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.

Bone defects are a common complication of bone diseases, which often affect the quality of life and mental health of patients. The use of biomimetic bone scaffolds loaded with bioactive substances has become a focal point in the research on bone defect repair. In this study, composite scaffolds resembling bone tissue were created using nacre powder (NP) and sodium alginate (SA) through 3D printing. These scaffolds exhibit several physiological structural and mechanical characteristics of bone tissue, such as suitable porosity, an appropriate pore size, applicable degradation performance and satisfying the mechanical requirements of cancellous bone, etc. Then, platelet-rich fibrin (PRF), containing a mass of growth factors, was loaded on the NP/SA scaffolds. This was aimed to fully maximize the synergistic effect with NP, thereby accelerating bone tissue regeneration. Overall, this study marks the first instance of preparing a bionic bone structure scaffold containing NP by 3D printing technology, which is combined with PRF to further accelerate bone regeneration. These findings offer a new treatment strategy for bone tissue regeneration in clinical applications.

OBJECTIVE: Nano-hydroxyapatite (nHA)/ gel porous scaffolds loaded with WSM carriers are promising bone replacement materials that can improve osseointegration ability. This investigation aimed to evaluate the osteoinductive activity by implanting the composition of nano-hydroxyapatite (nHA)/ Gel porous scaffolds as a carrier of WSM via an animal model.
METHODS: WSM was extracted and nHA was added to the matrix to construct porous composite scaffolds. The dose-effect curve of WSM concentration and alkaline phosphatase (ALP) activity was made by culturing rat osteoblasts and examining the absorbance. Three different materials were implanted into critical size defects (CSD) in the skulls of rats, which were further divided into four groups: WSM nHA /Gel group, n-WSM nHA /Gel group, HA powder group, and control group.
RESULTS: WSM (150 μg/mL-250μg/mL) effectively improved the activity of ALP in rat osteoblasts. All rats in each group had normal healing. WSM-loaded nHA /Gel group showed better performance on newly-formed bone tissue of rat skull and back at 4th week and 8th week, respectively. At the 4th week, the network of woven bone formed in the WSM-loaded nHA/Gel scaffold material. At 8th week, the reticular trabecular bone in the WSM-loaded scaffold material became dense lamellar bone, and the defect was mature lamellar bone. In the subcutaneous implantation experiment, WSM-loaded nHA/Gel scaffold material showed a better performance of heterotopic ossification than the pure nHA/Gel scaffold material.
CONCLUSIONS: WSM promotes osteoblast differentiation and bone mineralization. The results confirm that the nHA/ Gel Porous Scaffold with Nacre Water-Soluble Matrix has a significant bone promoting effect and can be used as a choice for tissue engineering to repair bone defects.

Calcium carbonate (CaCO3) is abundant on Earth, is a major component of marine biominerals and thus of sedimentary and metamorphic rocks and it plays a major role in the global carbon cycle by storing atmospheric CO2 into solid biominerals. Six crystalline polymorphs of CaCO3 are known-3 anhydrous: calcite, aragonite, vaterite, and 3 hydrated: ikaite (CaCO3·6H2O), monohydrocalcite (CaCO3·1H2O, MHC), and calcium carbonate hemihydrate (CaCO3·½H2O, CCHH). CCHH was recently discovered and characterized, but exclusively as a synthetic material, not as a naturally occurring mineral. Here, analyzing 200 million spectra with Myriad Mapping (MM) of nanoscale mineral phases, we find CCHH and MHC, along with amorphous precursors, on freshly deposited coral skeleton and nacre surfaces, but not on sea urchin spines. Thus, biomineralization pathways are more complex and diverse than previously understood, opening new questions on isotopes and climate. Crystalline precursors are more accessible than amorphous ones to other spectroscopies and diffraction, in natural and bio-inspired materials.

Silicate scales are commonly incorporated into cellulose nanofiber (CNF) as functional fillers to enhance electrical insulation and UV-shielding properties. Nevertheless, the addition of substantial quantities of silicate scales in the quest for enhanced functional properties results in reduced interface bonding capability and compromised mechanical properties, thereby restricting their application. Here, inspired from nacre, layered composite paper with excellent mechanical strength, electrical insulation and UV-resistance properties was fabricated through vacuum assisted self-assembly using CNF, PVA and basalt scales (BS). Unlike the conventional blending strategy, the pre-mixed PVA and BS suspension facilitates the formation of Al-O-C bond, thereby enhancing the interfacial bonding between BS and CNF. Consequently, the composite paper (BS@PVA/PVA/CNF) containing 60 wt% BS demonstrates higher mechanical strength-approximately 140 % higher than that of BS/CNF composite paper, achieving a strength of 33.5 MPa. Additionally, it demonstrates enhanced dielectric properties, surpassing those of CNF paper by up to 107 %. Moreover, it exhibits robust ultraviolet-resistant aging performance, retaining ~87 % of its tensile strength after undergoing a simulated two-year aging period. As a result, this work presents a simple and innovative design strategy for enhancing interfacial bonding and optimizing layer structure, providing essential guidelines for large-scale production of high-performance insulation and aging-resistant composite paper.

Dental restorations are in increasing demand, yet their success rate strongly decreases after 5-10 years post-implantation, attributed in part to mismatching properties with the surrounding buccal environment that causes failures and wear. Among current research to address this issue, biomimetic approaches are promising. Nacre-like ceramic composites are particularly interesting because they combine multiple antagonistic properties making them more resistant to failure in harsh environment than other materials. With the rapid progress in 3D printing producing nacre-like structures has open up new opportunities not yet realised. In this paper, nacre-like composites of various compositions are reviewed in the context of hypothetical biomimetic dental restorations. Their structural, functional and biological properties are compared with those of dentin, enamel, and bone to determine which composition would be the most suitable for each of the 3 mineralized regions found in teeth. The role of complex microstructures and mineral orientations are discussed as well as 3D printing methods that allow the design and fabrication of such complex architectures. Finally, usage of these processes and anticipated prospects for next generation biomimetic dental replacements are discussed to suggest future research directions in this area. STATEMENT OF SIGNIFICANCE: With the current ageing population, dental health is a major issue and current dental restorations still have shortcomings. For the next generation of dental restorations, more biomimetic approaches would be desirable to increase their durability. Among current materials, nacre-like ceramic composites are interesting because they can approach the various structural properties found in the different parts of our teeth. Furthermore, it is also possible to embed self-sensing functionalities to enable monitoring of oral health. Finally, new recent 3D printing technologies now permit the fabrication of complex shapes with local compositions and local microstructures. With this current status of the research, we anticipate new dental restorations designs and highlight the remaining gaps and issues to address.

Nacreous composites offer significant potential for applications in structural damping materials, which require simultaneous high stiffness and damping properties. In this study, we propose that the incorporation of functionally graded tablets into nacreous composites can further enhance both stiffness and damping energy dissipation concurrently. Analytical formulae for the loss modulus, storage modulus, and loss factor, validated through a series of finite element analyses, were derived to investigate the effects of variations in tablet modulus, structural geometry, and constituent properties. Our analyses demonstrate that designing a parabolic modulus distribution in the tablets can yield optimal strengthening and damping results. Furthermore, the characteristic modulus variation degree, overlap length, and frequency emerged from the systematic optimization of loss and storage moduli. Additionally, numerical experiments and model predictions demonstrate that the loss modulus of functionally graded nacreous composites surpasses the predetermined design limit and is five times greater than that of existing homogeneous nacreous composites. Combining the developed theoretical model presented here with advanced 3D printing techniques would offer effective guidelines for designing and fabricating high-performance bio-inspired structural damping composites.

Color polymorphisms in molluscan shells play an important economic in the aquaculture industry. Among bivalves, shell color diversity can reflect properties such as growth rate and tolerance. In pearl oysters, the nacre color of the donor is closely related to the pearl color. Numerous genes and proteins involved in nacre color formation have been identified within the exosomes of the mantle. In this study, we analyzed the carotenoids present in the mantle of gold- and silver-lipped pearl oysters, identifying capsanthin and xanthophyll as crucial pigments contributing to coloration. Transcriptome analysis of the mantle revealed several differentially expressed genes (DEGs) involved in color formation, including ferric-chelate reductase, mantle genes, and larval shell matrix proteins. We also isolated and identified exosomes from the mantles of both gold- and silver-lipped strains of the pearl oyster Pinctada fucata martensii, revealing the extracellular transition mechanism of coloration-related proteins. From these exosomes, we obtained a total of 1223 proteins, with 126 differentially expressed proteins (DEPs) identified. These proteins include those associated with carotenoid metabolism and Fe(III) metabolism, such as apolipoproteins, scavenger receptor proteins, β,β-carotene-15,15\'-dioxygenase, ferritin, and ferritin heavy chains. This study may provide a new perspective on the nacre color formation process and the pathways involved in deposition within the pearl oyster P. f. martensii.

Nowadays, chronic diseases are the primary threat to public health and are getting younger. By taking the advantages of continuousness, convenience, and real-time response, wearable strain sensors have been given great attention to diagnose chronic diseases via analyzing the patient\'s health state. However, most physiological signals, such as limb tremor of Parkinson\'s disease, microexpression, and slight joint movement, are tiny and difficult to be detected. Therefore, the development of strain sensors characterized with ultrahigh sensitivity in a small strain range (ε < 10%) is urgent. Inspired by nacre\'s hierarchical structure, we have fabricated nacre-mimetic nanocomposites with \"brick-and-mortar\" architecture by employing polyacrylamide (PAM) and Ti3C2Tx MXene nanosheets through a layer-by-layer (LBL) spin-coating technique. The resultant nanocomposite-based strain sensor exhibits ultrahigh sensitivity in a small strain range (GF = 296.8, ε < 10%), attributed to the bioinspired hierarchical structure and hydrogen bond-enhanced interfacial interactions. In addition, a high reliability, broad working sensing range (453%), short response time (183 ms), skin-like tensile stress (7.2 MPa), and excellent durability (2000 cycles) are also achieved. Due to the ultrahigh sensitivity within a small strain, the reported strain sensor can accurately diagnose and distinguish Parkinson\'s disease symptoms, including thumb pill-rolling tremor, masked face (microexpression), intermittent shaking of the head, and limb cogwheel motion. This work provides new insights to design strain sensors with high sensitivity for monitoring tiny signals and for disease diagnosis.

Ocean acidification (OA) results from the absorption of anthropogenic CO2 emissions by the ocean and threatens the survival of many marine calcareous organisms including molluscs. We studied OA effects on adult shells of the abalone species Haliotis diversicolor and Haliotis discus hannai that were exposed to three pCO2 conditions (ambient, ∼880, and ∼1600 μatm) for 1 year. Shell periostracum corrosion under OA was observed for both species. OA reduced shell hardness and altered the nacre ultrastructure in H. diversicolor, making its shells more vulnerable to crushing force. OA exposure did not reduce the shell hardness of H. discus hannai and did not alter nacre ultrastructure. However, the reduced calcification also decreased its resistance to crushing force. Sr/Ca in the shell increased with rising calcification rate. Mg/Ca increased upon OA exposure could be due to a complimentary mechanism of preventing shell hardness further reduced. The Na/Ca distribution between the aragonite and calcite of abalone shells was also changed by OA. In general, both abalone species are at a greater risk in a more acidified ocean. Their shells may not provide sufficient protection from predators or to transportation stress in aquaculture.