Effect of test conditions on instrumental texture parameters of kalakand (original) (raw)
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Biomaterials, 2009
The growth front of nacreous layer, which lies just above the outer prismatic layer, is one of the crucial areas to comprehend the formation of nacreous aragonite. The crystallographic properties of aragonite crystals at the growth front in pearl oyster, Pinctada fucata, were investigated using scanning electron microscopy with electron back-scattered diffraction, and transmission electron microscopy with focused ion beam sample preparation technique. Nano-sized aragonite crystals nucleate with random crystallographic orientation inside the dimples on the surface of the organic matrix that covers the outer prismatic columns. The dimples are filled with horn-like aragonite crystals, which enlarge from the bottom to the upper surface to form hemispheric domes. The domes grow concentrically and coalesce together to become the initial nacreous layer. The c-axes of aragonite at the top surface of the domes are preferentially oriented perpendicular to the surface. The horn-like aragonite and its crystallographic orientation are probably attained by geometrical selection with the fastest growth rate of aragonite along the c-axis, until organic sheets are continuously formed and interrupt the crystal growth of aragonite. The further crystal growth along the shell thickness is attained via mineral bridges through discontinuity or holes in the organic sheets. These results indicate that the crystal growth of aragonite at the growth front results from not only biotic process but also inorganic ones such as geometrical selection and mineral bridges.
Microstructure and Orientation Distribution of Aragonite Crystals in Nacreous Layer of Pearl Shells
MATERIALS TRANSACTIONS, 2004
The microstructure and orientation distribution of aragonite crystals in the nacreous layer of cultured Pteria penguin are investigated in this paper. Helical patterns formed by growth forefronts of the nacreous layer for good-quality shells are observed using a laser microscope, whereas no clear pattern is observed on the nacreous layer surfaces of bad-quality shells. The observed aragonite crystals are plate-shaped and hexagonal for both the good and bad-quality shells, in which the top and bottom faces are parallel to the (001) plane and the side faces are parallel to the {110} and (010) planes. The aragonite crystals in the nacreous layer of good-quality shells seem to be harmonically oriented along a crystallographic direction. These orientation distributions basically indicate that the (001) basal planes are parallel to the inner shell surface, and the [100] and [010] axes are oriented in almost the same direction, respectively. Some of the aragonite crystals are rotated about the c axis by approximately AE60 from the basic orientation distribution. On the other hand, the aragonite crystals of bad-quality shells seem to be randomly oriented in the nacreous layer. These orientation distributions indicate that the (001) basal planes are parallel to the inner shell surface in a similar manner as those of good-quality shells, but their [100] and [010] axes are randomly oriented about the c axis. Therefore, it is considered that such different orientation distributions result in different qualities of pearls that are developed in the shells.
Cahiers De Biologie Marine, 2011
For the purpose of using the nacreous layer of the pearl oyster Pinctada radiata shell in biomedical applications, its mineralogy, microstructure, thermal properties, water and organic matrix content and elemental composition of mineral and organic phases were investigated. P. radiata shell consisted of two mineralized layers: an outer calcitic prismatic layer and an inner aragonitic one exhibiting a "Brick and mortar" micro-architecture. Thermal and elemental analyses revealed that nacre of P. radiata was composed of 4.28% weight (wt) of organic matrix consisting of 1.01% of carbon, 0.49% of hydrogen, 0.39% of nitrogen and 0.08% of sulphur. FTIR analyses showed that the nacreous organic matrix contained functional amine, amide, sulfate and carboxylic acid groups and sugars. The presence of water in nacre was confirmed and measured at 0.34% wt. These results showed that the nacreous layer of P. radiata had comparable microstructure, composition and thermal properties to those of other pearl oysters nacres which exhibited osteogenic and osteoinductive properties. However, its higher organic matrix amount could make it more interesting for biomedical applications considering the significant role of the organic part in the mechanical and osteoinductive properties of a biomedical material.
First characterization report of natural pearl of Pinctada fucata from Gulf of Mannar
Biotechnology Research and Innovation, 2018
The present study is aimed to characterize the natural pearl of Pinctada fucata from Gulf of Mannar by Scanning Electron Microscope (SEM) and Energy Dispersive Studies (EDS). Pearl oysters (P. fucata) from Kayalpattinam, Gulf of Mannar, were landed as a by-catch in the bottom set gill net at a depth of 4 m and collected for tissue culture studies. During mantle tissue dissection, a good lustrous, round pearl of 1.5 mm size was found in the mantle fold of pearl oyster P. fucata. This evidenced the existence of natural pearl oyster beds and natural pearls in this region. It was analyzed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) to find out the composition of nacre. Parallel orientation of crystals to form the lamellar formation of nacre is clearly visible in SEM. Pseudo-hexagonal aragonite crystals arranged in a uniform layer and joined together to form a lamella with inter-lamellar matrix. Two forms of calcium (CaO and CaCO 3) obtained in EDS analysis. Calcium content in the natural pearl is 66.05% which is clearly reveals the aragonite form. Niobium (Nb) was attained at 6% in natural pearl which is the first report in its kind and it may also play a role in the formation of lustrous layer. There are so many characterization reports available about mother of pearl in shell of different species, but this is the first report of natural pearl from P. fucata.
Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 2011
The nacre-prism transition of the mollusc shell Pinctada margaritifera was studied using scanning electron microscopy, electron probe micro-analysis (EPMA) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Mineralogical change is correlated with a change in organic matrix. Previous analyses had shown that sugars were involved in the transition layer (fibrous aragonite). The new Energy Dispersive Spectrometry (EDS) and TOF-SIMS maps show that the modifications at the layer boundary are complex, and that proteins and lipids are also involved. Detailed TOF-SIMS maps show that the thick organic envelopes surrounding the prisms, and between the prisms and the fibrous aragonitic layer, are not composed by regular layers, but are a patchwork of various molecules. The amino acid compositions of the nacreous and prismatic layer are compared thanks to the TOF-SIMS localized analyses.
PloS one, 2013
The initial growth of the nacreous layer is crucial for comprehending the formation of nacreous aragonite. A flat pearl method in the presence of the inner-shell film was conducted to evaluate the role of matrix proteins in the initial stages of nacre biomineralization in vivo. We examined the crystals deposited on a substrate and the expression patterns of the matrix proteins in the mantle facing the substrate. In this study, the aragonite crystals nucleated on the surface at 5 days in the inner-shell film system. In the film-free system, the calcite crystals nucleated at 5 days, a new organic film covered the calcite, and the aragonite nucleated at 10 days. This meant that the nacre lamellae appeared in the inner-shell film system 5 days earlier than that in the film-free system, timing that was consistent with the maximum level of matrix proteins during the first 20 days. In addition, matrix proteins (Nacrein, MSI60, N19, N16 and Pif80) had similar expression patterns in controll...
A modified integrated model of the internal structure of Chinese cultured pearls
Journal of Wuhan University of Technology-materials Science Edition, 2011
Optical and micro-infrared microscope were used to observe the internal structure and mineral composition of high and low quality Chinese seawater and freshwater cultured pearls. Results clearly reveal that aragonite and calcite are found in seawater cultured pearls, but vaterite is not found. In contrast, vaterite and aragonite are found in freshwater cultured pearls, but calcite is not found. Based on our analysis and observations of the internal structure of high and low quality cultured pearls, a modified integrated model of the internal structure of Chinese cultured pearls was established. Our revisions to the previous model focus on significant differences within the prismatic layer of Chinese cultured pearls.
Structural distortion of biogenic aragonite in strongly textured mollusc shell layers
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2010
The stabilisation of strong textures in mollusc shells has for long been a strong drawback towards precise structural determinations of these natural biocomposites. We demonstrate here on several crossed lamellar and nacre layers from two gastropods (Charonia lampas lampas and Haliotis tuberculata tuberculata) and one bivalve (Pinctada maxima), that on real specimens (without grinding or specific preparation), the textural information can be used efficiently for precise structural determination of the biogenic aragonite. This is done through the combination of orientation distribution function and cyclic Rietveld refinements on several hundreds to thousands of diffractions diagrams.
Analytical and Bioanalytical Chemistry, 2008
A microstructural, mineralogical, and chemical study of the nacre-prisms boundary in the shells of Pinctada margaritifera shows that this boundary is not an abrupt transition, but that there exists a distinct fibrous layer with clear topographic structures and evidence of growth lines. A three-step biomineralization process is proposed that involves changes in the chemical and biochemical composition of the last growth increments of the calcite prisms, formation of the fibrous layer, and development of regular tablets in the nacreous layer.