Correlation between Microstructure and Failure Mechanism of Hyriopsis cumingii Shell Structure

The structure of pristine preserved shells of Mesozoic ammonoids was examined in order to identify whether there are homologous or homoplasic traits in the internal structure of the shell wall that can be used for phylogeny and taxonomy, particularly in regard to episodic growth interruptions and the dorsal shell wall. Different sculptural elements that are usually associated with an interruption in shell growth, like varices, constrictions, flares, parabolae and radial lirae, were analysed to determine whether these have a general ground plan in internal structure or not. Varices and constrictions shows no interruptions in shell growth but have characteristic internal thickenings formed by the nacreous layer. Owing to the general structural conformity of varices and constrictions in the shells of Jurassic and Cretaceous taxa, they are probably homologous traits. Flares, parabolae and radial lirae are characterized by an interruption in growth, they mark the succession of two different shell generations. Parabolae and flares mark an interruption of shell growth caused by the formation of a frill-like, outwardly bent temporary aperture (but differ in their general shape). The outer prismatic layer, the nacreous layer and an apertural prismatic coating (i.e. indicates a mantle cover) build their aperture. Radial lirae are formed by imbrication of two successive sigmoid shell lamellae, formed either by the organic periostracum or the outer prismatic layer. Each lira has a characteristic adorally-projecting, scythe-like appendage arising from its crest. Owing to the general structural and morphological conformity of flares and parabolae it is likely that both represent different expressions of a homologous structure. Morphological transitions imply that parabolae and radial lirae are probably homologous as well. Mesozoic Ammonoidea had different types of the dorsal shell wall. The vast majority of planispirally taxa forms a prismatic reduced dorsal shell wall, consisting of an outer organic component (e.g. wrinkle layer) and the subsequent formed dorsal inner prismatic layer. The latter is only secreted in the rear of the living chamber. Reduced dorsal shell wall construction of Ammonoidea is generally homologous and exists in the early ontogenetic stages of all taxa. Rather few ammonoid taxa reinforce the dorsal shell wall. Some planispirally taxa form a nacreous reduced dorsal shell wall in the rear part of the living chamber, which is reinforced by secondary pair of nacreous and inner prismatic layers. Heteromorph taxa and some planispirally taxa secreted a complete dorsal shell wall at the aperture, i.e. the ventral, lateral and dorsal shell wall form a continum aperturally and adapically. The dorsal shell layers are identical with the ventral shell wall. The broad phylogenetic distribution of dorsally secreted nacre indicates a plesiomorphic relic trait of the orthocone ammonoid ancestors.

Nanoscale structural and mechanical characterization of the shell of a red abalone has been carried out. Cobble-like polygonal nanograins are basic building blocks that are used to construct individual aragonite platelets into a mother-of-pearl configuration known as nacre. The nanograin-structured aragonite platelets are not brittle in nature, but somewhat ductile. The deformability of the aragonite platelets together with the crack deflection, aragonite platelet slip, and organic adhesive interlayer contribute to the nacre's fracture toughness. Cracks formed in the outer prismatic layer of the shell do not show the crack diversion mechanism.

BackgroundDespite its economic importance, we have a limited understanding of the molecular mechanisms underlying shell formation in pearl oysters, wherein the calcium carbonate crystals, nacre and prism, are formed in a highly controlled manner. We constructed comprehensive expressed gene profiles in the shell-forming tissues of the pearl oyster Pinctada fucata and identified novel shell formation-related genes candidates.Principal FindingsWe employed the GS FLX 454 system and constructed transcriptome data sets from pallial mantle and pearl sac, which form the nacreous layer, and from the mantle edge, which forms the prismatic layer in P. fucata. We sequenced 260477 reads and obtained 29682 unique sequences. We also screened novel nacreous and prismatic gene candidates by a combined analysis of sequence and expression data sets, and identified various genes encoding lectin, protease, protease inhibitors, lysine-rich matrix protein, and secreting calcium-binding proteins. We also examined the expression of known nacreous and prismatic genes in our EST library and identified novel isoforms with tissue-specific expressions.ConclusionsWe constructed EST data sets from the nacre- and prism-producing tissues in P. fucata and found 29682 unique sequences containing novel gene candidates for nacreous and prismatic layer formation. This is the first report of deep sequencing of ESTs in the shell-forming tissues of P. fucata and our data provide a powerful tool for a comprehensive understanding of the molecular mechanisms of molluscan biomineralization.

Carbonate biological hard tissues are valuable archives of environmental information. However, this information can be blurred or even completely lost as hard tissues undergo diagenetic alteration. This is more likely to occur in aragonitic skeletons because bioaragonite commonly transforms into calcite during diagenesis. For reliably using aragonitic skeletons as geochemical proxies, it is necessary to understand in depth the diagenetic alteration processes that they undergo. Several works have recently investigated the hydrothermal alteration of aragonitic hard tissues during short term experiments at high temperatures (T > 160 °C). In this study, we conduct long term (4 and 6 months) hydrothermal alteration experiments at 80 °C using burial-like fluids. We document and evaluate the changes undergone by the outer and inner layers of Arctica islandica shell, the prismatic and nacreous layers of Haliotis ovina shell, and the skeleton of Porites sp. combining a variety of analytical tools (X-ray diffraction, thermogravimetry analysis, laser confocal microscopy, scanning electron microscopy, electron backscatter diffraction and atomic force microscopy). We demonstrate that this approach is the most adequate to trace subtle, diagenetic alteration-related changes in aragonitic biocarbonates. Furthermore, we unveil that the diagenetic alteration of aragonitic hard tissues is a complex multi-step process where major changes occur even at the low temperature used in this study and well before any aragonite into calcite transformation takes place. Alteration starts with biopolymer decomposition and concomitant generation of secondary porosity. These processes are followed by abiogenic aragonite precipitation that partially or totally obliterates the secondary porosity. Only afterwards any transformation of aragonite into calcite takes place. The kinetics of the alteration is highly dependent on primary microstructural features of the aragonitic biomineral. While the skeleton of Porites sp. remains virtually unaltered within the time spam of the experiments, Haliotis ovina nacre undergoes extensive abiogenic aragonite precipitation, the outer and inner layers of Arctica islandica shell are significantly affected by aragonite transformation into calcite and this transformations extensive in the case of the prismatic layer of Haliotis ovina shell. Our results suggest that most aragonitic fossil archives may be overprinted, even those free of clear diagenetic alteration signs. This finding may have major implications for the use of these archives as geochemical proxies.

Comprehensive biochemistry. Volume 11: Water-soluble vitamins, hormones, and antibiotics: Edited by Marcel Florkin and Elmer H. Stotz. Elsevier, Amsterdam (1963). xvi + 237 pp. $11.50

The shell of the Japanese pearl oyster, Pinctada fucata, consists of two layers, the prismatic layer on the outside and the nacreous layer on the inside, both of which comprise calcium carbonate and organic matrices. Previous studies indicate that the nacreous organic matrix of the central layer of the framework surrounding the aragonite tablet is beta-chitin, but it remains unknown whether organic matrices in the prismatic layer contain chitin or not. In the present study, we identified chitin in the prismatic layer of the Japanese pearl oyster, Pinctada fucata, with a combination of Calcofluor White staining with IR and NMR spectral analyses. Furthermore, we cloned a cDNA encoding chitin synthase (PfCHS1) that produces chitin, contributing to the formation of the framework for calcification in the shell.

Nacre is a classic model, providing an inspiration for fabricating high‐performance bulk nanocomposites with the two‐dimensional platelets. However, the “brick” of nacre, aragonite platelet, is an ideal building block for making high‐performance bulk nanocomposites. Herein, we demonstrated a strong and tough conductive nacre through reassembling aragonite platelets with bridged by MXene nanosheets and hydrogen bonding, not only providing high mechanical properties but also excellent electrical conductivity. The flexural strength and fracture toughness of the obtained conductive nacre reach ~282 MPa and ~6.3 MPa m1/2, which is 1.6 and 1.6 times higher than that of natural nacre, respectively. These properties are attributed to densification and high orientation degree of the conductive nacre, which is effectively induced by the combined interactions of hydrogen bonding and MXene nanosheets bridging. The crack propagations in conductive nacre are effectively inhibited through crack deflection with hydrogen bonding, and MXene nanosheets bridging between aragonite platelets. In addition, our conductive nacre also provides a self‐monitoring function for structural damage and offers exceptional electromagnetic interference shielding performance. Our strategy of reassembling the aragonite platelets exfoliated from waste nacre into high‐performance artificial nacre, provides an avenue for fabricating high‐performance bulk nanocomposites through the sustainable reutilization of shell resources.

Effects of ultrasound on invasive golden mussel Limnoperna fortunei mortality and tissue lesions

Mollusk shells represent important archives for paleoclimatic studies aiming to reconstruct environmental conditions at high temporal resolution. However, the shells, made of calcium carbonate in the form of aragonite and /or calcite, can be altered through time which may undermine the suitability for any reconstruction based on geochemical proxies (i.e., stable isotopes, radiocarbon). At present, the diagenetic processes involved in this chemical and physical deterioration are still poorly understood. The present study aims to shed light on the onset and development of diagenetic alteration in the aragonitic shell of Phorcus turbinatus. To artificially mimic diagenesis, shells of P. turbinatus were exposed to elevated temperatures. The transformation of the mineral phase was monitored by means of Confocal Raman Microscopy whereas the structural changes were investigated using Scanning Electron Microscopy and Atomic Force Microscopy. The results indicate that the two distinct shell layers (prismatic layer and nacre) respond differently to the elevated temperatures, suggesting that the different microstructural organization and organic content may drive the onset and spread of the aragonite-to-calcite transformation. Furthermore, changes in the microstructural arrangement became visible prior to the mineralogical transition. Our results demonstrate that the specific physico-chemical characteristics of structurally different areas within the biogenic carbonates have to be taken into account when studying the phase transformation occurring during diagenesis.

This research is about manufacturing brake pads from a polymeric composite material composed of domestic materials, which are cheaper and available in the market. An unsaturated polyester is used as the basic material. Styrene–butadiene rubber and montmorillonite clay materials available in the market are used as the fillers. The Kevlar fibers, the nylon, and the steel fibers are used as reinforcing materials to improve the mechanical properties. The Shore hardness, compressibility, thermal conductivity, impact, and wear resistance tests have been implemented. The results show that the hardness, compressive, and impact resistance of the samples increase with the increase of the reinforcement ratio by Kevlar fibers, nylon fibers, and steel fibers. The rate of wear decreases with the increase of reinforcement ratio. The thermal conductivity decreases with an increase in the reinforcement ratio by Kevlar fibers and nylon fibers while the thermal conductivity increases with an increase in the reinforcement ratio by Kevlar fibers and steel fibers. Compared to the commercial brake pads, high strength, high wear resistance, high impact resistance, high hardness, high compressive strength, low thermal conductivity, and low-cost brake pads have been proposed.

Static and impact performance of engineered cementitious composites with hybrid graphite nano platelets modified PVA and shape memory alloy fibres

Hyriopsis cumingii is an economically important freshwater pearl mussel with high pearl quality that is endemic in China. Investigation of genes relevant to shell formation is important for increased pearl output. The substances that form mollusk shells are secreted by epithelial cells in the mantle, the proliferation of which influences secretion ability. This study focused on the proliferation-related 37-kDa laminin receptor precursor (37LRP) of H. cumingii. The full-length cDNA (1133 bp) encoding this 300-amino acid protein was cloned from the mantle. Quantitative fluorescence analysis showed that 37LRP expressed in eight tissues, with the highest expression observed in the liver, and its expression pattern in the mantle reflected shell repair. During repair, 37LRP expression was higher in the experimental shell repair group than that in the control group, exhibiting an initial increase followed by a decrease in expression, and returning to basal levels on completion of the repair. A similar trend was also observed with respect to immunity and cellular metabolism. Expression of the 37LRP protein in the experimental group was significantly higher than that in the control group at the first and second days after shell injury. After 4 days, 37LRP expression in the experimental group was lower than that in the control group. In situ hybridization revealed a strong positive signal corresponding to the 37LRP mRNA at the horny grooves of the mantle, evagination, and in epithelial cells of the velum, which implicated these areas in the repair and formation of the cuticle, prismatic layer, and nacre.

Background and Aims The classification of renal diseases is dependent on the evaluation of kidney biopsies using light microscopy techniques. Ultrastructural details (e.g. podocyte foot processes, amyloid fibrils, Fabri's intracellular inclusions) need transmission electron microscopy (TEM) which has high costs, requires specialized personnel and is time consuming. Therefore, alternative techniques are highly desirable. Here we report our experience with scanning electron microscopy (SEM) and atomic force microscopy (AFM). Method Paraffin-embedded kidney sections (3μm thick) were examined after dewaxing and Jones-methenamine methane staining for type IV collagen fibers. Dried urine sediments were prepared using standard methods for urine cytological analysis. Analysis was then performed using atomic force microscopy (nGauge system) on dried specimens and with Scanning Electron Microscopy (Zeiss) after gold-spattering of the surface. Reference images were obtained by standard microscopy. Results The combination of SEM and thin paraffin sections allows the observation of ultrastructural details in kidney biopsies with a very simple and fast preparation. AFM is even faster than SEM, as it does not require any preparation of the surface of the sample. An important advantage of SEM is the possibility to view the sample at low magnification, which makes it easier to identify the location of the glomeruli. It is thus possible to switch from small magnifications (100x) to very extreme magnifications (10000x). Notably, the interpretation of the images requires knowledge of the artifacts induced by paraffin inclusion. Specifically, structures and cells containing lipids (for example foamy cells) appear empty. Chromatin is also condensed in the nuclei around the periphery of the nucleus and in spike structures whit large empty areas. The recognition of nuclei in SEM and AFM is important for the subsequent interpretation of the images. Podocyte pedicles fusion can be identified relatively easily in SEM and in AFM. Both techniques add relevant ultrastructural details of urine sediment cells, from epithelial cells to isolated tubular cells. Also, casts show many ultrastructural features which are not evident in classical optical microscopy. It is also possible to measure the thickness of the basement membrane with great precision both in SEM and with AFM. The major limitation of this approach is the limited experience of pathologists with these methods and the absence of an atlas of normal and pathological kidney. Conclusion Considering the affordable costs of SEM and AFM instruments and the simple preparation of samples for their analysis, these should be considered a valid alternative to TEM. SEM and AFM are alternative methods, simple and relatively cheap and very fast to obtain ultrastructural details of renal biopsies. We thank ANED and AST for the great support given to research.

The influence of bagasse fibres from beer manufacturing in mechanical, thermal, and rheological properties of three polymers (BioPE, PLA, and PP) has been studied in order to develop new environmentally friendly biocomposites for injection moulding applications. Totals of 10 wt%, 20 wt%, and 30 wt% of bagasse fibre (BSG) were added to the polymers by extrusion compounding, adding specific compatibilising additives, and injected samples were mechanically characterised by tensile, Charpy impact, and hardness tests. In addition, the fractures obtained after the impact test were observed using scanning electron microscopy (SEM) to assess the compatibility matrix filler. Characterisation of the thermal properties is also carried out by using differential scanning calorimetry (DSC) and thermogravimetry (TGA). Additionally, melt flow index of the biocomposites is also studied. An increase in the rigidity of the BioPE and PP composites was produced with the increase in BSG content, dealing with a decrease in maximum strain and impact resistance; whereas, in the filled BGS PLA biocomposites, Young's modulus was lower than that of the PLA material, improving the ductility of the PLA-BGS formulations. Compatibilisation effect was, therefore, different in the nine developed formulations, and the BGS content also influenced their thermal, mechanical, and rheological behaviours.

More than 40 years after its invention, the atomic force microscopy (AFM) can be integrated with scanning electron microscope (SEM) instruments as an increasingly capable and productive characterization tool with sub-nanometer spatial resolution. The authors have designed and developed an AFM instrument capable to be integrated into any SEM or in a combination of SEM with a focused ion-beam (FIB) tool. The combination of two or more different types of techniques like SEM, energy dispersive x-ray spectroscopy, and AFM is called correlative microscopy because analytical information from the same place of the sample can be obtained and correlated. For the first time, they introduced to the SEM/FIB tool correlative nanofabrication methods like field-emission scanning probe lithography, tip-based electron beam induced deposition, and nanomachining. The combination of all these methods provides a completely new nanotechnology instrument, which should be seen as a tool for correlative nanofabrication and microscopy. Thus, it provides for the first time the capabilities of a stand-alone instrument with the capabilities of nondestructive three-dimensional tip-based metrology and nanofabrication into the combined SEM/FIB tool. In this article, the authors describe all these methods in detail and present a brief example of the results obtained. They demonstrate that the self-sensing, self-actuating cantilevers (called active cantilevers) equipped with Diamond tip are a versatile toolkit for fast imaging and emerging nanofabrication. The AFM integrated into SEM is using active cantilevers that can characterize and generate nanostructures all in situ without the need to break-vacuum or contaminate the sample.