Nacreous Layer Research Articles

Nacre-Inspired Nanocomposites from Natural Polypeptide ε-Poly-l-Lysine and Natural Clay Montmorillonite: Remarkable Reinforcing Effect at Low Polymer Content and Its Mechanism.

Nanocomposites composed of the cationic polypeptide ε-poly-l-lysine (ε-PL) and natural sodium montmorillonite (MMT) were prepared and evaluated. These MMT/ε-PL composites formed highly ordered nanostructures resembling natural nacreous layers by a simple process. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses confirmed that a small amount of ε-PL remarkably enhanced the MMT orientation in the composites. This MMT orientation-enhancing effect of ε-PL was more pronounced than that of poly(vinyl alcohol) (PVA), which is one of the most popular ingredients of MMT-based composites. The orientation enhancement provided by ε-PL was primarily driven by ionic interactions and responsible for high mechanical properties at low polymer content. This remarkable reinforcing effect of ε-PL on MMT at a low polymer content will help to develop high-performance and sustainable nacreous composites. In addition, it improves our understanding of the reinforcing mechanism of natural nacre, which exhibits excellent mechanical properties even with relatively small amounts of organic component.

Ballistic properties of bioinspired nacre-like ceramic/polyurea staggered composite structures

We proposed a bioinspired ceramic/polyurea composite plate that draws on a “brick-mortar” arrangement of nacre layer, with a periodic three-dimensional structure and interlayers polyurea elastomers. We fired a 12.7 mm armor-piercing incendiary bullet using a ballistic gun to conduct depth-of-penetration (DOP) experiments. We analyzed the damage, fracture morphology, and residual DOP of ceramic/polyurea-staggered composite structures (CPSCS), with a theoretical prediction model for the residual DOP. Using the adaptive FEM-SPH algorithm, we compared the damage morphology of CPSCSs. We analyzed projectile penetration process and summarized four toughening modes using stress wave propagation. Based on simulation fitting and theoretical calculations, we obtained the residual DOP curves at different projectile velocities and analyzed the toughening effect of the CPSCSs through the energy dissipation of each structural component. When the areal density was the same, the residual DOP of the CPSCSs decreased by 33.9 %, and the critical velocity theoretically increased by 32.72 %. The error between the model calculations and experimental results was 11 %. The CPSCSs enabled the ceramic to increase the energy absorption efficiency by 179.70 %. With the same structural form, changing the thickness of only one component did not have the same effect on the structural energy-absorption efficiency as changing the entire form.

Significance of microstructural defect-tolerant in the battle for survival: Mantis shrimp VS. Nacre

Mantis shrimps use their robust claws to repeatedly strike and break the shells of bivalves during predation without sustaining damage themselves. It appears to be a confrontation between the bouligand microstructure and the brick-and-mortar microstructure of the nacre layer. In the daily struggle for survival, defects are inevitably introduced. To elucidate the mechanical mechanisms exhibited by the two microstructures in the struggle for survival, thus a bold conjecture was proposed: the bouligand structure exhibits less sensitivity to random defects compared to the brick-and-mortar structure, enabling mantis shrimps to survive in the battle for existence. To verify this hypothesis, numerical models of bouligand and brick-and-mortar microstructures were established considering interfacial random defects. The results indicated that for various defect volume fraction, the bouligand structure demonstrates superior mechanical performance compared to the brick-and-mortar structure. In terms of peak load and damage dissipation energy, the bouligand structure exhibits higher tolerance to interfacial random defects than the brick-and-mortar structure, delaying the occurrence of damage in the Bouligand structure while prematurely inducing damage in the brick-and-mortar structure. This study not only reveals the mechanical mechanisms behind the advantages of biological microstructures in the struggle for survival but also provides technical references for future biomimetic microstructure designs.

Research progress on formation mechanism of pearl

Pearls are deeply cherished for their rich color and gorgeous luster, and their quality directly affects their value. Currently, the evaluation of pearl quality is mainly based on four aspects: color, shape, size and smoothness. The quality of pearls is influenced by a variety of factors, categorized into internal factors, such as the structural composition of the nacreous layer and genetic factors of the mussels, and external factors, including the aquaculture environment. Existing research results indicates that genetic factors are the dominant factor controlling the pearl quality. However, the macromolecules such as metal ions, organic pigments and various physical and chemical factors in the aquaculture water environment will also significantly impact pearl quality. Among these, matrix proteins are organic macromolecules found in the nacreous layer that play an important role in pearl quality. They participate in the deposition of calcium carbonate and the construction of the organic framework, affecting the pearls’ size and shape. The color of pearls is influenced by the deposition of metal ions, the transport of organic pigments and the regulation of microstructure.

HcN57, A Novel Unusual Acidic Silk-Like Matrix Protein from Hyriopsis cumingii, Participates in Framework Construction and Nacre Nucleation During Nacreous Layer Formation.

In the classic molecular model of nacreous layer formation, unusual acidic matrix proteins rich in aspartic acid (Asp) residues are essential for nacre nucleation due to their great affinity for binding calcium. However, the acidic matrix proteins discovered in the nacreous layer so far have been weakly acidic with a high proportion of glutamate. In the present study, several silk-like matrix proteins, including the novel matrix protein HcN57, were identified in the ethylenediaminetetraacetic acid-soluble extracts of the nacreous layer of Hyriopsis cumingii. HcN57 is a highly repetitive protein that consists of a high proportion of alanine (Ala, 34.4%), glycine (Gly, 22.5%), and serine (Ser, 11.4%). It forms poly Ala blocks, GlynX repeats, an Ala-Gly repeat, and a Ser-Ala-rich region, exhibiting significant similarity to silk proteins found in spider species. The expression of HcN57 was specifically located in the dorsal epithelial cells of the mantle pallium and mantle center. Notably, expression of HcN57 was relatively high during nacreous layer regeneration and pearl nacre deposition, suggesting HcN57 is a silk matrix protein in the nacreous layer. Importantly, HcN57 also contains a certain content of Asp residues, making it an unusual acidic matrix protein present in the nacreous layer. These Asp residues are mainly distributed in three large hydrophilic acidic regions, which showed inhibitory activity against aragonite deposition and morphological regulation of calcite in vitro. Moreover, HcN57-dsRNA injection resulted in failure of nacre nucleation in vivo. Taken together, our results show that HcN57 is a bifunctional silk protein with poly Ala blocks and Gly-rich regions that serve as space fillers within the chitinous framework to prevent crystallization at unnecessary nucleation sites and Asp-rich regions that create a calcium ion supersaturated microenvironment for nucleation in the center of nacre tablets. These observations contribute to a better understanding of the mechanism by which silk proteins regulate framework construction and nacre nucleation during nacreous layer formation.

Diversification of von Willebrand Factor A and Chitin-Binding Domains in Pif/BMSPs Among Mollusks

Pif is a shell matrix protein (SMP) identified in the nacreous layer of Pinctada fucata (Pfu) comprised two proteins, Pif97 and Pif 80. Pif97 contains a von Willebrand factor A (VWA) and chitin-binding domains, whereas Pif80 can bind calcium carbonate crystals. The VWA domain is conserved in the SMPs of various mollusk species; however, their phylogenetic relationship remains obscure. Furthermore, although the VWA domain participates in protein–protein interactions, its role in shell formation has not been established. Accordingly, in the current study, we investigate the phylogenetic relationship between PfuPif and other VWA domain-containing proteins in major mollusk species. The shell-related proteins containing VWA domains formed a large clade (the Pif/BMSP family) and were classified into eight subfamilies with unique sequential features, expression patterns, and taxa diversity. Furthermore, a pull-down assay using recombinant proteins containing the VWA domain of PfuPif 97 revealed that the VWA domain interacts with five nacreous layer-related SMPs of P. fucata, including Pif 80 and nacrein. Collectively, these results suggest that the VWA domain is important in the formation of organic complexes and participates in shell mineralisation.

Advancing responsible genomic analyses of ancient mollusc shells.

The analysis of the DNA entrapped in ancient shells of molluscs has the potential to shed light on the evolution and ecology of this very diverse phylum. Ancient genomics could help reconstruct the responses of molluscs to past climate change, pollution, and human subsistence practices at unprecedented temporal resolutions. Applications are however still in their infancy, partly due to our limited knowledge of DNA preservation in calcium carbonate shells and the need for optimized methods for responsible genomic data generation. To improve ancient shell genomic analyses, we applied high-throughput DNA sequencing to 27 Mytilus mussel shells dated to ~111-6500 years Before Present, and investigated the impact, on DNA recovery, of shell imaging, DNA extraction protocols and shell sub-sampling strategies. First, we detected no quantitative or qualitative deleterious effect of micro-computed tomography for recording shell 3D morphological information prior to sub-sampling. Then, we showed that double-digestion and bleach treatment of shell powder prior to silica-based DNA extraction improves shell DNA recovery, also suggesting that DNA is protected in preservation niches within ancient shells. Finally, all layers that compose Mytilus shells, i.e., the nacreous (aragonite) and prismatic (calcite) carbonate layers, with or without the outer organic layer (periostracum) proved to be valuable DNA reservoirs, with aragonite appearing as the best substrate for genomic analyses. Our work contributes to the understanding of long-term molecular preservation in biominerals and we anticipate that resulting recommendations will be helpful for future efficient and responsible genomic analyses of ancient mollusc shells.

The physiological responses to titanium dioxide nanoparticles exposure in pearl oysters (Pinctada fucata martensii)

To evaluate the physiological responses to titanium dioxide nanoparticles exposure in pearl oysters (Pinctada fucata martensii), pearl oysters were exposed for 14 days to different levels (0.05, 0.5, and 5 mg/L) of nano-TiO2 suspensions, while a control group did not undergo any nano-TiO2 treatment. And then recovery experiments were performed for 7 days without nano-TiO2 exposure. At days 1, 3, 7, 14, 17, and 21, hepatopancreatic tissue samples were collected and used to examine the activities of protease, amylase, lipase, catalase (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD), lysozyme (LYS), alkaline phosphatase (AKP), and acid phosphatase (ACP). The microstructure of the nacreous layer in shell was also analyzed by scanning electron microscopy. Results showed that pearl oysters exposed to 5 mg/L of TiO2 nanoparticles had significantly lower protease, amylase, and lipase activities and significantly higher CAT, SOD, GPx, LYS, ACP, and AKP activities than control pearl oysters did even after 7-day recovery (P-values <0.05). Pearl oysters exposed to 0.5 mg/L or 0.05 mg/L of TiO2 nanoparticles had lower protease, amylase, and lipase activities and higher CAT, SOD, GPx, LYS, ACP, and AKP activities than control pearl oysters did during the exposure period. After 7-day recovery, no significant differences in protease, lipase, SOD, GPx, CAT, ACP, AKP, or LYS activities were observed between pearl oysters exposed to 0.05 mg/L of TiO2 nanoparticles and control pearl oysters (P-values >0.05). In the period from day 7 to day 14, indistinct and irregular nacreous layer crystal structure in shell was observed. This study demonstrates that TiO2 nanoparticles exposure influences the levels of digestion, immune function, oxidative stress, and biomineralization in pearl oysters, which can be partially and weakly alleviated by short-term recovery. These findings contribute to understanding the mechanisms of action of TiO2 nanoparticles in bivalves. However, studies should evaluate whether a longer recovery period can restore to their normal levels in the future.

Investigations on compression behavior of fused filament fabricated hybrid biomimetic structures

The objective of this study is to design a biomimetic hybrid structure inspired by nacre, and conch shells and compare how the compressive characteristics change when key geometric design parameters are varied. Nacre, also known as mother of pearl, has a host of traits, suitable for survival, like its stiffness and strength. Conch, which is a common name for a number of sea snails, possesses a unique cross-lamellar structure which has a tough outer layer to resist penetration from the sharp-toothed attacks of predators, and a nacreous inner layer which can dissipate energy. A novel nacre–conch–nacre inspired sandwich core structure is designed and fabricated with fuse filament fabrication using acrylonitrile styrene acrylate filament according to the ASTM C365 standard for the flatwise compression test of sandwich core structures. Three key design parameters, namely the wall thickness, the thickness between two nacre walls, and the angle of conch were selected and varied to form nine different iterations of this design. An Abaqus finite element analysis was validated by experimental testing using an Instron 8801 servo-hydraulic universal testing machine. The results showed that conch-inspired structures’ compression properties depend on wall thickness and angle. The sample with 2 mm wall thickness and 45° conch angle had the highest compressive strength of 3.62 MPa, while the sample with 1 mm wall thickness and 50° conch angle had the lowest at 2.09 MPa. These findings suggest this structure could be used in lightweight armor, car, and aerospace parts.

Expression of bone morphogenetic protein 10 and its role in biomineralization in Hyriopsis cumingii

Shells and pearls are the products of biomineralization of shellfish after ingesting external mineral ions. Bone morphogenetic proteins (BMPs) play a role in a variety of biological function, and the genes that encode them, are considered important shell-forming genes in mollusks and are associated with shell and pearl formation, embryonic development, and other functions, but bone morphogenetic protein 10 (BMP10) is poorly understood in Hyriopsis cumingii. In this study, we cloned Hc-BMP10 and obtained a 2477 bp full-length sequence encoding 460 amino acids with a conserved TGF-β structural domain. During the embryonic developmental stages, the cleavage stage had the highest expression of Hc-BMP10, followed by juvenile clams; the expression in the mantle gradually decreased with increasing mussel age. A strong signal was detected on epidermal cells on the mantle edge by in situ hybridization. In both the shell notching and inserting operations of the pearl fragment assay, we found that the expression of Hc-BMP10 increased after the above treatments. RNA interference assays showed that the silencing of Hc-BMP10 resulted in a change in the morphology of the prismatic layer and nacreous layer, with the prismatic layer less closely aligned and the disordered aragonite flakes in the nacreous layer. These findings indicate that Hc-BMP10 is involved in the growth and development of H. cumingii, as well as the formation of shells and pearls. Therefore, this study provides some reference for selecting superior species for growth and pearl breeding of H. cumingii at a molecular level and further investigation of the molecular mechanism for biomineralization of Hc-BMP10.

Investigating the potential of African land snail shells (Gastropoda: Achatininae) for amino acid geochronology

Aragonitic calcium carbonate (CaCO3) terrestrial mollusc shells with complex shell microstructures, such as those in the African subfamily Achatininae, have the potential to be used to build amino acid geochronologies across the African continent. However, as different microstructural shell layers are likely to have different protein compositions, sampling strategies need to be developed to identify the most appropriate shell portion to target. To test possible variability in protein degradation rates between microstructural layers, sampling of a single microstructural shell layer (the ‘nacreous’ layer) was compared to sampling all three aragonitic layers ('3AL') in modern and fossil shells. Reliable isolation of the nacreous layer in all samples proved impractical, and additional complications arose due to mineral diagenesis induced by sampling with a drill. Pleistocene fossils of Lissachatina sp. and modern specimens of Achatina tavaresiana Morelet, 1866 were shown to have an intra-crystalline protein fraction. The 3AL shell portion adhered more closely to closed-system behaviour in heated modern, and fossil, samples. The intra-crystalline protein degradation (IcPD) patterns of Achatininae fossil samples were not consistent with IcPD under forced degradation experiments at high temperatures in the laboratory. However, reliable degradation trends were observed in the 3AL shell portion, demonstrating the potential of fossil achatinids for building relative amino acid geochronologies across Africa.

Development of bioinspired damage-tolerant calcium phosphate bulk materials

ABSTRACT Improving the damage tolerance and reliability of ceramic artificial bone materials, such as sintered bodies of hydroxyapatite (HAp), that remain in vivo for long periods of time is of utmost importance. However, the intrinsic brittleness and low damage tolerance of ceramics make this challenging. This paper reports the synthesis of highly damage tolerant calcium phosphate-based materials with a bioinspired design for novel artificial bones. The heat treatment of isophthalate ion-containing octacalcium phosphate compacts in a nitrogen atmosphere at 1000°C for 24 h produced an HAp/β-tricalcium phosphate/pyrolytic carbon composite with a brick-and-mortar structure (similar to that of the nacreous layer). This composite exhibited excellent damage tolerance, with no brittle fracture upon nailing, likely attributable to the specific mechanical properties derived from its unique microstructure. Its maximum bending stress, maximum bending strain, Young’s modulus, and Vickers hardness were 11.7 MPa, 2.8 × 10‒ 2, 5.3 GPa, and 11.7 kgf/mm2, respectively. The material exhibited a lower Young’s modulus and higher fracture strain than that of HAp-sintered bodies and sintered-body samples prepared from pure octacalcium phosphate compacts. Additionally, the apatite-forming ability of the obtained material was confirmed in vitro, using a simulated body fluid. The proposed bioinspired material design could enable the fabrication of highly damage tolerant artificial bones that remain in vivo for long durations of time.

Mineral-free biomaterials from mussel (Mytilus edulis L.) shells: Their isolation and physicochemical properties

One of the modern directions of mussel shells utilisation is associated with the production of mineral-free biomaterials that can be successfully used in food production, feed additives production, in biotechnologies, as well as in biomedicine. The objectives of this study are to obtain an organic matrix (conchix) from mussel (Mytilus edulis L.) shells by demineralisation using two decalcifying agents—a solution of hydrochloric acid (HCl) and a solution of disodium salt of ethylenediaminetetraacetic acid (Na2-EDTA), as well as the influence of the decalcifying agent nature on the organic matrix structure. The degree of demineralisation of the obtained conchixes when using HCl reaches 100%. It has been shown that the native structure of the organic matrix proteins is partially destroyed during the demineralisation of the shells in the HCl solution; analysis of IR spectra indicates a 1.5-fold decrease in the number of α-helices compared to the organic matrix obtained by gentle Na2-EDTA-based demineralisation. SEM and TEM studies indicate the destruction of the biopolymer structure of the outer (periostracum) and inner (prismatic and nacreous) layers of the organic matrix obtained using HCl, while this structure is completely preserved when using Na2-EDTA. The results obtained indicate the preference of using Na2-EDTA for the production of biomaterials with potential use in food technology and biomedicine.

The regulatory effect of NF-κB signaling pathway on biomineralization and shell regeneration in pearl oyster, Pinctada fucata

Pinctada fucata is an important pearl production shellfish in aquaculture. The formation of shells and pearls is a hot research topic in biomineralization, and matrix proteins secreted by the mantle tissues play the key role in this process. However, upstream regulatory mechanisms of transcription factors on the matrix protein genes remain unclear. Previous studies have shown that NF-κB signaling pathway regulated biomineralization process through expression regulation of specific matrix proteins, including Nacrein, Prismalin-14 and MSI60. In this study, we systematically investigated the regulatory effect of the NF-κB signaling pathway key factor Pf-Rel and inhibitory protein poI-κB on the biomineralization and shell regeneration process. We applied RNA interference and antibody injection assays to study in vivo function of transcription factor Pf-Rel and characterized shell morphology changes using scanning electron microscopy and Raman spectroscopy. We found that transcription factor Pf-Rel plays a positive regulatory role in the growth regulation of the prismatic and nacreous layers, while the function of inhibitory protein poI-κB is to prevent excessive growth and accumulation of both layers. RNA-seq was conducted based on RNA interference animal model to identify potential regulatory genes by transcription factor Pf-Rel. Shell damage repair experiments were performed to simulate shell regeneration process, and observations of newly formed shells revealed that NF-κB signaling pathway had different functions at different times. This study provides us with a more macroscopic perspective based on transcription factors to investigate biomineralization and shell regeneration.

AN INSIGHT INTO THE SYSTEMATICS OF PLICATOSTYLIDAE (BIVALVIA), WITH A DESCRIPTION OF &lt;em&gt;PACHYGERVILLIA ANGUILLAENSIS&lt;/em&gt; N. GEN. N. SP. FROM THE &lt;em&gt;LITHIOTIS&lt;/em&gt; FACIES (LOWER JURASSIC) OF ITALY

The Lithiotis facies represents an Early Jurassic global bioevent characterized by a remarkable spread of gregarious bivalves, which produced large sedimentary bodies in tropical shallow-water marine environments. The most peculiar and common genera Lithiotis, Cochlearites and Lithioperna, with aberrant and extremely elongated or strongly flattened shells, have been studied since the second half of the nineteenth century. Despite numerous systematic studies, their phylogenetic relationship with the other bivalve families is still uncertain. The Lithiotis facies yields other bivalve genera, among which a large multivincular mytiloid, provisionally determined as Isognomon (Mytiloperna) sp. ind. or Mytiloperna sp., is recorded in the literature. This taxon is here studied from a systematic point of view to clarify its taxonomic position and solve the open nomenclature adopted in the past. Here, we propose a new genus Pachygervillia and a new species Pachygervillia anguillaensis. The stratotype is located in the lower part of the Rotzo Formation (Calcari Grigi Group, Lower Jurassic), while the type locality is in the Lessini Mountains (Verona Province, Trento Platform, Southern Alps). This new species is characterized by a thick aragonitic inner shell layer with a fibrous, irregular, spherulitic, prismatic microstructure combined with a nacreous middle layer, both also occurring in species of the genera Lithiotis and Cochlearites of the family Plicatostylidae. This microstructural layering is here proposed as the main taxonomic character of the family, which is here emended and divided into the following two subfamilies: Plicatostylinae, yielding Lithiotis and Cochlearites with stick-like shells, and Pachygervilliinae nov. subfam., yielding Gervilleioperna, Lithioperna, Pachygervillia n. gen., and Pachyperna, previously placed within the subfamily Isognomoninae.

Calcitic Prisms of The Giant Seashell Pinna Nobilis Form Light Guide Arrays.

The shells of the Pinnidae family are based on a double layer of single-crystal-like calcitic prisms and inner aragonitic nacre, a structure known for its outstanding mechanical performance. However, on the posterior side, shells are missing the nacreous layer, which raises the question of whether there canbe any functional role in giving up this mechanical performance. Here, it isdemonstrated that the prismatic part of the Pinna nobilis shell exhibits unusual optical properties, whereby each prism acts as an individual optical fiber guiding the ambient light to the inner shell cavity by total internal reflection. This pixelated light channeling enhances both spatial resolution and contrast while reducing angular blurring, an apt combination for acute tracking of a moving object. Thesefindings offer insights into the evolutionary aspects of light-sensing and imaging and demonstrate how an architectured optical system for efficient light-tracking can be based on birefringent ceramics.

Red Seaweed Porphyra spp. (Bangiales) from Urimessing Waters of Ambon Island - Maluku

A study on the cultivation of Porphyra spp. has been carried out in the waters of Ambon Island. This plant is in great favor with local communities but has not been able to meet broader demands. The purpose of this research was to look into the future of mass culture. In the splashing zone, which is about 10 m above sea level, samples of gametophyte foliose or thalli were taken. The thallus was brought to the laboratory and maintained in a 100-liter container. During the rearing period, the thallus released spermatia and fertilized carpogonia. Carpogonia develop into carposporangia and release zygotospores outside the thallus. A small zygotospore develops into a large carpospore. Carpospores are the forerunners of new sporophytes if they find the correct substrate. In the laboratory, the nacre layer of pearl oyster shells was used to replace the natural substrates. Carpospores attached to the nacre layer germinated and grew into conchocelis. The conchocelis then develops the conchosporangia outward, followed by the release of the conchospores. Conchospores are a source of new thalli grown on polyethylene nylon nets. Conchospores that grew into new thalli on nylon nets were then moved to their natural environments so they could keep growing.

Structural and Functional Analyses of the Acidic and Basic Amino Acid Repeat Sequence (DDRK) in Pif 80 from Pinctada fucata on the Aragonite Crystal Surface Using NMR

Shellfish and crustaceans use calcium carbonate (CaCO3) as a protective shell and exoskeleton. CaCO3 is a major biomineral component in invertebrates. The Pinctada fucata shell contains two crystal polymorphs, with outer prismatic and inner nacreous layers. Diverse shell organic materials play significant roles in microstructure formation with organic–inorganic interactions. Pif 80 has a repeated acidic and basic amino acid low-complexity region that specifically binds to aragonite crystals. In this study, we aimed to elucidate the microstructure formation mechanism by analyzing the interaction between the low-complexity region and CaCO3. We used solution NMR to evaluate the structure and activity of the Pif 80 acidic region. We designed synthesis methods for aragonite nanoparticles that can be dispersed and rotated in solution. The results revealed that the “GDDRKDDRKG” peptide has the appropriate structure for aragonite surface binding, wherein the four carboxy groups of the Asp side chain are in the same plane, supported by Arg and Lys residues. The saturation transfer difference also supported this structure. These results suggest that the Pif 80 acidic region binds the aragonite crystal surface via Asp side chains with basic residues, providing new insights into the function of acidic and basic amino acids in biomineral formation.

Anodonta anatina midye kabuklarının yapısı ve sertlik özelliklerinin araştırılması

In this study, the shell structure of the freshwater mussel Anodonta anatina (Linnaeus, 1758) which has a widespread population in Gölbaşı Lake (Hatay) and is not economically exploited, was microscopically examined at a morphological level. It was determined that the shells of Anodonta anatina, which are not under significant fishing pressure, are mostly found discarded along the shores of the lake. This mussel species is important as a composite biological material with multifunctional roles in freshwater ecology. Considering the potential use of freshwater mussel shells as a biological material, an assessment of the shell structure, physical properties, mechanical strength, shell microstructure, and morphological characteristics of A. anatina was conducted. When cross-sections of the shell taken from the umbo, middle periostracum, and the region close to the pallial edge were examined in the dorsal-ventral direction, it was determined that the periostracum layer in the umbo region had a more prismatic and polygonal structure. The interior of the shell was found to consist of a shiny nacreous layer. In nacreous shell sections, it was observed that the nacreous layer contained more distinct layers near the pallial edge. Vickers microhardness tests were performed on individual shells, and it was found that the hardness value of the inner layer was the highest (625.5 ±172.7 HV), while the outer layer had a lower hardness value (531.5 ±110.7 HV). Based on XRF data, it was shown that the seashell powder is mainly composed of calcium oxide (98.8% wt., CaO) as a biological material.

Effect of ion and protein concentration of Ps19, a shell protein from Pteria sterna, on calcium carbonate polymorph

Calcium carbonate is present in many biological structures such as bivalve shell, which is composed mainly of two CaCO3 polymorphs: calcite and aragonite. However, exist other forms of calcium carbonate like vaterite and amorphous calcium carbonate (ACC) that are not commonly reported. Polymorph selection is influenced by salt concentration, cofactor ions, and the presence of shell matrix proteins (SMPs) which regulates calcium carbonate deposition, among other factors. In this study, calcium carbonate crystallization in vitro of four different saline solutions at two molarities was evaluated with increased concentrations of the Ps19 protein, an insoluble extracted protein from the shell of Pteria sterna, previously described as a promotor of aragonite platelet crystallization. In vitro crystallizations showed that Ps19 is capable to induce aragonite and calcite deposition in a dose-dependent manner, but also vaterite under ciertan conditions, acting as a promoter and inhibitor of crystallization. The results contribute to understand how Ps19 control precipitation of calcium polymorphs in the growth of the prismatic and nacre layer of the shell of P. sterna.