Shell Nacre Research Articles

Design of bimetallic interpenetrating biomimetic structures and additive-casting synergetic manufacturing

Inspired by biological materials like shell nacre, biphase interpenetrating materials with alternating soft and hard phases significantly enhance mechanical properties. However, their application in metallic materials is still unexplored. This study investigates the microstructure and fracture patterns of steel/aluminum interpenetrating composites with a Diamond TPMS structure, fabricated via vacuum infiltration casting. We found that steel and aluminum form a biomimetic "brick-and-mortar" structure under the Diamond framework, significantly enhancing the composites' ductility and strength. The interfacial bonding layer, composed of Fe2Al5, Al8Fe2Si, and Al4.5FeSi, shows a hardness far exceeding the adjacent base materials. This hardness increases unevenly with distance from the interface. Tensile tests reveal that structurally periodic interpenetrating materials outperform both trapezoidal interpenetrating and planar materials. Upon fracturing, cracks initially form at the interfacial bonding layer and gradually spread into the interpenetrating region. Subsequently, under tensile and shear stress from mechanical interlocking, brittle fractures develop between aluminum components. The crack then extends into the steel framework, causing ductile fractures and complete failure of the composite.

Biomimetic aerogel coatings for flexible polyurethane foams with superior flame retardancy, mechanical flexibility and antibacterial properties

Flexible polyurethane foams (FPUFs) are widely used in various industries due to its high rebound characteristics, but its inherent flammability significantly affects its application. In this study, inspired by the structure of shell nacre, an aerogel coating with gelatin, boric acid and tetrakis hydroxymethyl phosphonium sulfate (THPS) as raw materials was designed. Owing to the hydrogen bonding interactions among the above molecules, the aerogel coating exhibits strong interfacial adhesion to the FPUF substrate, and the peel strength even surpasses the intrinsic strength of the FPUF matrix. Moreover, the coated FPUFs exhibit exceptional flame retardant and thermal insulation properties. The LOI value reaches as high as over 80 % and easily achieves a UL-94 V0 rating. During combustion, the coated FPUFs illustrate extremely low heat and smoke release. Meanwhile, the coated FPUFs still maintain excellent resilience. In addition, the THPS endows coated FPUFs with excellent antibacterial properties and exhibits a highly inhibition against Escherichia coli and Staphylococcus aureus.

Biomimetic lubricant-grafted surfaces on laser-textured microwell arrays with multifunctionality

Recently, various slippery liquid-infused porous surfaces (SLIPS) have been fabricated for the protection of various materials. However, these SLIPSs are limited by their underlying storage structure and superficial lubricant layer, showing poor durability. Herein, inspired by the high-strength structure of Shell nacre’s “brick-mud” layer, we fabricated an all-inorganic composite coating by using wet chemically etched MXene as a brick and an aluminum phosphate binder (AP) as mud. Then, a series of microwell-array structures were designed and prepared on the coating via nanosecond ultrafast laser writing ablation technology. Subsequently, the textured surface was modified by a silane coupling agent. Vinyl-terminated polydimethylsiloxane (PDMS) was tightly grafted onto the porous surface through a thiol-ene click reaction to obtain lubricant grafted texture surface (LGTS). The prepared LGTS showed good lubrication properties for multiple phases, including various liquids, ice crystals, and solids. It exhibits excellent chemical stability and mechanical durability under deionized water impact, centrifugal test, strong acid solutions, anti/de-icing cycles, and high-intensity friction. Thus, the proposed strategy for constructing robust LGTS will greatly promote theoretical research on super wetting interfacial materials and their applications in the fields of antifouling, anti/de-icing, and lubricating protection.

Influence of geographical origin and shell positions on nacre color and thickness in mabé pearl oysters Pteria penguin

To examine variations in nacre color and thickness in Pteria penguin oysters obtained from Tonga and Japan, a novel approach with a focus on their potential for mabé pearl production was used. Detailed analyses of color and microstructure revealed that the middle position of the right-valve nacre (position 1) primarily showed a reduction in yellow pigmentation. This was indicated by a decrease in the yellowness index (YI) and an increase in the whiteness index (WI). In contrast, the anterior and middle positions of the left-valve nacre (positions 2 and 3) consistently displayed a higher level of yellow pigmentation. A comparison of oysters from different geographical origin found that Tonga wild-caught oysters had significantly thicker nacre than Tonga culture-site oysters, suggesting the influence of probable genetic diversity and environmental factors on nacre formation. Notably, nacre at position 1 was generally thinner, while at positions 2 and 3 it was thicker, which would influence the resultant pearl quality and attributes. We demonstrate the significance of the nacre position on the valve for mabé pearl production: position 1 tended to produce white pearls with pronounced interference colors, whereas position 2 tended to yield gold pearls. Furthermore, our findings highlight the significant impact of the oysters' geographic origin on mabé pearl color and quality. This study emphasizes the importance of considering the position of shell nacre and the potential influences of the oysters' genetic origins and environmental factors on mabé pearl formation.

Guinea fowl eggshell structural analysis at different scales reveals how organic matrix induces microstructural shifts that enhance its mechanical properties

Guinea fowl eggshells have an unusual structural arrangement that is different from that of most birds, consisting of two distinct layers with different microstructures. This bilayered organization, and distinct microstructural characteristics, provides it with exceptional mechanical properties. The inner layer, constituting about one third of the eggshell thickness, contains columnar calcite crystal units arranged vertically as in most bird shells. However, the thicker outer layer has a more complex microstructural arrangement formed by a switch to smaller calcite domains with diffuse/interlocking boundaries, partly resembling the interfaces seen in mollusk shell nacre. The switching process that leads to this remarkable second-layer microstructure is unknown. Our results indicate that the microstructural switching is triggered by changes in the inter- and intracrystalline organic matrix. During production of the outer microcrystalline layer in the later stages of eggshell formation, the interactions of organic matter with mineral induce an accumulation of defects that increase crystal mosaicity, instill anisotropic lattice distortions in the calcite structure, interrupt epitaxial growth, reduce crystallite size, and induce nucleation events which increase crystal misorientation. These structural changes, together with the transition between the layers and each layer having different microstructures, enhance the overall mechanical strength of the Guinea fowl eggshell. Additionally, our findings provide new insights into how biogenic calcite growth may be regulated to impart unique functional properties. Statement of significanceAvian eggshells are mineralized to protect the embryo and to provide calcium for embryonic chick skeletal development. Their thickness, structure and mechanical properties have evolved to resist external forces throughout brooding, yet ultimately allow them to crack open during chick hatching. One particular eggshell, that of the Guinea fowl, has structural features very different from other galliform birds – it is bilayered, with an inner columnar mineral structure (like in most birds), but it also has an outer layer with a complex microstructure which contributes to its superior mechanical properties. This work provides novel and new fundamental information about the processes and mechanisms that control and change crystal growth during the switch to microcrystalline domains when the second outer layer forms.

In Vitro Osteogenesis Study of Shell Nacre Cement with Older and Young Donor Bone Marrow Mesenchymal Stem/Stromal Cells.

Bone void-filling cements are one of the preferred materials for managing irregular bone voids, particularly in the geriatric population who undergo many orthopedic surgeries. However, bone marrow mesenchymal stem/stromal cells (BM-MSCs) of older-age donors often exhibit reduced osteogenic capacity. Hence, it is crucial to evaluate candidate bone substitute materials with BM-MSCs from the geriatric population to determine the true osteogenic potential, thus simulating the clinical situation. With this concept, we investigated the osteogenic potential of shell nacre cement (SNC), a bone void-filling cement based on shell nacre powder and ladder-structured siloxane methacrylate, using older donor BM-MSCs (age > 55 years) and young donor BM-MSCs (age < 30 years). Direct and indirect cytotoxicity studies conducted with human BM-MSCs confirmed the non-cytotoxic nature of SNC. The standard colony-forming unit-fibroblast (CFU-F) assay and population doubling (PD) time assays revealed a significant reduction in the proliferation potential (p < 0.0001, p < 0.05) in older donor BM-MSCs compared to young donor BM-MSCs. Correspondingly, older donor BM-MSCs contained higher proportions of senescent, β-galactosidase (SA-β gal)-positive cells (nearly 2-fold, p < 0.001). In contrast, the proliferation capacity of older donor BM-MSCs, measured as the area density of CellTrackerTM green positive cells, was similar to that of young donor BM-MSCs following a 7-day culture on SNC. Furthermore, after 14 days of osteoinduction on SNC, scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) showed that the amount of calcium and phosphorus deposited by young and older donor BM-MSCs on SNC was comparable. A similar trend was observed in the expression of the osteogenesis-related genes BMP2, RUNX2, ALP, COL1A1, OMD and SPARC. Overall, the results of this study indicated that SNC would be a promising candidate for managing bone voids in all age groups.

Simple fabrication of anisotropic slippery lubricant-infused surface for directional transportation and anti-corrosion by metal-metal laminated composites

Slippery lubricant-infused surfaces with anisotropy for directional transportation have been widely researched and fabricated. However, the preparation of the required surface morphology remains complex and challenging. Inspired by the laminated structure found on natural shell nacre and slippery characteristics of nepenthes, a simple and universal method was provided to fabricate anisotropic slippery lubricant-infused surface. 304/TC4 metal-metal laminated composites were prepared by diffusion bonding 304 stainless steel and TC4 titanium alloy foils. A regular micro array with grooves was obtained through simple chemical etching. The widths of grooves and bulges, as well as the depths of grooves could be adjusted as needed. After the chemical modification, the lubricant was infused into grooves to obtain anisotropic slippery lubricant-infused surfaces. The directional transportations along the grooves of water droplet in air and bubbles underwater were achieved on the fabricated surfaces. Furthermore, the achieved surfaces demonstrated outstanding performance in anti-corrosion and anti-fouling. A noteworthy advantage of using laminated composites to fabricate anisotropic slippery lubricant-infused surfaces lies in its simplicity, universality, and repeatability. Based on the previous reports about laminated composites, the structure with grooves can been obtained by simple chemical etching. This method is suitable for various materials, including metal, ceramic, carbon material, and polymers. It has great potential application in water collection, directional transportations, anti-corrosion and anti-fouling.

A novel configuration design of strong and ductile (TiC + Ti5Si3)/Ti laminated composites

To solve the low ductility of the uniformly particle-reinforced composites, novel (TiC + Ti5Si3)/Ti laminated composites are fabricated by electrophoretic deposition (EPD) silicon (Si) powders + graphene oxide (GOs) and spark plasma sintering (SPS) technology. The microstructure evolution, mechanical properties, strengthening and fracture mechanisms of laminated composites were systematically studied. Results show that the GOs and Si powders are evenly attached to Ti foils after EPD, and the (TiC + Ti5Si3) reinforcements are in situ formed at the interface after SPS. TiC phases are distributed along the original interface, and most of the Ti5Si3 reinforcements are located in the Ti foil matrix. The 50 μm - 120 s sample possesses obvious shell nacre containing particular ‘‘brick-and-mortar’’ architecture structure. And the 100 μm - 120 s sample displays excellent room temperature tensile properties, with the ultimate tensile strength (UTS) of 759 MPa, yield strength (YS) of 688 MPa and elongation (EL) of 24.3 %. The change of microstructure leads to the increase of strength, which is caused by the solid-solution strengthening, grain boundary strengthening and reinforcements strengthening. At this time, the design of laminated structure can change the crack propagation direction, extend the crack propagation path and thereby increases the energy required for crack propagation, obstructing the fracture of composites. This work provides an effective method to prepare Ti matrix composites with synergy of strength and ductility.

Microstructure and mechanical properties of highly biomimetic brick-and-mortar structure Ti6Al4V/Al3Ti metal-intermetallic laminate composite

The brick-and-mortar structure of shell nacre allows for the simultaneous enhancement of strength and plasticity through the synergistic effect of multiple toughening mechanisms at different scales. In this work, a novel nacre-like brick-and-mortar structure Ti6Al4V/Al3Ti metal-intermetallic laminate (BMS-MIL) composite was successfully fabricated via vacuum hot pressing sintering method. The BMS-MIL composite is mainly composed of Al3Ti and Ti phases, with a small amount of Al2Ti and AlTi phases. Al3Ti is in the shape of polygonal platelet, and a 5–8 μm diffusion layer composed of Al2Ti and AlTi is distributed on the surface of the platelets. Ti6Al4V connects the platelets and is present in a continuous network frame structure. Compared with the layered structure Ti6Al4V/Al3Ti metal-intermetallic laminate (LS-MIL) composite, the fracture strain of BMS-MIL composite increases by 125.1% while maintaining high strength under load perpendicular to layer, and the compressive strength of BMS-MIL composite increases by 26.3% under load parallel to layer, respectively. Material isotropy in compressive properties has been significantly improved. In bending tests, the strength of the BMS-MIL composite is 1.9 times that of the LS-MIL composite. The brick-and-mortar structure’s excellent strengthening and toughening effect benefits from the enhancement of its crack constraint.

Novel Bone Void Filling Cement Compositions Based on Shell Nacre and Siloxane Methacrylate Resin: Development and Characterization.

Shell nacre from Pinctada species has been extensively researched for managing bone defects. However, there is a gap in the research regarding using shell nacre powder as a cement with improved biological and physicochemical properties. To address this, bone void filling cement was formulated by incorporating shell nacre powder and an organically modified ceramic resin (ormocer). The shell nacre powder was specifically processed from the shells of Pinctada fucata and analysed using thermogravimetric analysis (TGA), X-ray diffraction spectroscopy, Fourier transform infrared (FTIR), and Raman spectroscopy, confirming the presence of organic constituents and inorganic aragonite. Trace element analysis confirmed the eligibility of shell nacre powder for biomedical applications. Next, the ormocer SNLSM2 was synthesized through a modified sol-gel method. FTIR, Raman, TGA, and transmission electron microscopy studies revealed the presence of a ladder-structured siloxane backbone and methacrylate side chain. To develop chemical curable composite shell nacre cement (SNC), different amounts of shell nacre (24%, 48%, and 72%) were added to the SNLSM2 resin, and the impact on the physicochemical properties of the cement was studied. Among the compositions, SNC 72 exhibited significantly lower linear polymerization shrinkage (0.4%) and higher compressive (>100 MPa) and flexural strength (>35 MPa). SNC 72 was radiopaque, and the exotherm generated during the cement curing was minimal. Cytotoxicity studies with L929 cells revealed the non-cytotoxic nature of the cement. Overall, the findings of this study prove that the shell nacre cement is a promising candidate for managing bone voids.

Vitrimer-Assisted Construction of Boron Nitride Vertically Aligned Nacre-mimetic Composites for Highly Thermally Conductive Thermal Interface Materials

Modern electronic equipment with high integration and power consumption levels urges for more effective thermal interface materials (TIMs) to tackle its increasingly severe cooling issues. To effectively transfer the heat generated by electronic components to the radiator, the TIM is supposed to have a high through-plane thermal conductivity (λ⊥); however, achieving that proved devilishly challenging. Herein, inspired by the structure of the natural shell nacre and based on the construction of a cis-polybutadiene (BR) vitrimer network with reversible B–O bonds, the nacre-mimetic microstructure with vertically aligned hexagonal boron nitride (BN) was rationally designed and fabricated. Combining the hot-pressed orientation with the stacking-welding method, the vertically aligned BN/BR composite (VAC) was obtained by longitudinal slicing, and the designed microstructure with intense orientation was verified by scanning electron microscopy and small-angle X-ray scattering. As a result, the VAC reached an unprecedented λ⊥ of 14.1 W·m–1·K–1 as the BN content was 52 vol %, and the running chip temperature was greatly reduced compared with that of commercial TIM. Besides the superior thermal conductivity, the BN/BR composite has excellent electrical insulation and flame resistance. It is believed that the simple fabrication and extendibility of the biomimetic composites pave a new way for the design and preparation of high-performance TIMs.

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.

CaCO3 Crystals with Unique Morphologies Controlled by the Hydrogen-Bonded Supramolecular Assemblies of Ureido-Pyrimidinone-Amino Acid Derivatives.

Biomineral materials such as nacre of shells exhibit high mechanical strength and toughness on account of their unique "brick-mortar" multilayer structure. 2-Ureido-4[1H]-pyrimidinone (UPy) derivatives with different types of end groups, due to the self-complementary quadruple hydrogen bonds and abundant Ca2+ binding sites, can easily self-assemble into supramolecular aggregates and act as templates and skeleton in the process of inducing mineral crystallization. In this work, UPy derivatives were used as templates to induce the mineralization and growth of CaCO3 through a CO2 diffusion method. The morphology of CaCO3 crystals was modulated and analyzed by adjusting the synthesizing parameters including Ca2+ concentration, pH, and end groups. The results showed that, by the regulatory role of the mineralization template, it was easier to realize the multilayer crystal structure at a lower concentration of Ca2+ (less than 0.01 mol L-1). Under alkaline regulation, the quadruple hydrogen bonds would be destroyed, and the template's regulation effect on the morphology of CaCO3 crystals would be weakened. Moreover, by comparing different types of end groups, it was proven that the UPy derivatives with carboxylic acid groups (-COOH) played a crucial role in the process of CaCO3 crystallization with unique morphologies.

A genome-wide association study identifies SNPs and candidate genes associated with nacre color of pearl oyster Pinctada fucata martensii

Molluscan shell color polymorphism as a major economic factor in aquaculture has been of increasing interest to scientists. In pearl oyster, the trait of shell nacre color is abundant and play a major role in color during the pearl production process. To understand the genetic effect and potential underlying genes of nacre color trait, a genome-wide association study (GWAS) was performed in 830 individuals based our previous resequencing data. After GWAS, a total of 464 significantly associated SNP loci were identified and were mapped primarily onto chromosomes 14. In the 100-kb regions of the peak SNPs, some candidate genes may involve in the formation of shell golden nacre color were annotation, including LDR2, RDH12, BCOL, FN3–2 and CHI3L1, which have been reported to be involved in coloration. In addition, 11 haplotypes related nacre color were constructed. Successfully, one haplotype was verified in another population. In the block 6 of quantitative trait, the b* value (yellowness) of the haplotype ACA was significantly higher than that of the haplotype TGG in the validation population 1. The results should contribute to understanding of the molecular mechanisms of nacre coloration and useful for SNP-based genomic selection breeding in pearl oyster culture.

Interfacial Mechanical Behavior in Nacre of Red Abalone and Other Shells: A Review.

Interfaces between nacreous tablets are crucial to the outstanding mechanical properties of nacre in natural shells. Excellent research has been conducted to probe the effect of interfaces on strength and toughness of nacre, providing critical guidelines for the design of human-made laminated composites. This article reviews recent studies on interfacial mechanical behavior of nacre in red abalone and other shells, including experimental methods, analytical and numerical modeling. The discussions focus on the mechanical properties of dry and hydrated nacreous microstructures. The review concludes with discussions on representative studies of nacre-like composites with interfaces tuned using multiple approaches, and provides an outlook on improving the performance of composites with better interfacial controls.

Evolution of Epidermal Growth Factor (EGF)-like and Zona Pellucida Domains Containing Shell Matrix Proteins in Mollusks.

Several types of shell matrix proteins (SMPs) have been identified in molluskan shells. Their diversity is the consequence of various molecular processes, including domain shuffling and gene duplication. However, the evolutionary origin of most SMPs remains unclear. In this study, we investigated the evolutionary process EGF-like and zona pellucida (ZP) domains containing SMPs. Two types of the proteins (EGF-like protein (EGFL) and EGF-like and ZP domains containing protein (EGFZP)) were found in the pearl oyster, Pinctada fucata. In contrast, only EGFZP was identified in the gastropods. Phylogenetic analysis and genomic arrangement studies showed that EGFL and EGFZP formed a clade in bivalves, and their encoding genes were localized in tandem repeats on the same scaffold. In P. fucata, EGFL genes were expressed in the outer part of mantle epithelial cells are related to the calcitic shell formation. However, in both P. fucata and the limpet Nipponacmea fuscoviridis, EGFZP genes were expressed in the inner part of the mantle epithelial cells are related to aragonitic shell formation. Furthermore, our analysis showed that in P. fucata, the ZP domain interacts with eight SMPs that have various functions in the nacreous shell mineralization. The data suggest that the ZP domain can interact with other SMPs, and EGFL evolution in pterimorph bivalves represents an example of neo-functionalization that involves the acquisition of a novel protein through gene duplication.

Enhanced Mechanic Strength and Thermal Conductivities of Mica Composites with Mimicking Shell Nacre Structure

As the main insulation of high-voltage motors, the poor mechanical and thermal conductivities of mica paper restrict the motor’s technological advances. This paper prepared multilayer toughening mica composites with a highly ordered “brick-mud” stacking structure by mimicking the natural conch nacre structure. We investigated the mechanical, thermal, and breakdown properties by combined study of tensile strength, stiffness, thermal conductivity, and breakdown strength at varying mica and nanocellulose contents. The results show that thermal conductivity of the mica/chitosan composites were gradually enhanced with the increase in mica content and the composite shows the optimal synthetic performance at 50 wt% mica content. Further addition of the nanocellulose can extremely enhance the thermal conductivities of mica/chitosan composites. The composite with 5 wt% nanocellulose obtained the maximal thermal conductivity of 0.71 W/(m·K), which was about 1.7 times that of the mica/chitosan composite (0.42 W/(m·K)) and much higher than normal mica tape (0.20 W/(m·K)). Meanwhile, the breakdown strength and tensile strength of mica/chitosan/nanocellulose composite also demonstrated substantial improvement. The application of the mica/chitosan/nanocellulose composite is expected to essentially enhance the stator power density and heat dissipation ability of large-capacity generators and HV electric motors.

Design of Multi-Functional Superhydrophobic Coating via Bacterium-Induced Hierarchically Structured Minerals on Steel Surface.

The fabrication of an eco-friendly, multi-functional, and mechanically robust superhydrophobic coating using a simple method has many practical applications. Here, inspired by shell nacre, the micro- or nano-scale surface roughness that is necessary for superhydrophobic coatings was formed via Bacillus subtilis–induced mineralization. The biomineralized film coated with hexadecyltrimethoxysilane (HDTMS) exhibited superhydrophobicity with water contact angles of 156°. The biomimetic HDTMS/calcite-coating showed excellent self-cleaning, anti-icing, and anti-corrosion performances. Furthermore, mechanically robust superhydrophobicity could be realized by hierarchically structured biomineralized surfaces at two different length scales, with a nano-structure roughness to provide water repellency and a micro-structure roughness to provide durability. Our design strategy may guide the development of “green” superhydrophobic coatings that need to retain effective multi-functional abilities in harsh marine environments.

Color profile and microstructure of the nacre shell of an invasive freshwater mussel, Sinanodonta woodiana, at different elevations in West Java, Indonesia

The Chinese pond mussel Sinanodonta woodiana is an invasive freshwater mussel in Indonesia but has economic potential owing to the production of hemispherical pearls in their nacreous shell. To our knowledge, this study is the first to report on the species' shell nacre color profile and correlate it with microstructure and environmental factors at different elevations, from sea level to more than 1500 m. Samples from Lowland, Midland, and Highland elevations in West Java Province were observed and analyzed using the scanning electron microscope for shell microstructure. In addition, the nacre color was analyzed using spectrophotometry and estimated using the CIE Yxy color space and yellowness index. The nacre color ranged from gold to yellow and silvery. The microstructure at five positions on the shell was observed with a scanning electron microscope. The nacre with gold color had a thicker whole nacre layer, thinner nacre tablet thickness, and narrower surface nacre tablet area. In contrast, the nacre with silver color had a thinner whole nacre layer, thicker nacre tablet thickness, and greater surface nacre tablet area. The posterior position of shell nacre had a strong gold color with a high yellowness index, whereas the anterior and dorsal positions had a yellow color, and the central and ventral positions had a silver color. Mussels from the Midland locations displayed strong gold-colored nacre with a high yellowness index and high brightness. Based on these results, Midland areas are considered to have optimum environmental conditions for hemispherical pearl culture. S. woodiana shell with a thicker nacre layer and thinner nacre tablet shows a strong gold color, whereas a thinner nacre layer and thicker tablet nacre has a silvery color. We surmise that environments with high chlorophyll-a concentrations and low concentrations of total suspended solids result in the thicker nacre layer and the stronger gold color in the inner shell of S. woodiana.

Evaluation of remodeling and geometry on the biomechanical properties of nacreous bivalve shells

Mollusks have developed a broad diversity of shelled structures to protect against challenges imposed by biological interactions(e.g., predation) and constraints (e.g., pCO_2-induced ocean acidification and wave-forces). Although the study of shell biomechanical properties with nacreous microstructure has provided understanding about the role of shell integrity and functionality on mollusk performance and survival, there are no studies, to our knowledge, that delve into the variability of these properties during the mollusk ontogeny, between both shells of bivalves or across the shell length. In this study, using as a model the intertidal mussel Perumytilus purpuratus to obtain, for the first time, the mechanical properties of its shells with nacreous microstructure; we perform uniaxial compression tests oriented in three orthogonal axes corresponding to the orthotropic directions of the shell material behavior (thickness, longitudinal, and transversal). Thus, we evaluated whether the shell material’s stress and strain strength and elastic modulus showed differences in mechanical behavior in mussels of different sizes, between valves, and across the shell length. Our results showed that the biomechanical properties of the material building the P. purpuratus shells are symmetrical in both valves and homogeneous across the shell length. However, uniaxial compression tests performed across the shell thickness showed that biomechanical performance depends on the shell size (aging); and that mechanical properties such as the elastic modulus, maximum stress, and strain become degraded during ontogeny. SEM observations evidenced that compression induced a tortuous fracture with a delamination effect on the aragonite mineralogical structure of the shell. Findings suggest that P. purpuratus may become vulnerable to durophagous predators and wave forces in older stages, with implications in mussel beds ecology and biodiversity of intertidal habitats.