Nonenzymatic Transformation of Amorphous CaCO3 into Calcium Phosphate Mineral after Exposure to Sodium Phosphate in Vitro: Implications for in Vivo Hydroxyapatite Bone Formation

Studies indicate that mammalian bone formation is initiated at calcium carbonate bioseeds, a process that is driven enzymatically by carbonic anhydrase (CA). We show that amorphous calcium carbonate (ACC) and bicarbonate (HCO₃^?) cause induction of expression of the CA in human osteogenic SaOS‐2 cells. The mineral deposits formed on the surface of the cells are rich in C, Ca and P. FTIR analysis revealed that ACC, vaterite, and aragonite, after exposure to phosphate, undergo transformation into calcium phosphate. This exchange was not seen for calcite. The changes to ACC, vaterite, and aragonite depended on the concentration of phosphate. The rate of incorporation of phosphate into ACC, vaterite, and aragonite, is significantly accelerated in the presence of a peptide rich in aspartic acid and glutamic acid. We propose that the initial CaCO₃ bioseed formation is driven by CA, and that the subsequent conversion to calcium phosphate/calcium hydroxyapatite (exchange of carbonate by phosphate) is a non‐enzymatic exchange process.     

Biomineralization of calcium carbonate by adding aspartic acid and lysozyme

Calcium carbonate is one of the most abundant materials present in nature. Crystal structures of CaCO₃ become three polymorphic modifications, namely calcite, aragonite and vaterite. Polymorphic modifications are mediated by adding aspartic acid (Asp) and lysozyme. Lysozyme, which is a major component of egg white proteins, has influenced the calcification of avian eggshells. The influence of Asp and lysozyme on the crystallization of CaCO₃ was investigated by adding these additives and calcium chloride solution into sodium carbonate solution in a crystallization vessel. CaCO₃ crystals were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared spectrometry (FT-IR). XRD was used to select the intensities and crystal structure of specific calcium carbonate. SEM was employed for the analysis of the morphology of the precipitation and particle size. Two kinds of crystals were identified by FT-IR spectrum. Hexagonal crystals of vaterite were affected by the Asp in the crystallization solution. However, rhombohedral crystals of calcite by lysozyme were formed without any sign of vaterite.     

Structural characteristics of poly(vinyl alcohol)–calcium carbonate composites prepared by sequential method

Abstract

Composites of poly(vinyl alcohol) (PVA) and calcium carbonate (CaCO₃) were prepared by a sequential method involving first in situ synthesis of CaCO₃ in PVA solution, then physical crosslinking of synthetic suspension and subsequently washing of resultant elastic gel followed by consolidation. The phase and composition, mechanical properties and microstructure of the composites and possible molecular interactions between both components were evaluated. X-ray diffraction analysis revealed that calcium carbonate was mainly composed of aragonite and calcite. Compression tests confirmed the composites prepared by this sequential method had good mechanical properties and that the compressive strength of the composites increased with higher content of calcium carbonate. PVA formed an interconnected network and needle-like CaCO₃ crystals together with some fine grains were well compatible with PVA. In situ synthesis induced a spectral shift of hydroxyl groups and C–O bonds of PVA and the suppression of the characteristic adsorption of calcite was also observed, according to Fourier transform infrared spectroscopy measurements.     

Calcium removal from industrial wastewater by bio‐catalytic CaCO3 precipitation

High concentrations of soluble calcium in industrial wastewater present problems due to the calcification of downstream processing. The current trend towards circuit closure and increased water re‐use will escalate this problem. We investigated ureolytic microbial carbonate precipitation as a novel process for removing excess calcium from industrial effluents. Two laboratory‐scale reactors, both with a hydraulic retention time of 8 h, were fed with 1.8 dm³ of anaerobic effluent (about 11 mM Ca²⁺) from a paper recycling plant. Both reactors were inoculated with pre‐cultivated calcareous sludge and the treatment reactor was additionally dosed with urea to a final concentration of 8.3 mM . Even though the anaerobic wastewater was saturated as such with respect to CaCO₃, urea addition and hydrolysis was shown to be a pre‐requisite for precipitation. Almost all (85–90% w/v) of the soluble calcium was precipitated as CaCO₃ and removed through sedimentation in the treatment reactor. This bio‐catalytic process presents an uncomplicated and efficient method for the removal of calcium from industrial wastewater. Copyright © 2003 Society of Chemical Industry     

Calcium carbonate inhibition by a phosphonate-terminated poly(maleic-co-sulfonate) polymeric inhibitor

The precipitation of calcium carbonate scale on heat transfer surfaces widely occurs in numerous industrial processes. For the control of calcium carbonate scale and in response to environmental guidelines, the new low phosphonic copolymer was prepared through reaction of maleic anhydride with sodium p-styrene sulfonate in water with redox system of hypophosphorous and hydrogen peroxide as initiator. The anti-scale property of the low phosphonic copolymer towards CaCO₃ in the artificial cooling water was studied through static scale inhibition tests, and the effect on formation of CaCO₃ was investigated with combination of scanning electronic microscopy (SEM), X-ray powder diffraction (XRD) analysis and Fourier transform infrared spectrometer, respectively. The results showed that the low phosphonic copolymer was excellent calcium carbonate scale inhibitor in artificial cooling water. The crystallization of CaCO₃ in the absence of inhibitor was rhombohedral calcite crystal, whereas a mixture of calcite with vaterite crystals was found in the presence of the low phosphonic copolymer. For actions of carboxyl and phosphonic acid groups, the calcite was inhibited and the metastable vaterite was stabilized in the presence of the low phosphonic copolymer during the CaCO₃ formation process.     

Synthesis of nanosized calcium carbonate (aragonite) via a polyacrylamide inducing process

A carbonation route for the synthesis of nanosized calcium carbonate (aragonite) was studied. In the process, polyacrylamide was used as an organic substrate to induce the nucleation and growth of calcium carbonate. The calcium carbonate particles were produced by means of carbonation of the mixture of calcium hydroxide and polyacrylamide by bubbling CO₂/N₂ gas mixture_. The operating parameters such as the concentration of organic substrate and temperature were varied to study their influences on the polymorph and crystal sizes of calcium carbonate particles. The morphology of the calcium carbonate particles was characterized with transmission electron micrograph (TEM). The synthesized calcium carbonate particles in the presence of organic substrate are the mixture of aragonite with needle shape and calcite with cubic shape. Fourier transform infrared spectroscopy (FTIR) analysis reveals the presence of aragonite and calcite. The polymorphs and their crystal sizes were characterized with X-ray diffraction (XRD). The calcium carbonate nucleated in the organic substrate exhibited different endothermic peak in differential thermal gravity (DTG) results compared to one coexisting with the organic substrate.     

Effect of Hydraulic Activity on Crystallization of Precipitated Calcium Carbonate (PCC) for Eco-Friendly Paper

Wt% of aragonite, a CaCO₃ polymorph, increased with higher hydraulic activity (°C) of limestone in precipitated calcium carbonate (PCC) from the lime-soda process (Ca(OH)₂-NaOH-Na₂CO₃). Only calcite, the most stable polymorph, was crystallized at hydraulic activity under 10 °C, whereas aragonite also started to crystallize over 10 °C. The crystallization of PCC is more dependent on the hydraulic activity of limestone than CaO content, a factor commonly used to classify limestone ores according to quality. The results could be effectively applied to the determination of polymorphs in synthetic PCC for eco-friendly paper manufacture.     

Influence of crystallization conditions on crystal morphology and size of CaCO3 and their effect on pressure filtration

The temperature, supersaturation, seeding procedure, stirring speed and other parameters were varied in crystallization experiments of calcium carbonate performed in aqueous solutions to control size, particle size distribution and morphology of the particles. Particle size information was obtained by focused beam reflectance measurements and the Coulter Counter Multisizer. Crystals of CaCO₃ could be crystallized as spherical polycrystalline particles of the vaterite polymorph, needle‐like crystals of aragonite and both cube‐like and novel plate‐like crystals of calcite. Filtration experiments for calcium carbonate, performed at a constant pressure difference of 2 bar, show that spherical particles with a larger size show better filterability and that spheres with a wider size distribution, as a result of high supersaturation and nucleation, give higher average cake resistance values. Comparing different particle morphologies, plate‐like crystals and needle‐like crystals show worse filterability than spherical particles and cube‐like particles. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Effect of Organic Additives on Electrochemical Surface Precipitation and Polymorphism of CaCO3

The inhibition effect of three organic additives on the precipitation and polymorphism of CaCO₃ deposited on gold surfaces was investigated using electrochemical and microscopic techniques. Additives, two polyacrylic acid (PAA) polymers with different molecular weights (Mw 2100, Mw 30,000), and 1,2,4,5‐benzenetetracarboxylic acid (BTCA), were either added to the solution before or during deposition. In the presence of 100 ppm of one of the three additives in solution, almost no scale was observed on the surface for at least 24 hours. In the presence of lower concentrations of PAA Mw 2100, only distorted calcite crystals were obtained while with PAA Mw 30,000 the polymorph was spherical vaterite. A mixture of calcite and vaterite was observed with the BTCA additive. Addition of the polymers inhibits further nucleation and growth even if added after partial deposition of CaCO₃ while BTCA has no effect once nucleation has started. The results indicate that the inhibit ion effect of the PAA polymers is due to adsorption on the electrode surface while the effect of BTCA is related to chelation of calcium ions in solution.     

pH‐dependent facile synthesis of CaAl‐layered double hydroxides and its effect on the growth inhibition of cancer cells

The present communication reports a pH‐dependent facile synthesis of calcium aluminum layered double hydroxide (CaAl‐LDH), at 3 different pH conditions of 8.5, 10.5 and 12.5 respectively, by simple coprecipitation route that led to the precipitation of the same in phase pure or in mixed phase form, and their detail characterization. Interestingly, at a pH of 8.5, the precipitate obtained was 100% phase pure CaAl‐LDH, represented as sample A, whereas, at higher pH conditions, a mixed phase comprising 37% of a combination of CaCO₃ polymorphs, e.g., calcite and aragonite and 63% of the CaAl‐LDH (at pH 10.5, represented as sample B) and 43% of a combination of calcite and aragonite and the rest 57% being CaAl‐LDH (at pH 12.5, represented as sample C) respectively, were obtained. The increasing trend of the presence of carbonate anion (with reference to calcite and aragonite phases) was estimated by trace level ion‐exchange chromatography study using organic acid column. All the above samples were tested for their anticancer activity in vitro, using cancer cell lines, e.g., human colon carcinoma (HCT116) and human breast adenocarcinoma (MCF7). Interestingly, sample A only exhibited significant growth inhibition of the cancer cells as above‐mentioned. The observation as above was verified using human osteoblast precursor cells (MC3T3) as well, on which, all the samples (sample A, sample B and sample C) exhibited good cellular viability.     

Synthetic Aragonite (CaCO3) as a Potential Additive in Calcium Phosphate Cements: Evaluation in Tris‐Free SBF at 37°C

Conventional SBF (simulated/synthetic body fluid) solutions are buffered at pH 7.4°C and 37°C using 50 mM Tris [(HOCH₂)₃CNH₂]. Tris is not present in human blood or metabolism and its high concentration makes it the third major component of SBF solutions. All three crystalline polymorphs of calcium carbonate (calcite, aragonite and vaterite) have never been tested simultaneously in an SBF solution. This study presents the SBF‐testing of the particles of these polymorphs at 37°C in Na‐L‐lactate (22 mM)‐buffered Lac‐SBF solution. While the calcite rhombohedra remained completely inert in the solution, vaterite spherulites and aragonite needles accrued apatitic CaP (calcium phosphate) deposits on their surfaces. Mg‐doped (1050 ppm) synthetic aragonite particles did not transform into calcite for 96 h in the Lac‐SBF solution while increasing their BET surface area by about 560% via the apatitic CaP deposits. Given the well‐established use of calcite powders in CaP cement formulations, synthetic aragonite particles may be a potential replacement for calcite due to their rapid response to blood plasma‐like solutions in between 24 and 48 h at 37°C.     

Linear-dendritic block copolymers as a green scale inhibitor for calcium carbonate in cooling water systems

Water-soluble monomer APEG-PG-(OH)n were produced and the Structure of APEG-PG-(OH)5 were identified by ¹H-NMR. APEG-PG-(OH)n were copolymerized with maleic anhydride (MA) to synthesize no phosphate and nitrogen free calcium carbonate inhibitor MA/APEG-PG-(OH)n. The structure and thermal property of MA/APEG-PG-(OH)5 were characterized and measured by ¹H-NMR, GPC and TGA. The observation shows that the dosage and n value of MA/APEG-PG-(OH)n plays an important role on CaCO₃ inhibition. MA/APEG-PG-(OH)5 displays superior ability to inhibit the precipitation of calcium carbonate, with approximately 97% inhibition at a level of 8 mg/L. The effect on formation of CaCO₃ was investigated with combination of SEM and XRD analysis.     

Effect of polyethylene glycol on phase and morphology of calcium carbonate

Calcium carbonate (CaCO₃) with different phases and morphologies were prepared and characterized by scanning electron microscopy (SEM), powder X‐ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. The effect of polyethylene glycol (PEG) with different molecular weight and concentrations on the phase and morphology of CaCO₃ was studied. The results showed that aragonite was the only phase in the solution without PEG, while calcite phase could be obtained by the use of PEG as the additive. The possible crystallization mechanism for the formation of CaCO₃ polymorphs in the presence of different PEG was also discussed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of acidic calcium phosphate concentration on mechanical strength of porous calcite fabricated by bridging with dicalcium phosphate dihydrate

Porous calcium carbonate (CaCO₃) has attracted attention as an artificial bone substitute. We previously reported that interconnected porous calcite block can be fabricated when calcite granules are exposed to acidic calcium phosphate (ACaP) under loading conditions. Dicalcium phosphate dihydrate (DCPD) formed on the surface of the calcite granules caused bridging of the calcite granules with one another and formed an interconnected porous calcite block with DCPD. In this study, the effect of the ACaP concentration on the mechanical strength of the interconnected porous calcite was studied under loading conditions. When the ACaP concentration was increased, the amount of DCPD increased and the compressive strength of the porous calcite increased to approximately 2 MPa. The interconnected porous structure was maintained regardless of the ACaP concentration. No statistically significant difference was observed for the porosity, which was approximately 50%, based on the concentration of ACaP. Therefore, we concluded that the amount of precipitated DCPD can be regulated by the concentration of ACaP solution, and the mechanical strength of the porous calcite can be regulated by the amount of the precipitated DCPD.     

Effects of magnetic field on calcium carbonate precipitation: Ionic and particle mechanisms

There are two most widely reported mechanisms to study the effect of magnetic fields on calcium carbonate (CaCO₃) precipitate, namely ionic and particle mechanisms. The effects are most debatable because they are contrary to each other. This study explored the effects of both mechanisms in CaCO₃ deposit and total CaCO₃ precipitation using ionic and particle methods. The ionic method showed reductions in CaCO₃ deposit and total precipitation rate of CaCO₃, whereas the particle method showed the opposite results. The particle number decreased and the average particle diameter of CaCO₃ deposit increased in the ionic method. Meanwhile in the particle method, the particle number increased, average particle diameter decreased and particle aggregation of CaCO₃ was observed. XRD measurement on all deposits showed that the crystal deposit was mostly of calcite and the traces of vaterite. However, the amount of the crystal in the particle method was observed to be less than that in the ionic method, indicating that CaCO₃ deposit was more amorphous. Particle mechanism decreased the Ca²⁺ ion concentration in solution during magnetization, and ionic mechanism reduced scale (CaCO₃) formation after magnetization and separation processes. This method could be applied for decreasing water hardness and prevent the formation of scaling.     

Membrane autopsy to investigate CaCO3 scale formation in pilot‐scale,submerged membrane bioreactor treating calcium‐rich wastewater

BACKGROUND: Membrane scaling is an area of research interest because it can deteriorate membrane performance. The extent to which membrane scaling is produced varies depending upon the concentration of scale‐forming species such as calcium on the membrane surface. Bench‐scale tests have been conducted to better understand membrane scaling in submerged membrane reactors (MBR). However, relatively few studies of membrane scaling in pilot‐scale, submerged MBR have been reported. The objective of this study was to perform membrane autopsy work to analyze membrane scaling in a submerged MBR treating calcium‐rich wastewater. RESULTS: Membrane autopsy work provided evidence that deposition of calcium carbonate (CaCO₃) scale occurred on the membrane surface at the completion of pilot‐scale, submerged MBR operation. The CaCO₃ scaling resulted in significant external fouling on the surface of the membrane. The membrane scaling increased the rejection of calcium with MF membranes. However, the level of CaCO₃ scaling as internal fouling (in the pores) was almost negligible. This autopsy work also showed that aeration did not play a major role in controlling CaCO₃ scaling at the membrane surface in a submerged MBR. Chemical cleaning using citric acid solution efficiently removed CaCO₃ scale from the membrane. Combining citric acid with sodium hypochlorite pretreatment provided synergistic effects, further reducing CaCO₃ scale formation. CONCLUSION: The carbonate salt of calcium leads to precipitation resulting in surface fouling of membranes, and this cannot be removed physically by aeration in a submerged MBR treating calcium‐rich wastewater. It is necessary to combine properly‐selected cleaning strategies with submerged MBR treating wastewater containing a high potential for inorganic chemical precipitates. Copyright © 2009 Society of Chemical Industry     

Efficiency of five scale inhibitors on calcium carbonate precipitation from hard water: Effect of temperature and concentration

The effects of temperature and concentration of five scale inhibitors (three polyphosphates, one polyphosphonate and one polycarboxylate) on calcium carbonate (CaCO₃) precipitation from hard water are reported in this paper. The CaCO₃ precipitation from calcocarbonically pure water was induced by imposed potential and studied on gold electrode by chronoamperometry technique. With this technique, the efficiency of preventing CaCO₃ precipitation was determined for all scale inhibitors. The composition of these scale inhibitors were analysed by ICP-AES technique and no or few toxic elements were detected. For each tested inhibitor, the optimal concentration was determined and their efficiency was studied in the range temperature 20-50 °C. SEM/EDS and Raman spectroscopy techniques were used to analyse the microstructure and the elemental composition of the formed scale. Only polyphosphonates remain efficient at 50 °C. All the tested inhibitors were shown to act by threshold effect.     

Epitaxial Relationships between Calcium Carbonate and Inorganic Substrates

The polymorph-selective crystallization of calcium carbonate has been studied in terms of epitaxial relationship between the inorganic substrates and the aragonite/calcite polymorphs with implication in bioinspired mineralization. EpiCalc software was employed to assess the previously published experimental results on two different groups of inorganic substrates: aragonitic carbonate crystals (SrCO₃, PbCO₃, and BaCO₃) and a hexagonal crystal family (α-Al₂O₃, α-SiO₂, and LiNbO₃). The maximum size of the overlayer (aragonite or calcite) was calculated for each substrate based on a threshold value of the dimensionless potential to estimate the relative nucleation preference of the polymorphs of calcium carbonate. The results were in good agreement with previous experimental observations, although stereochemical effects between the overlayer and substrate should be separately considered when existed. In assessing the polymorph-selective nucleation, the current method appeared to provide a better tool than the oversimplified mismatch parameters without invoking time-consuming molecular simulation\.     

The development and stability of surface layers on concrete exposed to sea-water

Concrete exposed to sea-water may develop a surface skin causing a marked reduction in permeability. The skin typically consists of a layer of brucite (magnesium hydroxide) of aroun 30 μm thickness, overlain by a thicker, but more slowly developing, layer of aragonite (calcium carbonate). The aragonite may convert to calcite in an aqueous environment free from magnesium ion.The degree of saturation of sea-water with aragonite or brucite is primarily a function of its pH value. Uncontaminated sea-water has a pH within the range 7.8 to 8.3 and is supersaturated with aragonite at pH values greater than around 8.1. For good correlation of laboratory tests with natural exposure conditions appreciable increases in pH should therefore be prevented. Temperature variations may have a significant effect on layer precipitation, but the range of pressures encountered by offshore structures has negligible effect. Organic compounds present in sea-water may inhibit precipitation.     

Effect of in situ deposition of calcium carbonate in cotton fiber on its mechanical properties

In this study, in order to improve mechanical properties of cotton fabrics, nano-micro sized calcium carbonate (CaCO₃) was deposited in situ on cotton fabrics. The mechanical properties, surface morphology, crystalline index, infrared spectrum, thermal property, and wettability of the deposited fabrics were measured and discussed. The results showed that the breaking strength of cotton fabric increased by about 10% after in situ deposition of nano-micro calcium carbonate. After ultrasonic washing, the strength of cotton fabric deposited CaCO₃ was still increased by about 10%. The crystallinity of the cotton fabric deposited with calcium carbonate increased from 76% to 84%. The hydrogen bond between cellulose molecules and calcium carbonate was confirmed by infrared spectroscopy. The hydrophilicity and thermal properties of cotton fabric were not significantly influenced by calcium carbonate deposition. This provides a new idea for improving the mechanical properties of cotton fabric.