an arrangement of fine hairs on the rostrum and chin that may be used for hydrodynamic sensing during feeding. These hairs occur across mysticete species and are known to possess adequate innervation in the subdermal follicle to support their consideration as sensory hairs (vibrissae). However, the small size of the hair structure with respect to the enormous scale of the animal's body has caused doubts regarding their utility and prompted speculation that the hairs may be vestigial or minimally functional. Here we show that NARW hairs occur in abundance on the leading surface of the head in a unique and characteristic arrangement. We consider the sensory hairs in context of the fluid environment in which this species forages and argue that the size of the hair is scaled to the size of the animal's small planktonic prey, thus suggesting that the hairs play an important role in the sensory ecology of these animals.

Hairy-Layer Friction Reduction Mechanism in the Honeybee Abdomen.

Abdominal sections of honeybees undergo numerous reciprocating motions during their lifetime. However, the overlapped contact areas adjacent to the abdominal sections have a shallow wear extent, a physical mechanism that remains obscure to date. Therefore, this study explored a biofrictional reduction model based on a solid surface texture and the hairy surface of the honeybee abdomen. We collected honeybee samples and observed their abdomens using a camera (Zeiss Stemi 508). Subsequently, we sliced these samples using a microtome and detected their microscopic friction. The exterior surface of the honeybee abdomen was not smooth but was distributed with a dense microvilli structure, which played a vital role in adjusting the friction reduction characteristics between the abdominal sections. When the adjacent abdominal sections moved relatively to each other, their upper and lower surfaces were not in direct rigid contact. Briefly, this study shows that the microscale hair arrays on the surface of the posterior abdominal segment can significantly reduce real contact area and friction, which considerably decreases wear or abrasion. The friction reduction mechanism alleviates the abrasion during the relative bending movement and saves a large amount of energy, which is essential for the honeybees' daily activities. This microtexture compliance friction reduction characteristic could be used to fabricate hierarchical surfaces for long-lasting friction reduction mechanisms, which increase the life of soft devices, including soft actuators and hinges.

Marine crustaceans with hairy appendages: Role of hydrodynamic boundary layers in sensing and feeding

Decapod crustaceans have appendages with an array of rigid hairs covered in chemo-receptors, used to sense and track food. Crustaceans directly influence the flow behavior by changing the speed of flow past the hairy surface, thereby manipulating the Reynolds number (Re). Hairs act either as a rake - diverting flow around the hair array, or as a sieve - filtering flow through the hairs. In our experiments, we uncover a third transitional phase: deflection - where the flow partially penetrates the hair array and is deflected laterally. We develop a reduced order model that predicts the flow phase based on the depth of the boundary layer on a single hair. This model with no fitting parameters agrees very well with our experimental data. Additionally, our model agrees well with measurements of both chemo-sensing and suspension-feeding crustaceans, and can be generalized for many different geometries.

Can plant-derived phytochemicals provide symptom relief for hair loss? A critical review.

It is known that hair growth disorders and hair loss can cause personal distress and affect well-being. Whilst clinical conditions remain a target for medical research, current research on hair follicle biology and hair growth control mechanisms also provides opportunities for a range of non-medical and cosmetic interventions that have a modulating effect on the scalp and follicle function. Furthermore, an improvement of the hair fibre characteristics (cuticle structure, cortex size and integrity) could add to the overall positive visual effect of the hair array. Since phytochemicals are a popular choice because of their traditional appeal, this review provides a critical evaluation of the available evidence of their activity for hair benefit, excluding data obtained from animal tests, and offers recommendations on improving study validity and the robustness of data collection in pre-clinical and clinical studies.

Tunable Multimodal Drop Bouncing Dynamics and Anti-Icing Performance of a Magnetically Responsive Hair Array.

Anti-icing materials that can efficiently limit ice formation have a strong potential to replace existing anti-icing techniques, such as Joule heating, chemical release, or mechanical removal, which are usually inefficient, expensive, and environmentally harmful. In this study, an anti-icing material based on a magnetically responsive hierarchical hair array that can actively modulate drop bouncing dynamics is presented. The magnetically responsive hair array exhibits an immediate and reversible structural bending motion in response to an external magnetic field. The array also exhibits superhydrophobicity, regardless of its tilt angle, due to the tapered geometry of the hairs and the multiscale surface roughness of the array. Due to its dynamic structure and water-repellent characteristics, the array can induce distinct multiple modes of drop bouncing behavior by adjusting its structural bending state in a reversible fashion. Three different types of bouncing behavior, namely, quasi-pancake bouncing, directional bouncing, and macrotexture-induced droplet fragmentation, can be obtained with the vertical, tilted, and fully bent hair arrays, respectively. We demonstrate that the dynamically controllable drop bouncing behavior of the magnetically responsive hierarchical array enables the efficient and robust prevention of ice formation and accumulation.

Bio-inspired hierarchical hair arrays with tunable adhesive superhydrophobicity

Inspired by the hierarchical seta arrays on the feet of gecko and the legs of water strider, two different microstructures including cylindrical hair arrays and coniform hair arrays have been fabricated by reactive ion etching combined with colloidal lithography. Interestingly, all the artificial hair arrays are sculptured with elaborate nanogrooves, leading to a unique hierarchical structure. Inspired by the novel hierarchical structures, the contrastive experimental research for their wetting properties was carried out by means of optical contact angle measurement. The results show that after fluorination, both of the two hair arrays exhibit excellent superhydrophobicity, but different adhesive force towards water. These tunable adhesive superhydrophobicity may be attributed to the different morphologies of the hair arrays. Based on these properties, a “mechanical hand” to transport small water droplets from a superhydrophobic surface to a hydrophobic or a hydrophilic surface without any loss or contamination was realized.

A tale of two antennules: the performance of crab odour-capture organs in air and water.

Odour capture is an important part of olfaction, where dissolved chemical cues (odours) are brought into contact with chemosensory structures. Antennule flicking by marine crabs is an example of discrete odour capture (sniffing) where an array of chemosensory hairs is waved through the water to create a flow-no flow pattern based on a narrow range of speeds, diameters of and spacings between hairs. Changing the speed of movement and spacing of hairs at this scale to manipulate flow represents a complicated fluid dynamics problem. In this study, we use numerical simulation of the advection and diffusion of a chemical gradient to reveal how morphological differences of the hair arrays affect odour capture. Specifically, we simulate odour capture by a marine crab (Callinectes sapidus) and a terrestrial crab (Coenobita rugosus) in both air and water to compare performance. We find that the antennule morphologies of each species are adaptions to capturing odours in their native habitats. Sniffing is an important part of odour capture for marine crabs in water where the diffusivity of odorant molecules is low and flow through the array is necessary. On the other hand, flow within the hair array diminishes odour-capture performance in air where diffusivities are high. This study highlights some of the adaptations necessary to transition from water to air.

Unique wing scale photonics of male Rajah Brooke's birdwing butterflies.

BackgroundUltrastructures in butterfly wing scales can take many shapes, resulting in the often striking coloration of many butterflies due to interference of light. The plethora of coloration mechanisms is dazzling, but often only single mechanisms are described for specific animals.ResultsWe have here investigated the male Rajah Brooke’s birdwing, Trogonoptera brookiana, a large butterfly from Malaysia, which is marked by striking, colorful wing patterns. The dorsal side is decorated with large, iridescent green patterning, while the ventral side of the wings is primarily brown-black with small white, blue and green patches on the hindwings. Dense arrays of red hairs, creating a distinct collar as well as contrasting areas ventrally around the thorax, enhance the butterfly’s beauty. The remarkable coloration is realized by a diverse number of intricate and complicated nanostructures in the hairs as well as the wing scales. The red collar hairs contain a broad-band absorbing pigment as well as UV-reflecting multilayers resembling the photonic structures of Morpho butterflies; the white wing patches consist of scales with prominent thin film reflectors; the blue patches have scales with ridge multilayers and these scales also have centrally concentrated melanin. The green wing areas consist of strongly curved scales, which possess a uniquely arranged photonic structure consisting of multilayers and melanin baffles that produces highly directional reflections.ConclusionRajah Brooke’s birdwing employs a variety of structural and pigmentary coloration mechanisms to achieve its stunning optical appearance. The intriguing usage of order and disorder in related photonic structures in the butterfly wing scales may inspire novel optical materials as well as investigations into the development of these nanostructures in vivo.

Zinc-Air Batteries: Flexible Rechargeable Zinc-Air Batteries through Morphological Emulation of Human Hair Array (Adv. Mater. 30/2016).

On page 6421, Z. Chen and co-workers describe an electrically rechargeable, nanoarchitectured air electrode that morphologically emulates a human-hair array for solid-state zinc-air batteries. Grown directly on a stainless-steel mesh, the hair-like array can effectively catalyze molecular oxygen to water. Batteries equipped with this electrode show tangible benefits, including improved flexibility and performance.

Pretarsus structure in relation to climbing ability in the ants Brachyponera sennaarensis and Daceton armigerum

We studied the external and internal pretarsus structure of the ants Brachyponera sennaarensis and Daceton armigerum in relation to their very different climbing ability. B. sennaarensis is a ground-dwelling species that is not able to climb vertical smooth walls. They have a pair of straight pretarsal claws with an average claw tip angle of 56 degrees, while the ventral tarsal surface lacks fine hairs that touch the substrate. They have no adhesive pad on the vestigial arolium, while the arolium gland is very small. D. armigerum, on the other hand, is an arboreal and thus well-climbing species with a very strong grip on the substrate. Their pretarsal claws are very hooked, with a claw tip angle around 75 degrees. They have dense arrays of fine hairs on the ventral tarsal surface, a well-developed arolium and arolium gland. These clearly different morphological characteristics are in line with the opposite climbing performance of both species.

Flexible Rechargeable Zinc-Air Batteries through Morphological Emulation of Human Hair Array.

An electrically rechargeable, nanoarchitectured air electrode that morphologically emulates a human hair array is demonstrated in a zinc-air battery. The hair-like array of mesoporous cobalt oxide nanopetals in nitrogen-doped carbon nanotubes is grown directly on a stainless-steel mesh. This electrode produces both flexibility and improved battery performance, and thus fully manifests the advantages of flexible rechargeable zinc-air batteries in practical applications.

The nanotipped hairs of gecko skin and biotemplated replicas impair and/or kill pathogenic bacteria with high efficiency.

We show that gecko microspinules (hairs) and their equivalent replicas, bearing nanoscale tips, can kill or impair surface associating oral pathogenic bacteria with high efficiency even after 7 days of repeated attacks. Scanning Electron Microscopy suggests that there is more than one mechanism contributing to cell death which appears to be related to the scaling of the bacteria type with the hair arrays and accessibility to the underlying nano-topography of the hierarchical surfaces.

Do terrestrial hermit crabs sniff? Air flow and odorant capture by flicking antennules.

Capture of odorant molecules by olfactory organs from the surrounding fluid is the first step of smelling. Sniffing intermittently moves fluid across sensory surfaces, increasing delivery rates of molecules to chemosensory receptors and providing discrete odour samples. Aquatic malacostracan crustaceans sniff by flicking olfactory antennules bearing arrays of chemosensory hairs (aesthetascs), capturing water in the arrays during downstroke and holding the sample during return stroke. Terrestrial malacostracans also flick antennules, but how their flicking affects odour capture from air is not understood. The terrestrial hermit crab, Coenobita rugosus, uses antennules bearing shingle-shaped aesthetascs to capture odours. We used particle image velocimetry to measure fine-scale fluid flow relative to a dynamically scaled physical model of a flicking antennule, and computational simulations to calculate diffusion to aesthetascs by odorant molecules carried in that flow. Air does not flow into the aesthetasc array during flick downstrokes or recovery strokes. Odorants are captured from air flowing around the outside of the array during flick downstrokes, when aesthetascs face upstream and molecule capture rates are 21% higher than for stationary antennules. Bursts of flicking followed by pauses deliver discrete odour samples to olfactory sensors, causing intermittency in odour capture by a different mechanism than aquatic crustaceans use.

Insects have hairy eyes that reduce particle deposition

An insect’s eyes may make up to 40% of its body’s surface, and are in danger of being coated by foreign particles such as dust and pollen. To protect them, several insect species possess an array of ocular hairs evenly spaced between each photoreceptor unit. Although these hairs have been observed for over 50 years, their purpose remains a mystery. In this study, we elucidate the function of ocular hairs using a combination of experiments, numerical simulation and micro-fabrication. We measure the eyes of 18 species of insects and find that the length of their ocular hairs is equal to their spacing. We conduct wind tunnel experiments using both an insect eye mimic and an at-scale fabricated micro-pillar array of the same dimensions as the insect eye. Our experiments and simulations show that ocular hairs reduce airflow at the eye surface by up to 90%. We conclude that ocular hairs act similarly to mammalian eyelashes: as insects fly, ocular hairs deflect incoming air and create a zone of stagnant air. Airflow and particle deposition are reduced dramatically, while light is only minimally occluded. Micro-scale ocular hairs may find application in the deployment of sensors outdoors, for which accumulation of airborne dust and pollen has no current solution.

On Heels and Toes: How Ants Climb with Adhesive Pads and Tarsal Friction Hair Arrays.

Ants are able to climb effortlessly on vertical and inverted smooth surfaces. When climbing, their feet touch the substrate not only with their pretarsal adhesive pads but also with dense arrays of fine hairs on the ventral side of the 3rd and 4th tarsal segments. To understand what role these different attachment structures play during locomotion, we analysed leg kinematics and recorded single-leg ground reaction forces in Weaver ants (Oecophylla smaragdina) climbing vertically on a smooth glass substrate. We found that the ants engaged different attachment structures depending on whether their feet were above or below their Centre of Mass (CoM). Legs above the CoM pulled and engaged the arolia (‘toes’), whereas legs below the CoM pushed with the 3rd and 4th tarsomeres (‘heels’) in surface contact. Legs above the CoM carried a significantly larger proportion of the body weight than legs below the CoM. Force measurements on individual ant tarsi showed that friction increased with normal load as a result of the bending and increasing side contact of the tarsal hairs. On a rough sandpaper substrate, the tarsal hairs generated higher friction forces in the pushing than in the pulling direction, whereas the reverse effect was found on the smooth substrate. When the tarsal hairs were pushed, buckling was observed for forces exceeding the shear forces found in climbing ants. Adhesion forces were small but not negligible, and higher on the smooth substrate. Our results indicate that the dense tarsal hair arrays produce friction forces when pressed against the substrate, and help the ants to push outwards during horizontal and vertical walking.

Wetting properties of cosmetic polymeric solutions on hair tresses

The objective of the present work is to investigate wetting of hair tresses with the solutions of two polyacrylate polymers broadly used in cosmetic products. Wetting properties of the neutralized Aculyn-22™ (A22) and Aculyn-33™ (A33) polymer solutions on dry hair tresses are studied. Wetting behaviour on the dry undamaged hair tresses is drastically different between the two polymers and, in a first approximation, not directly linked with their bulk rheology. In the case of A22 the droplet spreads and remains on the tress after spreading for at least half an hour, during which it slowly evaporates and possibly penetrates inside the hair. For A33 fast penetration of the droplet inside the hair tress is observed when the advancing contact angle reaches a critical value of about 60°. It can be attributed to the so-called Cassie–Wenzel wetting transition, in which the liquid starts to penetrate inside the hair array.

Ultrastructure of the fossula spongiosa and pretarsus in Haematoloecha nigrorufa (Stål) (Hemiptera: Heteroptera: Reduviidae: Ectrichodinae).

The ultrastructure of the fossula spongiosa and pretarsus of adult Haematoloecha nigrorufa (Stål) (Heteroptera: Reduviidae: Ectrichodinae) was examined for the first time using scanning electron microscope. The fossula spongiosa of H. nigrorufa is located on the ventral surface of the distal part of the tibia of both the fore- and midlegs. The area of the fossula spongiosa on the female foreleg is approximately 251338.88 μm(2), while the area of the fossula spongiosa on the male foreleg is markedly smaller, only about 196548.98 μm(2). For both genders the area of the fossula spongiosa on the foreleg is approximately 1.50 times as large as that on the midleg. Externally, the ventral surface of the fossula spongiosa is covered by a large number of tenent hairs that are evenly interspersed with a few mechanosensory setae. Each tenent hair consists of two parts: a hair shaft and an apical plate. A tenent hair is 22.58 ± 1.60 μm in length, 1.90 ± 0.09 μm in shaft diameter, and 10.90 ± 0.63 μm(2) in apical plate area. Morphologically, the tenent hairs are similar and constitute a nearly uniform hair array on the ventral side of the fossula spongiosa. The density of tenent hairs is about 4.46 ± 0.35 hairs per 100 μm(2) and the total number of tenent hairs is more than ten thousand on the fossula spongiosa of the female foreleg. These tenent hairs are presumed to function as adherence during locomotion or prey capture of the assassin bugs. In addition, scanning micrographs and descriptions for the pretarsus are also given.