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An understanding of the relationship between the structure, mechanical properties and functions of teeth is required regarding the development of effective and durable bio-inspired synthetic dental materials. Many studies have investigated this relationship in many species. However, few studies have been conducted on the teeth of Serrasalmidae fishes. The family of Serrasalmidae, though, offers an excellent opportunity to study this relationship because of the diversity of their diet. 

The tooth consists of three distinct layers which are called (going from the center of the tooth to the outside): the pulp, the dentin and the enamel/enameloid. In some fishes, including those of the family Serrasalmidae, an additional superficial layer called the cuticle is also present. 

The topic of the present thesis is to investigate structural and mechanical adaptation of the enameloid in two Serrasalmidae fishes having different diets: the carnivorous Pygocentrus nattereri, preferentially feeding on soft prey, and the herbivorous pacu Piaractus brachypomus, preferentially eating hard shells.

Enameloid microstructure is first characterized. Microscopic analysis of fractured teeth as well as surface etching performed on teeth sections allow identifying precisely the structure of the enameloid in the two species. Comparison between the structures found in the two species highlights that despite their different diets, no structural differences are observed between species with different feeding strategies (slicing vs. crushing). The enameloid of both fishes possesses a two-part organization. The inner enameloid is characterized by hydroxyapatite fiber bundles oriented and curved in a random manner forming a very sophisticated interlocking structure. The outer enameloid is organized with hydroxyapatite bundles aligned with each outer and oriented either parallel or perpendicular to the tooth surface, depending on the region analyzed.

Second, the potential correlation between microstructure and mechanical properties is investigated through the assessment of local fracture behavior. Indeed, fracture resistance is an essential feature allowing the enameloid and, in general, the tooth to avoid catastrophic failure when cracks nucleate on the other surface due to repeated cycles of chewing. High load indentation tests in combination with scanning microscopy are used to explore fracture properties of the different teeth. Although the difference is not significant, a quantitative evaluation of the fracture toughness as well as a qualitative observation of the cracks morphology demonstrates that inner enameloid possesses a higher resistance to crack initiation and propagation than the outer enameloid. Furthermore, indentation-based cracks invariably propagate along the internal interfaces, especially at the interface between the hydroxyapatite bundles, and that several extrinsic toughening mechanisms, such as crack deflection/curvature and un-cracked hydroxyapatite bundles are used by the enameloid to increase fracture resistance.

Novel addictive manufacturing routes such as freeze casting or magnetically assisted manufacturing may allow the fabrication of ceramic scaffolds replicating the structure seeing in the enameloid to improve fracture resistance of synthetic teeth.

Enameloid, Serrasalmidae, Structure, Scanning microscopy, Indentation, Fracture toughness, Toughening mechanisms --- Ingénierie, informatique & technologie > Ingénierie civile

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Steels and their heat treatment are still very important in modern industry because most industrial components are made from these materials. The proper choice of steel grades along with their suitable processing makes it possible to reduce the weight of the components, which is closely related to energy and fuel savings. This has decisive importance in branches such as the automotive, transport, consumer industries. A great number of novel heat- and surface-treatment techniques have been developed over the past three decades. These techniques involve, for example, vacuum treatment, sub-zero treatment, laser/electron beam surface hardening and alloying, low-pressure carburizing and nitriding, and physical vapour deposition. This Special Issue contains a collection of original research articles on not only advanced heat-treatment techniques—carburizing and sub-zero treatments—but also on the microstructure–property relationships in different ferrous alloys.

Vanadis 6 die steel --- surface finish --- nitriding --- PVD coating --- toughness --- fractography --- cryogenic treatment --- cryo-treatment --- mechanical properties --- microstructure --- cryo-processing --- 20Cr2Ni4A --- vacuum carburizing --- ion implantation --- rare earths --- catalysis --- carbon diffusion --- vanadis 6 steel --- sub-zero treatment at −75 °C --- hardness --- fracture toughness --- grade 92 steel weldment --- post-welding heat treatment --- tensile straining --- hydrogen embrittlement --- metallography and fractography --- ledeburitic tool steels --- carburizing --- rare-earth element pre-implantation --- sub-zero treatments

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Today, mainly man-made materials, such as carbon and glass fibers, are used to produce composite parts in aviation. Renewable materials, such as natural fibers or bio-sourced resin systems, have not yet found their way into aviation. The project ECO-COMPASS aims to evaluate the potential applications of ecologically improved composite materials in the aviation sector in an international collaboration of Chinese and European partners. Natural fibers such as flax and ramie will be used for different types of reinforcements and sandwich cores. Furthermore, bio-based epoxy resins to substitute bisphenol-A based epoxy resins in secondary structures are under investigation. Adapted material protection technologies to reduce environmental influence and to improve fire resistance are needed to fulfil the demanding safety requirements in aviation. Modelling and simulation of chosen eco-composites aims for an optimized use of materials while a Life Cycle Assessment aims to prove the ecological advantages compared to synthetic state-of-the-art materials. This Special Issue provides selected papers from the project consortium partners.

physical properties --- n/a --- plant fiber --- fracture toughness --- eco-composite --- functional composites --- flax fibre --- balsa --- bio-composites --- hybrid composite --- interface --- itaconic acid --- sandwich structures --- nonwoven --- flax --- engineering applications --- paper --- carbon nanotubes --- composite --- recycled carbon fibre --- poly-lactic acid --- rosin acid --- aviation sector --- crack sensing --- bio-sourced epoxy --- life cycle assessment --- natural fibre --- electrical properties --- glass fibre --- polymer nanocomposites --- environmental impacts --- multi-scale modeling --- function integrated interleave --- ramie fiber --- bio-based epoxy --- hybrid --- fabric --- sound absorption --- microstructures --- thermosetting resin --- wet-laying --- electrical conductivity --- green composite

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Biomaterials is currently one of the most important fields of study. This is because of the high degree of interdisciplinarity and the many practical solutions it provides in relation to medicine, biology, chemistry, and physics. This Special Issue provides readers with research from the domain of composite biomaterials in different applications, from controlled drug release systems to tissue engineering.

History of engineering & technology --- PMMA --- zirconia (ZrO2) --- nanocomposite --- denture base --- flexural strength --- impact strength --- fracture toughness --- hardness --- graphene oxide --- silicone rubber --- composite materials --- antifouling --- harmonic motion --- corn straw --- pretreatment --- dyeing --- chemical structure --- tensile properties --- UV barrier --- water-resistance --- polylactic acid --- hydroxyapatite --- composite films --- industrial bamboo residue --- holocellulose aerogel --- hydrophobicity --- fire resistance --- thermal insulation material --- nucleating agent --- isotactic polypropylene --- transcrystallinity --- natural fibres --- Tencel™ --- membrane --- cellulose --- water purification --- tissue engineering --- magnetic nanoparticles --- composite --- DDS --- hyperthermia --- collagen --- scaffolds --- membranes --- hydrogels --- whey protein fibrils --- carbon nanotubes --- carbon nano-onions --- composites --- interaction --- n/a

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Biomaterials—the materials used for the manufacturing of medical devices— are part of everyday life. Each one of us has likely had the experience of visting a dentist’s office, where a number of biomaterials are used temporarily or permanently in the mouth. Devices that are more complex are used for to support, heal, or replace living tissues or organs in the body that are suffering or compromised by different conditions. The materials used in their construction are metals and metallic alloys, polymers—ranging from elastomers to adhesives—and ceramics.Within these three cases, there are materials that are inert in the living environment, that perform an active function, or that are dissolved and resorbed by the metabolic pathways. Biomaterials are the outcome of a dynamic field of research that is driven by a growing demand and by the competition among the manufacturers of medical devices, with innovations improving the performance of existing devices and that contribute to the development of new ones. The collection of papers forming this volume have one particular class of of biomaterial in common, ceramic (bioceramic) composites, which as so far been used in applications such as orthopaedic joint replacement as well as in dental implants and restorations and that is being intensively investigated for bone regeneration applications. Today’s bioceramic composites (alumina–zirconia) are the golden standard in joint replacements. Several manufracturers have proposed different zirconia–alumina composites for use in hip, knee, and shoulder joint replacements, with several other innovative devices also being under study. In addition, bioceramic composites with innovative compositions are under development and will be on the market in years to come. Something that is especially interesting is the application of bioceramic composites in the regeneration of bone tissues. Research has devoted special attention to the doping of well-known materials (i.e., calcium phosphates and silicates) with bioactive ions, aiming to enhance the osteogenic ability and bioresorbability of man-made grafts. Moreover, high expectations rely on hybrid biopolymer/ceramic materials that mimic the complex composition and multiscale structure of bone tissue.

Technology: general issues --- History of engineering & technology --- biomaterials --- bone grafts --- bone repair --- dental implants --- scaffolds --- alumina --- zirconia --- Alumina-Toughened Zirconia --- Zirconia-Toughened Alumina --- hip arthroplasty --- calcium phosphates --- hydroxyapatite --- bone cements --- bioactive composites --- bone regeneration --- zirconia–alumina composite --- stabilizing oxides --- critical grain size --- tetragonality --- mechanical properties --- fracture toughness --- flexural strength --- ceramic additive manufacturing --- DLP --- bioceramics --- calcium phosphate --- carbon fibers --- mineralization --- zirconia-toughened alumina --- phase transformation --- Raman spectroscopy --- calcium-based biomineralization --- hydroxyapatite nanoparticles --- biomimicry --- multifunctional materials --- Freeze Foam --- hybrid bone --- biocompatibility --- bone replacement --- transformation toughening --- platelet reinforcement --- hip --- alumina matrix composite --- AMC --- hip prosthesis --- prosthesis --- case series --- ceramic-on-ceramic --- n/a --- zirconia-alumina composite