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In this study, low-cost and eco-friendly hydroxyapatite (HA) minerals were extracted from scales of Tilapia fish (Oreochromis mossambicus). After calcination, fish-scale extracted powder was further confirmed to be HA by X-ray diffraction with mean particle size of 5.96 μm determined by particle size analyzer. The calcined powder was utilized as the raw material and combined with chitosan (CS) to synthesize composite scaffolds by freeze casting and cross-linking. Mercury porosimetry results showed that the scaffolds possessed hierarchical porous structure. Microstructural features characterized by SEM revealed unidirectional channel structures with channel sizes ranged from 10 to 100 μm and 1 to 50  μm for scaffolds freeze-casted at 2 ℃/min and 5 ℃/min cooling rates, respectively. The adsorption kinetics of HA/CS composite scaffolds with varying channel sizes were investigated by both batch and fixed-bed processes with different Pb(П) initial concentrations (100 and 1000 mg/L). The adsorption capability was optimized by tuning the cooling rates and the maximum adsorption amount could reach 75-570 mg/g in batch process and 94 mg/g in fixed bed process. In summary, the HA/CS composite scaffolds showed great capability to remove heavy metal ions from waste water and their tunable channel sizes could be applied in suitable fields under both statistic and flowing conditions., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The scaled skin of fish is an intricate system that provides mechanical protection against hard and sharp puncture, while maintaining the high flexural compliance required for unhindered locomotion. This unusual combination of local hardness and global compliance makes fish skin an interesting model for bioinspired protective systems. In this work we investigate the flexural response of whole teleost fish, and how scales may affect global flexural stiffness. A bending moment is imposed on the entire body of a striped bass (Morone saxatilis). Imaging is used to measure local curvature, to generate moment-curvature curves as function of position along the entire axis of the fish. We find that the flexural stiffness is the highest in the thick middle portion of the fish, and lowest in the caudal and rostral ends. The flexural response is nonlinear, with an initial soft response followed by significant stiffening at larger flexural deformations. Low flexural stiffness at low curvatures promotes efficient swimming, while higher stiffness at high curvatures enables a possible tendon effect, where the mechanical energy at the end of a stroke is stored in the form of strain energy in the fish skin. To assess the contribution of the scales to stiffening we performed flexural tests with and without scales, following a careful protocol to take in account tissue degradation and the effects of temperature. Our findings suggest that scales do not substantially increase the whole body flexural stiffness of teleost fish over ranges of deformations which are typical of swimming and maneuvering. Teleost scales are thin and relatively flexible, so they can accommodate large flexural deformations. This finding is in contrast to the bulkier ganoid scales which were shown in previous reports to have a profound impact of global flexural deformations and swimming in fish like gar or Polypterus., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Pangolin scales form a durable armor whose hierarchical structure offers an avenue towards high performance bio-inspired materials design. In this study, the fracture resistance of African pangolin scales is examined using single edge crack three-point bend fracture testing in order to understand toughening mechanisms arising from the structures of natural mammalian armors. In these mechanical tests, the influence of material orientation and hydration level are examined. The fracture experiments reveal an exceptional fracture resistance due to crack deflection induced by the internal spatial orientation of lamellae. An order of magnitude increase in the measured fracture resistance due to scale hydration, reaching up to ~ 25kJ/m 2 was measured. Post-mortem analysis of the fracture samples was performed using a combination of optical and electron microscopy, and X-ray computerized tomography. Interestingly, the crack profile morphologies are observed to follow paths outlined by the keratinous lamellae structure of the pangolin scale. Most notably, the inherent structure of pangolin scales offers a pathway for crack deflection and fracture toughening. The results of this study are expected to be useful as design principles for high performance biomimetic applications., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Biomimetic scales are known to substantially alter the mechanics response of the underlying substrate engendering complex nonlinearities that can manifest even in small deformations due to scales interaction. This interaction is typically modeled using a-priori homogenization with an enforced periodicity of engagement. Such a framework is fairly useful especially when dealing with the structural length scale which is at least one order of magnitude greater than the scales themselves since individual tracking of a large number of scales become insurmountable. On the other hand, this scheme makes several assumptions whose validity has not yet been investigated including infinite length of the substrate and rigidity of the scales. The validity of these assumptions and the accuracy and limitations of associated analytical models are investigated. Finite element based numerical studies were carried out to identify the critical role of edge effects and other non-ideal behavior such as violation of periodicity and nonlinear constitutive response on scale rotation. Our investigation shows that several important quantities show a strong saturation characteristic which justify many of the simplifying assumptions whereas others need much greater care., (Copyright © 2017 Elsevier Ltd. All rights reserved.)