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This paper explores the use of Two-Dimensional sinusoidal surface features to delay transition and/or reduce drag. The authors, in this paper demonstrated that the presence of low amplitude sinusoidal surface features might damp the disturbances in the laminar boundary layer, reduce wall shear stress and maintain laminar flow for longer than a conventional flat plate. The hypothesis of the paper is inspired by the simplification of the dermal denticle on the surface of the shark-skin. Simulations are carried out using the Transition SST model in FLUENT based on the evidences of the transition model being suitable for a wider variety of high curvature scenarios. The surface waves are simulated for different amplitudes and wavelengths and their impact on transition onset and drag reduction are quantified at different velocities. Results presented in this paper indicate that a transition delay of 10.8% and a drag reduction of 5.2% are achievable. Furthermore, this paper adds credence to the notion that biomimicry is a very promising avenue for future drag reducing methods.

The skin of fast-swimming sharks exhibits riblet structures aligned in the direction of flow that are known to reduce skin friction drag in the turbulent-flow regime. Structures have been fabricated for study and application that replicate and improve upon the natural shape of the shark-skin riblets, providing a maximum drag reduction of nearly 10 per cent. Mechanisms of fluid drag in turbulent flow and riblet-drag reduction theories from experiment and simulation are discussed. A review of riblet-performance studies is given, and optimal riblet geometries are defined. A survey of studies experimenting with riblet-topped shark-scale replicas is also given. A method for selecting optimal riblet dimensions based on fluid-flow characteristics is detailed, and current manufacturing techniques are outlined. Due to the presence of small amounts of mucus on the skin of a shark, it is expected that the localized application of hydrophobic materials will alter the flow field around the riblets in some way beneficial to the goals of increased drag reduction.

The epidermis of Chondrichthyan fishes consists of dermal denticles with production of minimal but protein-rich mucus that collectively, influence the attachment and biofilm development of microbes, facilitating a unique epidermal microbiome. Here, we use metagenomics to provide the taxonomic and functional characterization of the epidermal microbiome of the Triakis semifasciata (leopard shark) at three time-points collected across 4 years to identify links between microbial groups and host metabolism. Our aims include (1) describing the variation of microbiome taxa over time and identifying recurrent microbiome members (present across all time-points); (2) investigating the relationship between the recurrent and flexible taxa (those which are not found consistently across time-points); (3) describing the functional compositions of the microbiome which may suggest links with the host metabolism; and (4) identifying whether metabolic processes are shared across microbial genera or are unique to specific taxa. Microbial members of the microbiome showed high similarity between all individuals (Bray–Curtis similarity index = 82.7, where 0 = no overlap, 100 = total overlap) with the relative abundance of those members varying across sampling time-points, suggesting flexibility of taxa in the microbiome. One hundred and eighty-eight genera were identified as recurrent, including Pseudomonas , Erythrobacter , Alcanivorax , Marinobacter , and Sphingopxis being consistently abundant across time-points, while Limnobacter and Xyella exhibited switching patterns with high relative abundance in 2013, Sphingobium and Sphingomona in 2015, and Altermonas , Leeuwenhoekiella , Gramella , and Maribacter in 2017. Of the 188 genera identified as recurrent, the top 19 relatively abundant genera formed three recurrent groups. The microbiome also displayed high functional similarity between individuals (Bray–Curtis similarity index = 97.6) with gene function composition remaining consistent across all time-points. These results show that while the presence of microbial genera exhibits consistency across time-points, their abundances do fluctuate. Microbial functions however remain stable across time-points; thus, we suggest the leopard shark microbiomes exhibit functional redundancy. We show coexistence of microbes hosted in elasmobranch microbiomes that encode genes involved in utilizing nitrogen, but not fixing nitrogen, degrading urea, and resistant to heavy metal.

With the global population growing, energy demand has increased drastically. Simultaneously, environmental concerns have been increasing at an alarming rate. In transportation systems such as pipelines and ships, the resistance caused by friction is a major factor leading to energy loss. This not only leads to high energy consumption but also hinders improving the overall efficiency of transportation processes. Therefore, finding a solution to minimize this energy loss has emerged as a critical research area among scholars. A viable solution inspired by the unique structures in nature is deemed an effective drag reduction method. This paper outlines the bionic structures of earthworms, sharks, and dolphins and discusses their theory and mechanism for reducing drag. Furthermore, this paper compares recent approaches employing bionic drag–reduction interfaces based on earthworm, shark, and dolphin body structures. The applications of bionic interfacial drag reduction materials in agriculture, transportation, and industry are also analyzed, along with a summary of the limitations and challenges associated with bionic interfacial drag reduction. Finally, the authors look forward to future research directions and application prospects of bionic interfacial drag reduction materials.

Shark skin surfaces show non-smoothness characteristics due to the presence of a riblet structure. In this study, biomimetic shark skin was prepared by using the polydimethylsiloxane (PDMS)-embedded elastomeric stamping (PEES) method. Scanning electron microscopy (SEM) was used to examine the surface microstructure and fine structure of shark skin and biomimetic shark skin. To analyse the hydrophobic mechanism of the shark skin surface microstructure, the effect of biomimetic shark skin surface microstructure on surface wettability was evaluated by recording water contact angle. Additionally, protein adhesion experiments and anti-algae adhesion performance testing experiments were used to investigate and evaluate the anti-biofouling properties of the surface microstructure of biomimetic shark skin. The recorded values of the water contact angle of differently microstructured surfaces revealed that specific microstructures have certain effects on surface wettability. The anti-biofouling properties of the biomimetic shark skin surface with microstructures were superior to a smooth surface using the same polymers as substrates. Moreover, the air layer fixed on the surface of the biomimetic shark skin was found to play a key role in their antibiont adhesion property. An experiment into drag reduction was also conducted. Based on the experimental results, the microstructured surface of the prepared biomimetic shark skin played a significant role in reducing drag. The maximum of drag reduction rate is 12.5%, which is higher than the corresponding maximum drag reduction rate of membrane material with a smooth surface.

In this study, a novel but simple biomimetic turbulent drag reduction topology is proposed, inspired by the special structure of shark skin. Two effective, shark skin-inspired, ribletted surfaces were designed, their topologies were optimized, and their excellent drag reduction performances were verified by large eddy simulation. The designed riblets showed higher turbulent drag reduction behavior, e.g., 21.45% at Re = 40,459, compared with other experimental and simulated reports. The effects of the riblets on the behavior of the fluid flow in pipes are discussed, as well as the mechanisms of fluid drag in turbulent flow and riblet drag reduction. Riblets of various dimensions were analyzed and the nature of fluid flow over the effective shark skin surface is illustrated. By setting up the effective ribletted surface on structure’s surface, the shark skin-inspired, biomimetic, ribletted surface effectively reduced friction resistance without external energy support. This method is therefore regarded as the most promising drag reduction technique.

The marvels of the slippery and clean sharkskin have inspired the development of many clinical and engineering products, although the mechanisms of interfacial interaction between the sharkskin and water have yet to be fully understood. In the present research, a methodology was developed to evaluate morphological parameters and to enable studying the effects of scale orientation on the fluidic behavior of water. The scale orientation of a shark skin was defined as the angle between the ridges and fluid flow direction. Textured surfaces with a series orientation of scales were designed and fabricated using 3D printing of acrylonitrile butadiene styrene (ABS). The fluid drag performance was evaluated using a rheometer. Results showed that the shark–skin-like surface with 90 degree orientation of scales exhibited the lowest viscosity drag. Its maximum viscosity reduction was 9%. A viscosity map was constructed based on the principals of fluid dynamic. It revealed that the drag reduction effect of a shark-skin-like surface was attributed to the low velocity gradient. This was further proven using diamond nitrogen-vacancy sensing where florescent diamond particles were distributed evenly when the velocity gradient was at the lowest. This understanding could be used as guidance for future surface design.

We manufactured the 3D-printed prototypes with increased wear resistance using a combination of the following: biomimetic design (the shark skin was used as a natural object to follow), 3D-printing technological parameter regulation, rational choice of polymer matrix, dispersed filling ingredients and items’ surface gas-phase modification technique. It was established that the bulk modification of the PETG filament with montmorillonite, graphite nano-plates, and other ingredients can reduce the 3D-printed prototypes’ wear by up to eight times. The gas-phase fluorination of the product’s surface provides a decrease in the rest friction coefficient and temperature in the “indentor-3D-printed disk” contact pair. We obtained the texture models and quantified the degree of similarity between the shark skin and the 3D-printed prototypes’ surfaces.

Shark skin has for many years inspired engineers to produce biomimetic structures reducing surface drag or acting as an anti-fouling layer. Both effects are presumed to be consequences of the structure of shark skin that is composed of arrays of so-called dermal denticles. However, the understanding of the full functional role of the dermal denticles is still a topic of research. We report optical microscopy and scanning electron microscopy of dermal denticles from three slowly swimming shark species for which the functional role of the dermal denticles is suggested as one of defense (possibly understood as anti-fouling) and/or abrasion strength. The three species are Greenland shark (Somnosius microcephalus), small-spotted catshark (Scyliorhinus canicula) and spiny dogfish (Squalus acanthias). Samples were taken at over 30 different positions on the bodies of the sharks. In addition, we demonstrate that the flow pattern near natural shark skin can be measured by micro-PIV (particle image velocimetry). The microfluidic experiments are complemented by numerical flow simulations. Both visualize unsteady flow, small eddies, and recirculation bubbles behind the natural dermal denticles.

Surgical electrodes are frequently associated with disadvantages such as high surface adhesion and severe thermal damage to adjacent normal tissues, which threaten operation quality and patient safety. In this study, by mimicking the micromorphology and bio-anti-adhesion of shark skin, we proposed a strategy that utilized nanoscale aluminium oxide (Al 2 O 3 ) films deposited on bioinspired shark skin (BSS) microstructures to design a composite surface (Al 2 O 3 @BSS) and integrated it into both flat sides of the surgical electrodes. Micro/nano-manufacturing of the Al 2 O 3 @BSS surface was sequentially accomplished using nanosecond laser texturing, atomic layer deposition, and low-temperature annealing, endowing it with excellent blood-repellent properties. Visualisation experiments revealed that the tensile stress gradient of the blood coagulum with increasing thickness under a thermal field prompted it to separate from the Al 2 O 3 @BSS surface, resulting in anti-adhesion. Furthermore, it was observed for the first time that Al 2 O 3 films could transiently excite discharge along a dielectric surface (DADS) to ablate tissues while suppressing Joule heat, thereby minimising thermal damage. A combination of ex vivo tissue and living mouse experiments demonstrated that the Al 2 O 3 @BSS electrodes exhibited optimal comprehensive performance in terms of anti-adhesion, damage minimisation, and drag reduction. In addition, the Al 2 O 3 @BSS electrodes possessed remarkable antibacterial efficacy against E. coli and S. aureus . The proposed strategy can meet the extreme application requirements of surgical electrodes to improve operation quality and offer valuable insights for future studies. Surface blood-repellency was achieved by depositing Al 2 O 3 films on bioinspired shark skin microstructures. Blood-repellent surfaces were sequentially fabricated by laser texturing, atomic layer deposition, and low-temperature annealing. A tensile stress gradient was generated by blood coagulum under thermal field to promote anti-adhesion. Electrode transient discharges were excited by Al 2 O 3 films, suppressing Joule heating. Blood-repellent surfaces were applied in surgical electrodes to enhance comprehensive performance.