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1.
贝壳珍珠层不同取向弹性模量的研究   总被引:1,自引:0,他引:1  
研究天然生物材料的组织结构特征与其性能之间的关系对于材料的仿生有重要意义.在自制的激光测试设备上用三点弯曲法对贝壳珍珠层不同取向的弹性模量进行了研究,报道了不同取向和加载方式条件下弹性模量的变化规律。结果表明,在平行和倾斜于生长纹路方向上弹性模量的平均值分别为60.3GPa和56.7GPa,而垂直于纹路方向的为48GPa,呈现出各向异性。弹性模量的各向异性主要来自于珍珠层微观组织结构和贝壳生长纹结构的特点.  相似文献   
2.
We measured distribution patterns of hardness and elastic modulus by nanoindentation on shells of the rhynchonelliform brachiopod Mergerlia truncata and the linguliform brachiopods Discradisca stella and Lingula anatina. The rhynchonelliformea produce calcitic shells while the linguliformea produce chitinophosphatic shells. Dorsal and ventral valves, commissure and hinge of the calcitic shell of M. truncata show different nanohardness values (from 2.3 to 4.6 GPa) and E-modulus (from 52 to 76 GPa). The hardness of the biocalcite is always increased compared to inorganic calcite. We attribute the effects to different amounts of inter- and intracrystalline organic matrix. Profiles parallel to the radius of curvature of the valves cutting through the different layers of shell material surprisingly show quite uniform values of nanohardness and modulus of elasticity. Nanoindentation tests on the chitinophosphatic brachiopods D. stella and L. anatina reflect the hierarchical structure composed of laminae with varying degree of mineralization. As a result of the two-phase composite of biopolymer nanofibrils reinforced with Ca-phosphate nanoparticles, nanohardness, and E-modulus correlate almost linearly from (H = 0.25 GPa, E = 2.5 GPa) to (H = 2.5 GPa, E = 50 GPa). The mineral provides stiffness and hardness, the biopolymer provides flexibility; and the composite provides fracture toughness. Gradients in the degree of mineralization reduce potential stress concentrations at the interface between stiff mineralized and soft non-mineralized laminae. For the epibenthic chitinophosphatic D. stella the lamination is also present but less pronounced than for the infaunal L. anatina, and the overall distribution of material strength in the cross-sectional profile shows a maximum in the center and a decrease towards the inner and outer shell margins (modulus of elasticity from 30 to 12 GPa, hardness from 1.7 to 0.5 GPa). Accordingly, the two epibenthic forms, calcitic M. truncata and chitinophosphatic D. stella display fairly bulky (homogeneous) nanomechanical properties of their shell materials, while the burrowing infaunal L. anatina is distinctively laminated. The strongly mineralized laminae, which provide the strength to the shell, are also brittle, but keeping them as thin as possible, allows some bending flexibility. This flexibility is not required for the epibenthic life style.  相似文献   
3.
Mineral bridges in nacre   总被引:1,自引:0,他引:1  
We confirm with high-resolution techniques the existence of mineral bridges between superposed nacre tablets. In the towered nacre of both gastropods and the cephalopod Nautilus there are large bridges aligned along the tower axes, corresponding to gaps (150–200 nm) in the interlamellar membranes. Gaps are produced by the interaction of the nascent tablets with a surface membrane that covers the nacre compartment. In the terraced nacre of bivalves bridges associated with elongated gaps in the interlamellar membrane (>100 nm) have mainly been found at or close to the edges of superposed parental tablets. To explain this placement, we hypothesize that the interlamellar membrane breaks due to differences in osmotic pressure across it when the interlamellar space below becomes reduced at an advanced stage of calcification. In no cases are the minor connections between superimposed tablets (<60 nm), earlier reported to be mineral bridges, found to be such.  相似文献   
4.
Mollusc shell formation takes place in a preformed extracellular matrix, composed of insoluble chitin, coated with proteins and dissolved macromolecules. The water-soluble matrix is known to have a strong influence on the growth of CaCO(3), whereas the role of the insoluble matrix on mineralization is unclear. Therefore, we mineralized the EDTA (ethylenediaminetetraacetic acid) insoluble organic matrix of abalone nacre with a modified double-diffusion set-up, where the diffusing solutions were constantly renewed. Control experiments were performed with cellulose and chitosan foils. The mineralized matrices/foils were analyzed with SEM. We show that the insoluble matrix of abalone nacre induces the growth of flat and roughly polygonal CaCO(3) crystals. In some of the experiments with the insoluble matrix, the growth of three-dimensional parallel sheets of densely packed platelets inside the insoluble matrix was observed. XRD on these samples revealed that they consist of oriented aragonite.  相似文献   
5.
Nacre of Pinctada margaritifera displays a number of interesting biological activities on bone, mainly concentrated in a water-soluble organic matrix representing 0.24% of the nacre weight. Dialysis of that matrix through 8 kDa and 1 kDa cut-off membranes showed that 60% of it is made of small molecules of molecular masses below 1 kDa. Reversed-phase high-performance liquid chromatography of the small molecule fractions and subsequent electrospray ionization mass spectrometric analysis of 19 fractions thereof indicated the presence of at least 110 different molecules, in the range 100 Da–700 Da. Evidence for aggregate-forming properties of the small molecules was given. Amino acid analysis revealed that most of the small molecules were not peptides and tandem mass spectrometric gas-phase fragmentations clearly indicated a structural relationship between several molecules. Intriguingly, differences of a single Dalton between mono-charged ions peaks were observed. Further, approximately 40 analytes could be arranged in a ladder-like manner with mass spaces of 57 Da. Some of the water-soluble peptide sequences obtained after MS/MS fragmentation revealed that the 57 Da shift corresponds to the repetition of glycine residues. Furthermore, the exchange of glycine against alanine explains the 14 Da shift observed between some peptides. These data show for the first time that small molecules, especially peptides, are prevalent components of nacre. The molecular species described in this report might have a functional role in nacre.  相似文献   
6.
Formation of nacre (mother-of-pearl) is a biomineralization process of fundamental scientific as well as industrial importance. However, the dynamics of the formation process is still not understood. Here, we use scanning electron microscopy and high spatial resolution ion microprobe depth-profiling to image the full three-dimensional distribution of organic materials around individual tablets in the top-most layer of forming nacre in bivalves. Nacre formation proceeds by lateral, symmetric growth of individual tablets mediated by a growth-ring rich in organics, in which aragonite crystallizes from amorphous precursors. The pivotal role in nacre formation played by the growth-ring structure documented in this study adds further complexity to a highly dynamical biomineralization process.  相似文献   
7.

Background

Color polymorphism in the nacre of pteriomorphian bivalves is of great interest for the pearl culture industry. The nacreous layer of the Polynesian black-lipped pearl oyster Pinctada margaritifera exhibits a large array of color variation among individuals including reflections of blue, green, yellow and pink in all possible gradients. Although the heritability of nacre color variation patterns has been demonstrated by experimental crossing, little is known about the genes involved in these patterns. In this study, we identify a set of genes differentially expressed among extreme color phenotypes of P. margaritifera using a suppressive and subtractive hybridization (SSH) method comparing black phenotypes with full and half albino individuals.

Results

Out of the 358 and 346 expressed sequence tags (ESTs) obtained by conducting two SSH libraries respectively, the expression patterns of 37 genes were tested with a real-time quantitative PCR (RT-qPCR) approach by pooling five individuals of each phenotype. The expression of 11 genes was subsequently estimated for each individual in order to detect inter-individual variation. Our results suggest that the color of the nacre is partially under the influence of genes involved in the biomineralization of the calcitic layer. A few genes involved in the formation of the aragonite tablets of the nacre layer and in the biosynthesis chain of melanin also showed differential expression patterns. Finally, high variability in gene expression levels were observed within the black phenotypes.

Conclusions

Our results revealed that three main genetic processes were involved in color polymorphisms: the biomineralization of the nacreous and calcitic layers and the synthesis of pigments such as melanin, suggesting that color polymorphism takes place at different levels in the shell structure. The high variability of gene expression found within black phenotypes suggests that the present work should serve as a basis for future studies exploring more thoroughly the expression patterns of candidate genes within black phenotypes with different dominant iridescent colors.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1776-x) contains supplementary material, which is available to authorized users.  相似文献   
8.
Tissue inhibitors of metalloproteinases (TIMPs) are nature inhibitors of matrix metalloproteinases and play a vital role in the regulation of extracellular matrix turnover, tissue remodeling and bone formation. In this study, the molecular characterization of TIMP and its potential function in nacre formation was described in pearl oyster Pinctada martensii. The cDNA of TIMP gene in P. martensii (Pm-TIMP) was 901 bp long, containing a 5′ untranslated region (UTR) of 51 bp, a 3′ UTR of 169 bp, and an open reading fragment (ORF) of 681 bp encoding 226 amino acids with an estimated molecular mass of 23.37 kDa and a theoretical isoelectric point of 5.42; The predicted amino acid sequence had a signal peptide, 13 cysteine residues, a N-terminal domain and a C-terminal domain, similar to that from other species. Amino acid multiple alignment showed Pm-TIMP had the highest (41%) identity to that from Crassostrea gigas. Tissue expression analysis indicated Pm-TIMP was highly expressed in nacre formation related-tissues, including mantle and pearl sac. After decreasing Pm-TIMP gene expression by RNA interference (RNAi) technology in the mantle pallium, the inner nacreous layer of the shells showed a disordered growth. These results indicated that the obtained Pm-TIMP in this study participated in nacre formation.  相似文献   
9.
The nacre of mollusk shells is distinguished by an exceptional mechanical efficiency which is derived essentially from its lamellar structure and frequently acts as a source of inspiration for the development of biomimetic materials. The structure and mechanical properties of nacre have been intensively investigated with a special focus on its toughening strategies; nevertheless, the fracture mechanisms, more specifically the critical stress/strain conditions for the failure of nacre, and the effects of structural orientation and hydration state remain largely unexplored. Here uniaxial compression tests were performed on nacre of both dry and hydrated states with different off-axis angles, i.e., the inclination of loading axis with respect to the lamellar structure, ranging from 0° to 90°. The mechanical properties and fracture characteristics of nacre and their dependences on the structural orientation and hydration state were elucidated in terms of mechanics behind failure. Quantitative relationships were established between the mechanical properties and off-axis angle based on different failure criteria. The competition between the fracture modes of fragmentation and shearing was quantified by comparing their respective driving force and resistance on the interfacial plane. This study may aid the understanding on the mechanical behavior of nacre and nacre-inspired synthetic materials and promote a better replication of the underlying design principles of nacre in man-made systems.  相似文献   
10.
In vitro culture of mantle tissue of the abalone Haliotis varia Linnaeus   总被引:1,自引:0,他引:1  
The study is aimed at developing a technology for the production of in vitro pearl through tissue culture of mantle of the abalone, Haliotis varia Linnaeus, as the production of free and spherical pearls in vivo is rather difficult in abalones. In the basic study, the cell yield was intensified from the explant after 24h incubation. Among the cells liberated, the granulocytes were dominant over hyalinocytes. The size of granulocytes ranged from 3 to 16 microm and of hyalinocytes from 13 to 18 microm. Fibroblast-like cells appeared in cultures after day 2. Both granulocytes and hyalinocytes developed pseudopodial-like extensions in all directions and formed organic matrix. Granulocytes contained granules in the cytoplasm. Specific granules were responsible for nucleation of crystals. Some crystals exhibited green colour resembling mother of pearl of abalone. scanning electron microscope (SEM) study revealed the oolitic amorphous state and rhombohedral state of crystals. Its analysis through energy dispersive X-ray microanalyzer (EDS) indicated the presence of calcium. The rhombohedral crystals under polarized light showed its high birefringence (0.18) and uniaxial optically negative calcite nature with high content of calcium. A mean survival of cells was found to be 102 days in T 25 flasks and 32 days in petri dishes. Growth of cells was studied. Thirty percent of cultures were found to have contaminated during the study. The study provides basic knowledge in the development of a technology for in vitro pearl production.  相似文献   
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