In-vitro study on calcium carbonate crystal growth mediated by organic matrix extracted from fresh water pearls

For the purpose of studying the mediation of organic matrix on the crystallization of calcium carbonate, water soluble matrix (WSM), acid soluble matrix (ASM) and acid insoluble matrix (AIM) were extracted from aragonite pearls and vaterite pearls respectively. Then, in-vitro calcium carbonate crystallization experiments under the control of these six organic matrices were carried out in the present study. Scanning electron microscopy (SEM) was utilized to observe the morphology of CaCO₃ and Raman spectroscopy as a powerful technique was used to distinguish the crystal polymorph. Influences of the six kinds of organic matrices on the calcium carbonate crystal growth are proposed. ASM of vaterite pearls can induce vaterite to crystallize and WSM of aragonite pearls mediates to produce aragonite crystals. The single AIM membranes of the two pearls have no pronounced effect on the CaCO₃ crystallization. Additionally, the crystal size obtained with the additive of WSM of the two kinds of pearls is smaller than that with the additive of ASM. Moreover, self-assembly phenomenon in the biomineralization process and the distorted morphology calcite are observed. Current results demonstrate important aspects of matrix protein-controlled crystallization, which is beneficial to the understanding of nacre biomineralization mechanism. Further study of the precise control of these matrix proteins on CaCO₃ crystal growth is being processed.     

What is the difference in organic matrix of aragonite vs. vaterite polymorph in natural shell and pearl? Study of the pearl-forming freshwater bivalve mollusc Hyriopsis cumingii

Aragonite pearl, vaterite pearl and shell nacre of the freshwater mollusc Hyriopsis cumingii (Zhejiang province, China) were chosen to analyze microstructure and organic composition in the different habits of calcium carbonate. SEM and TEM were used to reveal the microstructure and mineralogical phase. We found that tablets in vaterite exhibited more irregular texture and were packaged with more organic matrices than in aragonite forms. Then a peculiar method was introduced to extract water soluble matrix (WSM), acid soluble matrix (ASM) and acid insoluble matrix (AIM) from the three samples, and biochemical analysis of these organic matrixes involved in crystal formation and polymorph selection was carried out. High performance liquid chromatography (HPLC) confirms the hydrophobic pattern of the organic matrix intermingled with mineral, the opposite of the early mobilizable water soluble fraction. Amino acid composition confirms hydrophobic residues as major components of all the extracts, but it reveals an imbalance in acidic residues rates in WSM vs. ASM and in aragonite vs. vaterite. Electrophoresis gives evidence for signatures in proteins with a 140 kDa material specific for aragonite in WSM. Conversely all ASM extracts reveal the presence of about 55 kDa components, including a discrete band in vaterite extract.     

淡水珍珠的生物矿化机理研究进展

碳酸钙广泛存在于生物矿物中, 是地球上最普遍的生物矿物之一。贝壳和珍珠的主要组成部分为碳酸钙无机相。我国淡水养殖珍珠多数品质优异, 具有良好的珍珠光泽。该种珍珠以文石晶型碳酸钙为无机相, 称为文石珍珠。近年来, 在我国淡水养殖珍珠中发现了球文石的存在, 球文石的出现是导致珍珠失去光泽、降低质量的主要原因。本文对比阐述了淡水文石珍珠和球文石珍珠的微观结构与性能, 总结了与珍珠层有关的体外模拟碳酸钙生物矿化的实验结果, 提出了珍珠层生物矿化机理未来的研究方向。     

Characterization of vaterite in low quality freshwater-cultured pearls

Vaterite is a very unstable phase of calcium carbonate rarely occurring in nature. We report a discovery of vaterite in the low quality freshwater-cultured pearls of the shell Hyriopsis cumingii (Lea). Experimental evidences are given by optical microscope, micro-infrared spectroscope and X-ray diffraction pattern. The formation mechanism of vaterite in these special pearls is discussed.     

The co-effect of organic matrix from carp otolith and microenvironment on calcium carbonate mineralization

In vitro mineralization experiment is an effective way to study the effect of organic matrix on calcium carbonate crystallization, and to reveal the relationship between organic matrix and inorganic crystal in natural biominerals. In natural biominerals, organic matrix plays an important role in crystal formation and stability, together with microenvironment changes, they can affect crystal polymorph, morphology, density, size, orientation etc.In this work, we systematically studied the effects of different organic matrices in fish otoliths, the organic matrix concentration changes, as well as the co-effect of organic matrices with temperature, pH value and Mg ion changes in the in vitro CaCO₃ mineralization experiments.The organic matrix and concentration change experiments prove that water soluble matrix (WSM) plays an important role in crystal form transition. It can induce CaCO₃ crystals with same crystal polymorph as the otolith from which organic matrix was extracted. The temperature change experiment proves that CaCO₃ has a tendency to form calcite, vaterite, and then aragonite in priority as temperature goes up. Under different temperature, WSM from lapillus/asteriscus still has the effect to mediate different CaCO₃ crystals. The pH change experiment shows that, near the neutral environment, as pH value goes up, calcites have a tendency to form crystal aggregates with more faces exposed, the organic matrix still keeps crystal mediation effect. The Mg^2 + experiment shows that, Mg ion can promote aragonite formation, together with lapillus organic matrix, aragonites with different shapes are formed.     

The incorporation of polar monomers in copolymers based on styrene and divinylbenzene obtained from glycerol suspension polymerization

Porous copolymer networks based on styrene (STY) and divinylbenzene (DVB) containing polar monomer (methacrylamide — MAM, methacrylic acid — MAA or acrylonitrile — ACN) were prepared by suspension polymerization using glycerol as a dispersant medium. Poly(styrene-co-methacrylamide-co-divinylbenzene), poly(styrene-co-methacrylic acid-co-divinylbenzene) and poly(styrene-co-acrylonitrile-co-divinylbenzene) were synthesized using mixtures of toluene with 2-butanone, toluene and 2-butanone and n-heptane with ethylacetate, respectively at different dilutions: 50%, 100% and 120% (v/v). The copolymers were characterized by bulk density, infrared spectrometry (FTIR) and elemental analysis (CHN). Morphological features of the copolymer pearls were evaluated by microscopic analysis and correlations between porous structure and parameters of reaction were found. The copolymers presented high incorporation of polar monomers. The pearl porosities and visual appearances had a strict relation with the monomer type and the dilution degree employed in synthesizing them.     

Controlled synthesis of calcium carbonate nanocrystals with multi-morphologies in different bicontinuous microemulsions

The nucleation and growth of calcium carbonate nanocrystals were studied in two types of bicontinuous microemulsions, consisted of P-octyl polyethylene glycol phenylether (OP)/n-amyl alcohol/cyclohexane/water, and the above microemulsion containing dl-aspartic acid (dl-Asp). The produced CaCO₃ nanocrystals were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FT-IR) and X-ray diffraction (XRD). The results indicated that OP and dl-Asp used as soft template could control synthesis of CaCO₃ nanocrystals well. The various shapes of CaCO₃ nanocrystals, such as solid sphere, network, whisker, rod, and hollow sphere were successfully prepared by altering the concentration of the reactants, adding dl-Asp, and adjusting the pH values of dl-Asp/CaCl₂ aqueous solution. Sole calcite phase was obtained in OP bicontinuous microemulsion. The presence of dl-Asp was helpful for the formation of thermodynamically unstable vaterite phase. In OP/dl-Asp bicontinuous microemulsion, the higher pH value of dl-Asp/CaCl₂ aqueous solution is, the more vaterite will be formed. A nucleation-limited growth and limited aggregation (NGA) model was used to explain growth mechanism of the network-like calcium carbonate in this study.     

Calcium carbonate growth in the presence of water soluble cellulose ethers

Calcium carbonate precipitation was performed in the presence of methyl cellulose (MC) and two kinds of hydroxyethyl cellulose (HEC FD-10000, HEC FD-30000). The results demonstrated that the final product morphology and structure of CaCO₃ crystals are highly sensitive to the concentration of the cellulose ethers aqueous solution. By precisely controlling their concentrations, all these three cellulose ethers solutions have the ability of protecting metastable vaterite from thermodynamically transforming into stable calcite. The intermediate products investigation showed to some extent the phase transformation of calcium carbonate in its growing process from metastable vaterite to calcite and indicated that the calcium carbonate crystal growth in HEC solutions occurs through dissolution and reprecipitation process. Calcium carbonate growth in both presence of HEC and ethanol or Mg²⁺ was also examined. This work demonstrates the potential of water soluble cellulose ethers in controlling biominerals crystallization and growth. The results are revelatory for biomineralization and fabricating new organic–inorganic hybrids based on cellulose derivatives.     

Control the polymorphism and morphology of calcium carbonate precipitation from a calcium acetate and urea solution

Two metastable calcium carbonate polymorphs, rod-like aragonite and spherical vaterite are selectively formed in this study. Aragonite rods were synthesized from a calcium acetate (Ca(AC)₂) and urea (CO(NH₂)₂) solution under a given condition. In contrast, the addition of polyacrylamide (PAM) and oleic acid results in the formation of spherical vaterite. The morphology, size and crystal structure were characterized by means of Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and X-ray diffraction (XRD). The results show that PAM and oleic acid can be used as additives to select the polymorph from aragonite and vaterite. The contact angle of the modified products reached 112.49°. We have succeeded in surface modification of particles in situ at the same time.     

Photoemission studies of polymorphic CaCO3 materials

The surface analysis of polymorphic calcium carbonate (CaCO₃) compounds, namely, calcite, aragonite, and vaterite were carried out by X-ray photoelectron spectroscopy (XPS). XPS results clearly demonstrate that vaterite is different from the other two and exhibit a low binding energy (BE) for all its constituent elements. It is attributed to the perpendicular orientation of CO₃²⁻ to ab plane in vaterite. Aragonite shows less calcium and more oxygen and indicates the surface is carbonate terminated. Intergrowth of calcite and aragonite and natural dolomite samples were also analysed and compared with the above CaCO₃ compounds. Ca:Mg=3 suggest that the dolomite surface is dominated by Ca.     

A novel route to prepare the metastable vaterite phase of CaCO3 from CaCl2 ethanol solution and Na2CO3 aqueous solution

Vaterite, the least stable phase among three anhydrous polymorphs of calcium carbonate (CaCO₃), was prepared via the reaction between the ethanol solution of calcium chloride (CaCl₂) and the aqueous solution of sodium carbonate (Na₂CO₃), which is named ethanol-calcium method. The effects of aging times and reaction temperatures on the formation of vaterite were investigated. The polymorphs and morphologies were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively, and Fourier transform infrared spectroscopy (FT-IR) was used to verify the existence of vaterite. XRD results indicate that the amount of vaterite decreases from 90.4% to 81.4% as increasing in aging times from 0?min to 42?h and decreases from 85.8% to 70.2% as increasing in reaction temperatures from 0?°C to 60?°C. SEM results show that vaterite and calcite as-prepared are their typical morphologies of spherical and rhombohedral, respectively. This research extends the route to prepare the metastable vaterite and provides new insights into its controllable synthesis.     

Features of positronium migration in a solid containing nanopores, by an example of sorption and annihilation of positrons in vaterite

The features of migration of positrons in the bulk of vaterite (metastable modification of CaCO₃) were studied using positron annihilation lifetime spectroscopy (PALS). Comparison of the lifetime of ortho-positronium determined from the PALS data, which corresponds to the time of its residence in the vaterite nanopores, with the absorption results (BET adsorption isotherm) allowed evaluation of the diffusion coefficient of positronium in the perfect sections of the vaterite crystal lattice, equal to 0.4 × 10^?1 cm² s^?1.     

Facile synthesis and characterization of hydrophobic vaterite CaCO3 with novel spike-like morphology via a solution route

Hydrophobic spike-like vaterite CaCO₃ composed of nanoparticles with an average size of 100 nm has been successfully synthesized via a simple synthetic method. The crystallization of vaterite CaCO₃ was fabricated by the reaction of CaCl₂ with Na₂CO₃ in ethanol-water solvents in the presence of oleic acid. The as-prepared products were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and contact angle analysis. The characterization results revealed that oleic acid played an important role in determining the phase and morphology of the sample. In addition, the surface properties of the vaterite CaCO₃ changed from hydrophilic to hydrophobic. The contact angle of the modified CaCO₃ reached 95.8°.     

Cotton wool-like poly(lactic acid)/vaterite composite scaffolds releasing soluble silica for bone tissue engineering

Cotton wool-like poly(l-lactic acid) and siloxane-doped vaterite (SiV) composite scaffolds were prepared with a modified electrospinning system for bone tissue engineering applications. The effects of changing the SiV content in the materials from 10 to 30 wt% on elasticity and the ability to release calcium ions and soluble silica were evaluated. The elasticity of the cotton wool-like composites was almost the same as that of the PLLA from the results of compressibility and recovery tests. The materials released calcium ions for more than 56 days and soluble silica for 28–56 days in a tris buffer solution (pH 7.4). Mouse osteoblast-like cells (MC3T3-E1 cells) were cultured on/in the cotton wool-like materials or the fibremats out of the same composite materials as that used for the cotton wool-like materials. The cells penetrated into and proliferated inside the cotton wool-like materials, although they mainly adhered on the fibremat surface.     

Antimicrobial coatings — obtaining and characterization

In this paper, we present inorganic–organic hybrid coatings with polymer matrix (water soluble) that contain silver nanoparticles (AgNPs). The structure and morphology of coating materials were determined by infrared spectroscopy (FT–IR) and scanning electron microscopy (SEM). Therefore, the antimicrobial activities and mechanisms of coatings for several pathogenic bacteria (Bacilius cereus and Staphylococcus aureus) were investigated. It was demonstrated that the obtained material with silver nanoparticles keep their antimicrobial effect even if they are subjected to several cycles of washing with water and detergent.     

On the kinetics of phase transformations of dried porous vaterite particles immersed in deionized and tap water

Calcium carbonate exists in three allotropic forms: vaterite, aragonite and calcite. Metastable vaterite can be easily transformed into calcite and/or aragonite via different routes. We report how dry vaterite particles transform into aragonite and calcite when they are immersed into DeIonized water (DI) or tap water without additives at different temperature (22, 40 and 60?°C) with and without stirring. We show that the transformation rate of vaterite into more stable crystallographic forms is influenced not only by temperature but also by stirring and water purity. Low temperature, absence of stirring and absence of ions in water significantly slow down the kinetics of transformation of vaterite. Additionally, water purity influences the nature of the allotropic phase obtained after transformation. High temperatures and DI water favor the transformation of vaterite into single crystalline nanowires of aragonite, while tap water yields the transformation of vaterite into calcite. The absence of aragonite in tap water at high temperature can be explained by the presence of sulfate ions, which inhibit the formation of this phase. On the contrary, Mg²⁺ ions tend to stabilize vaterite.     

Molluscan biomineralization: The proteinaceous shell constituents of Pinna nobilis L.

The shell of molluscs is a remarkable example of a natural composite biomaterial, synthesized at ambient temperature. Consequently, many consider it as a model for trying to develop at little cost new biomimetic materials of superior mechanical properties. The peculiar resistance of shells to fracture lies in an organic matrix, which is closely associated with the mineral phase. This matrix regulates the crystal growth, by allowing nucleation of the crystals only where appropriate, by favoring crystal elongation in privileged directions, and by inhibiting their growth. This matrix is a mixture of glycoproteins and polysaccharides, the primary structure and function of which are poorly known. Pinna nobilis, the Mediterranean fan mussel, is one of the few molluscs for which molecular data on shell proteins are available. In the present paper, we review what is known, at molecular level, on the macromolecular constituents of the shell of P. nobilis by describing three proteins, the characterization of which is still going on: the first one, mucoperlin, is specific of the nacreous layer. The two others were obtained from the calcitic prismatic layer and one of them was localized by immunogold and further tested to check its ability to modify the shapes of CaCO3 crystals. The data shown here, together with data obtained from the pearl oyster or the abalone, put into question some common ideas about molluscan mineralization.     

Extraction of radionuclides from aqueous HNO3 by adducts of complex inorganic acids with monosubstituted polyethylene glycols

The adducts of complex inorganic acids (CIAs) with monosubstituted derivatives of polyethylene glycols (PEGs) were prepared in aqueous acids. These adducts are poorly soluble in water (below 1 g/l) and readily soluble in polar organic solvents (up to 400 g/l). The adduct stoichiometry is a function of acidity, and the physicochemical and extraction characteristics of adducts depend on particular PEG and CIA. With increasing PEG content in the adducts, their extractive power decreases, the solubility in polar organic solvents increases, and the solubility in water passes through a minimum. All these adducts are highly resistant to hydrolysis and radiation. The extraction of Cs, Sr, Ba, Eu, and Am from aqueous HNO₃ with solutions of phosphomolybdic and hexachloroantimonic acid adducts with oxyethylated n-nonylphenol in organic solvents was studied.     

Characteristic crystal orientation of folia in oyster shell,Crassostrea gigas

The thin sheets of calcite, termed folia, that make up much of the shell of an oyster are composed of foliated lath. Folia of the giant Pacific oyster (Crassostrea gigas) were examined using TEM (transmission electron microscopy) and tested using microindentation and nanoindentation techniques. Analysis of the Kikuchi patterns obtained from the folia showed that there are two types (type I and type II) of preferred orientation, with an angle of around 70° between them. Nanoindentation tests showed that the folia exhibit a hardness of about 3 GPa and elastic modulus of about 73 GPa. Microcracks were generated using a microindenter in order to study the fracture mechanisms of the folia. Following on from these investigations, fracture mechanisms are discussed in conjunction with the correlation between preferred orientation and structural characteristics during cracking of the folia. Comparing the morphology and the polymorphism with nacre (also known as mother of pearl), the advantages of the relatively fast crystal growth and less amount of organic matrix in folia may have interesting implications for the development of sophisticated synthetic materials.