Examinando por Materia "Spectrum Analysis"

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    Deformation behaviour of aged coronal dentin
    (Blackwell Munksgaard, 2018-06-01) Montoya; C.; Arola; D.; Ossa; E.A.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de Ingeniería
    Objective: This study aimed to identify the changes in the time-dependent deformation response of coronal dentin with ageing and its relationship with changes in chemical composition. Background: The structural behaviour of dentin with ageing is affected by changes in the density and diameter of its dentinal tubules (ie porosity), as well as changes in chemical composition throughout the tooth. However, little is known about the time-dependent deformation behaviour of aged dentin and the importance of its hierarchical structure and variations in chemical composition. Materials and methods: The spherical indentation response of aged coronal dentin was analysed in the outer, middle and inner regions, and its time-dependent deformation response was modelled in terms of its microstructure and chemical composition using a model recently proposed for young dentin. Results: The viscous deformation behaviour of aged dentin followed a power-law response with a decrease in the stress exponent when compared to young dentin. These results can be explained by cross-linking of the collagen present in the tissue. Conclusion: A decrease in the deformation ability of aged dentin was found. This behaviour could be a result of a dissolution process and reprecipitation of the minerals present in intertubular dentin into the dentinal tubules. © 2018 John Wiley & Sons A/S and The Gerodontology Association. Published by John Wiley & Sons Ltd
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    The limiting layer of fish scales: Structure and properties
    (ELSEVIER SCI LTD, 2018-02-01) Arola D.; Murcia S.; Stossel M.; Pahuja R.; Linley T.; Devaraj A.; Ramulu M.; Ossa E.A.; Wang J.; Arola D.; Murcia S.; Stossel M.; Pahuja R.; Linley T.; Devaraj A.; Ramulu M.; Ossa E.A.; Wang J.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de Ingeniería
    Fish scales serve as a flexible natural armor that have received increasing attention across the materials community. Most efforts in this area have focused on the composite structure of the predominately organic elasmodine, and limited work addresses the highly mineralized external portion known as the Limiting Layer (LL). This coating serves as the first barrier to external threats and plays an important role in resisting puncture. In this investigation the structure, composition and mechanical behavior of the LL were explored for three different fish, including the arapaima (Arapaima gigas), the tarpon (Megalops atlanticus) and the carp (Cyprinus carpio). The scales of these three fish have received the most attention within the materials community. Features of the LL were evaluated with respect to anatomical position to distinguish site-specific functional differences. Results show that there are significant differences in the surface morphology of the LL from posterior and anterior regions in the scales, and between the three fish species. The calcium to phosphorus ratio and the mineral to collagen ratios of the LL are not equivalent among the three fish. Results from nanoindentation showed that the LL of tarpon scales is the hardest, followed by the carp and the arapaima and the differences in hardness are related to the apatite structure, possibly induced by the growth rate and environment of each fish.STATEMENT OF SIGNIFICANCE: The natural armor of fish, turtles and other animals, has become a topic of substantial scientific interest. The majority of investigations have focused on the more highly organic layer known as the elasmodine. The present study addresses the highly mineralized external portion known as the Limiting Layer (LL). Specifically, the structure, composition and mechanical behavior of the LL were explored for three different fish, including the arapaima (Arapaima gigas), the tarpon (Megalops atlanticus) and the carp (Cyprinus carpio). Results show that there are significant differences in the surface morphology of the LL from posterior and anterior regions in the scales, and between the three species. In addition, the composition of the LL is also unique among the three fish. Results from nanoindentation showed that the LL of tarpon scales is the hardest, followed by the carp and the arapaima and the differences in hardness are related to the apatite structure, possibly induced by the growth rate and environment of each fish. In addition, a new feature was indentified in the LL, which has not been discussed before. As such, we feel this work is unique and makes a significant contribution to the field. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.