Amorphous Calcium Research Articles

Aragonite and Its Composites: Preparations, Properties and Applications

AbstractAragonite, a metastable crystal form of calcium carbonate, exhibits the highest density and hardness among all species. Diversified forms of aragonite composites can be produced through different preparation processes, forming a relatively complete system in various application fields. Their properties and applications are determined by their multiple levels of structures and shapes. However, research information for aragonite‐related fields is currently lacking integration and clarification. This review provides a comprehensive overview on the preparation methods, properties, and potential applications of three main aragonite‐based materials: aragonite particles, nacre‐inspired mineralized aragonite composites (NMACs), and shell‐derived aragonite nanoparticles (SANPs). The formation mechanisms and versatile applications of these materials are thoroughly surveyed based on their initial precursor, reaction conditions, product forms including filler of aragonite whiskers synthesized by carbonation reaction; functional materials of NMACs fabricated by amorphous calcium carbonate‐organic matter (ACC‐OM) mediated process; biomedical materials of SANPs derived from aragonite cockle shells. Overall, this review aims to provide assistance for customized production of aragonite‐based materials as well as new research directions for both pure aragonites and its composites.

Application of various microscopy techniques to study early-age and longer-term behaviour of super sulphated cement microstructure.

Super sulphated cement (SSC) is a very promising substitute for traditional construction materials (i.e. Portland cement), due to its enhanced durability and particularly low environmental impact. This paper explores the microstructure and certain properties of SSC, focusing on the particular complexities of its microstructure and the difficulties of microanalysis of its hydrates. To do so, SSC paste samples were first cast to identify hydration products using X-ray diffraction, then observed at early age using confocal laser scanning microscopy (CLSM) and at early and late age using scanning electron microscopy. In addition, concrete cores impregnated with fluorescein in order to highlight porosity, cracking and aggregates debonding were observed under UV light using optical microscopy (OM), showing a complete absence of cracking and aggregate debonding. Both microscopy techniques (CLSM and UV light OM) have been applied to this type of binder for the first time. The results show that SSC microstructure is characterised by a sophisticated intergrowth of various phases, including ettringite and amorphous calcium-(alumina)-silicate hydrate gels. Finally, Monte-Carlo simulation of electron-matter has been provided for a better understanding of EDS analysis.

Preclinical evaluation of the degradation kinetics of third-generation resorbable magnesium scaffolds.

The novel sirolimus-eluting resorbable scaffold DREAMS 3G was designed as a third-generation development of its predecessor, the Magmaris scaffold. This preclinical study aimed to examine the qualitative and temporal course of the degradation of the DREAMS 3G relative to the Magmaris scaffold. Forty-nine DREAMS 3G and 24 Magmaris scaffolds were implanted into 48 mini swine for degradation kinetics analysis. Another DREAMS 3G was implanted into one mini swine for crystallinity analysis of the degradation end product after 730 days. Degradation kinetics were determined at 28, 90, 120, 180, and 365 days. Discontinuity density in DREAMS 3G was significantly lower than that in Magmaris scaffolds for the follow-up timepoints of 90 and 120 days. Planimetric analysis indicated 99.6% backbone degradation for DREAMS 3G at 12 months. Compared to the Magmaris scaffold, individual strut degradation in DREAMS 3G showed less variability and the remaining backbone core was more homogeneous. The degradation end product of DREAMS 3G manifested as calcium phosphate with a minor share of aluminium phosphate. DREAMS 3G showed almost complete degradation after one year, with amorphous calcium and aluminium phosphate as the end products of degradation. Despite its thinner struts, scaffold discontinuity was significantly lower in the DREAMS 3G than in the Magmaris scaffold, likely providing a longer scaffolding time.

Idiopathic calcinosis cutis with unusual histomorphology and negative von Kossa stain: A diagnostic pitfall

Introduction: Calcinosis cutis is characterized by basophilic crystalline or amorphous calcium within the dermis/subcutis. Calcinosis cutis has many different clinical subtypes and associated etiologies that may lead clinicians to consider this diagnosis. Von Kossa and/or Alizarin red special stains may be used by pathologists to highlight deposition of insoluble calcium salts, especially in histologically ambiguous or subtle cases. Case Report: We report the case of a 27-year-old male who presented with an inferior right buttock mass clinically diagnosed as epidermal inclusion cyst(s). Gross pathology revealed a gray-white pasty substance within a cyst-like structure. Histopathologic examination demonstrated pools of amorphous blue-gray material with rare deposits of admixed coarse calcifications surrounded by foreign-body giant cells. No cyst wall was seen in the specimen. Special stains, including von Kossa, were initially negative. Following additional review, it was discovered that surface decalcifying solution had been applied to the paraffin block in the histology lab prior to microtome sectioning. Hypothesizing that this could be the cause of the unusual morphology, the paraffin block was reprocessed and subsequent H and E stained sections displayed characteristic basophilic calcium deposits, which were correspondingly positive by von Kossa stain. Conclusion: The histopathologic diagnosis of calcinosis cutis is apparent by HandE in most cases, though von Kossa and/or Alizarin red special stains can be used to aid the pathologist. Given the unusual histomorphology following surface decalcification and initial lack of von Kossa stain prior to reprocessing, this report serves to make pathologists aware of this potential diagnostic pitfall.

3D biocompatible bone engineering foams with tunable mechanical properties and porous structures

AbstractLarge bone defects due to accidental injuries and fractures as well as the mismatch between the implant material and the defect site are major problems in biomedicine. Bone tissue engineering offers a solution to this problem. In this paper, a series of three‐dimensional porous composite scaffolds with shape memory were prepared using polycaprolactone and polytetrahydrofuran as soft segment materials, hexamethylene diisocyanate as hard segment materials and amorphous calcium phosphate/calcium citrate (CAP) as inorganic fillers. The scaffolds have tunable mechanical properties, melt temperature, surface wettability, a pore size range of 100–800 μm and a high degree of connectivity. In vitro mineralization showed good mineral deposition and energy dispersion spectrometer displayed uniform distribution of Ca and P elements on the surface. The composite scaffold exhibited good shape memory properties at 37°C. The shape fixation rate (Rf) and shape recovery rate (Rr) were maintained at 94.1% and 94.4% after five compression cycles. The resulting scaffold promoted MG63 cell proliferation to some extent. The scaffold is expected to be used clinically for the treatment of large bone defects.

Evaluation of the effects of different remineralisation agents on initial enamel lesions by scanning electron microscope and energy-distributed X-ray analysis.

This study compared the ability of four remineralization agents to restore demineralised enamel lesions in permanent human incisors. In total, 40 teeth were included in the study. Two samples were obtained from each tooth. The 80 samples were divided into 10 groups (n=8 per group). The right halves of the teeth were controls solely subjected to demineralisation and stored in artificial saliva for the duration of the experiment. The left halves of the teeth were remineralised using a 5% NaF-containing fluoride varnish (GC MI varnish; GC Corp.), a toothpaste containing casein phosphopeptide and amorphous calcium (GC tooth mousse; GC Corp.), a water-soluble remineralisation paste containing fluoride, hydroxyapatite, xylitol (Remin Pro; Voco), and ROCS remineralising gel containing Ca, magnesium(Mg) and phosphate (P). After 21days of remineralisation, scanning electron microscopy and energy-dispersive X-ray (EDX) assessments were performed, and the results were analysed using one-way analysis of variance. EDX analysis showed that the ROCS medical remineralising gel had the lowest Ca/P ratio among the groups (P = .04). Compared with the control groups, the Remin Pro and ROCS medical remineralising gel treatments produced significantly higher Ca/P ratios (P=.014 and P=.025). These results were statistically significant, and P-value <.05 was accepted for statistical significance. The group treated with a fluoride-free, xylitol-containing ROCS medical remineralising gel had the lowest Ca/P ratio. Compared with the control groups, Remin Pro and ROCS remineralising gel appeared effective for repairing initial enamel lesions.

Plasma ion implantation of 3D‐printed PEEK creates optimal host conditions for bone ongrowth and mineralisation

AbstractPolyether ether ketone (PEEK) is a three‐dimensional (3D)‐printable material with excellent mechanical properties for bone replacement implants. However, bioactivation is needed to improve its osseointegration. Plasma immersion ion implantation (PIII) provides PEEK surfaces with a high density of radicals, improving hydrophilicity and enabling covalent bonds with biological molecules. On the PIII‐treated surface, amorphous calcium phosphate‐associated protein depositions form a strongly bonded, mineralised layer during incubation in a cell culture medium. The strong adhesion is attributed to covalent linking of protein to the PEEK surface, which cannot be achieved by improved hydrophilicity or the introduction of functional groups alone. After 3D‐printed porous PEEK scaffolds were PIII‐treated, osteoblast‐like cell attachment increased by 8.8%, proliferation rate increased by 27% and mineralisation was enhanced, encouraging rapid osseointegration of patient‐specific implants.

Influence of shotcrete accelerators on the hydration of cement pastes and their impact on sulfate resistance

Alkali-free, aluminium-based accelerators are often used for shotcrete linings in tunnels and mines, where external sulfate attack can occur. Therefore, it is essential to know, if the influence of the accelerators on the cement hydrate assemblage negatively impacts sulfate resistance. This study focuses on the effect of aluminium-based accelerators on cement hydration and the consequences for external sulfate attack. Aluminum sulfate-based accelerators cause rapid setting due to the very early formation of ettringite and accelerate alite hydration. At late ages, significant more AFm phases are formed compared to the reference without accelerator, which during storage in sodium sulfate solution react to ettringite. A significantly higher volume increase due to the formation of additional ettringite during sulfate exposure was calculated by thermodynamic modelling for the accelerated paste compared to the reference. Alkaline accelerators based on sodium aluminate form mainly amorphous calcium (sulfo-) aluminate hydrates at very early age, while ettringite seems to be destabilized. The ettringite quantities formed during storage in sodium sulfate solution are significantly higher than for the reference and the paste with the alkali-free accelerator. This finding compares well to experiments on concrete specimens, where in the mixture with the alkaline accelerator deleterious expansion was observed.

Influence of Calcium/Silica Ratio on the Formation Belite Cement Clinker from Geothermal Sludges

Cement industry is seeking alternative raw material and process to reduce the energy consumption and environmental impacts from conventional cement manufacture. This paper describes process of belite cements synthesis. Geothermal sludges, an undesired waste from Dieng Geothermal Power Plant as amorphous silica source and calcium hydroxide were used to form belite cement at elevated temperatures. Experimental results showed that principal phase of belite cement (larnite or β-Ca2SiO4) was formed at temperature as low as 800 °C. Thus, the geothermal silica is shown to be very promising starting material for the low-temperature production of belite cement.

Bioinspired enhancement of chitosan nanocomposite films via Mg-ACC crystallization, their robust, hydrophobic and biocompatible

Amorphous calcium carbonate/chitosan (ACC/CS) nanocomposite films containing Mg-ACC (0–100 wt%) are prepared by simple natural evaporation-induced assembly. The influence of Mg-ACC content on the mechanical properties as well as cross-section of ACC-CS nanocomposite films were systematically investigated. The nanocomposite films exhibit an excellent mechanical property at Mg-ACC contents of 80 wt% compared to ordinary calcium carbonate/chitosan composites. With content of Mg-ACC increasing, the mechanical properties of ACC-CS nanocomposite films were further increased, reaching a maximum when the content of Mg-ACC to 80 wt%. Strength and Young's modulus of the 80 wt% ACC-CS nanocomposite film reach 121.67 MPa and 31.96 GPa, respectively, which is 2.3 and 5.1 times higher than that of the pure CS film. After undergoing Mg-ACC crystal transformation when the Mg-ACC content is greater than 80 wt%, the smooth structure was transformed into crystal-like agglomerates, which deteriorates mechanical properties. Furthermore, the as-prepared nanocomposite films show excellent hydrophobicity and high biocompatibilities for boosting the growth of Cell-293T. In addition, we also proposed a physical model for the dispersion of Mg-ACC in CS matrix, which could better explain the enhancement of the mechanical properties of nanocomposite films. The above results provide a comprehensive understanding of the development of high-performance bionic nanocomposites loaded with high nanofillers.

Effect of mineral reaction between calcium and aluminosilicate on heavy metal behavior during sludge incineration

Calcium-based additives such as lime, portlandite and limestone are widely applied in solid waste incineration for desulfurization. However, calcium may affect emission of heavy metals. In this study, effects of mineral reaction on the transference of copper and zinc during sludge combustion are investigated. Sludge from a chemical fiber factory was blended with lime as an additive in different mass fractions. The incineration tests were performed in a tube furnace at temperatures of 600–1100 °C. Then the ash was digested into two methods to clarify two retention forms of heavy metals. The X-ray diffraction shows that the calcium from additive converted to calcite, amorphous calcium, gehlenite and anorthite successively as temperature rising. The two-step digestion reveals that minerals above change the distribution of heavy metals between different forms. The residual form of both two heavy metals increases with temperature upgraded, while the leachable form presents an opposite trend. Calcium stimulated the volatility of copper at all temperatures but took positive effect on volatility of zinc only at 600 °C and promoted its retention at higher temperatures. With consideration of retention forms, mineral composition and temperature, it is suggested that through reactions with aluminosilicate, calcium changes heavy metals transference to a different extent. Competition by calcium to produce aluminosilicate inhibits retention of heavy metals, but zinc can be together with calcium as eutectic aluminosilicate at higher temperatures. Surface morphologies were detected by scanning electronic microscopy and energy dispersive spectrometer, confirming the effect of calcium.

Development and Characterization of a Novel Amorphous Calcium Phosphate/Multi (Amino Acid) Copolymer Composite for Bone Repair

Development and Characterization of a Novel Amorphous Calcium Phosphate/Multi (Amino Acid) Copolymer Composite for Bone Repair

Cryopellets based on amorphous organic calcium salts: Production, characterization and their usage in coagulation diagnostics

Abstract This work deals with the production and characterization of powders of amorphous organic calcium salts (excipients) as a possible recalcification source for citrated whole blood samples. Rapidly dissolving cryopellets were also prepared from these excipients. The amorphous excipients show high oversaturation which allows the manufacture of cryopellets containing a high amount of organic calcium salt. The characterization of the cryopellets revealed very rapid dissolution and breaking forces sufficient to withstand substantial mechanical stresses. Of the various individual and compounded excipients examined, calcium lactogluconate and calcium lactobionate are the best alternatives to CaCl2 for recalcification of citrated whole blood. Their influence on coagulation was minimal and both substances showed a low hygroscopic tendency during dynamic vapor sorption. Both excipients are non-hygroscopic under ambient conditions up to a relative humidity of p/p0 = 60%.

Fabrication of hydroxyapatite on pure titanium by micro-arc oxidation coupled with microwave-hydrothermal treatment

Porous hydroxyapatite (HA)-containing composite films were prepared by a novel method consisting of micro-arc oxidation (MAO) combined with microwave-hydrothermal (M-H) treatment. The morphology, composition and phase composition of the bioactive films were investigated with scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction. MTT assay was carried out to investigate the in vitro effects of the different surfaces on bone integration properties. The prepared MAO films consisted mainly of anatase, rutile and tricalcium phosphate along with amorphous calcium (Ca) and phosphorus (P) phases. The M-H-treated composite films were composed primarily of anatase, rutile and HA. As the time and temperature of the M-H treatment increased, the number of HA crystals gradually increased. Using the M-H method, HA was obtained at a lower temperature and in a shorter period of time compared to the conventional hydrothermal method. The results suggest that the M-H method significantly decreases the hydrothermal reaction temperature and also greatly shortens the reaction time. Due to the nanocrystallinity and porosity of the prepared composite films, the method presented here shows promise for the formation of bioactive materials for medical applications.

Histopathology of Embolic Debris Captured During Transcatheter Aortic Valve Replacement

Recent transcatheter aortic valve replacement studies have raised concerns about adverse cerebrovascular events. The etiopathology of the embolized material is currently unknown. A total of 40 patients underwent transcatheter aortic valve replacement with the use of a dual filter-based embolic protection device (Montage Dual Filter System, Claret Medical, Inc). Macroscopic material liberated during the transcatheter aortic valve replacement procedure was captured in the device filter baskets in 30 (75%) patients and sent for histopathologic analysis. The captured material varied in size from 0.15 to 4.0 mm. Amorphous calcified material (size, 0.55-1.8 mm) was identified in 5 patients (17%). In 8 patients (27%), the captured material (size, 0.25-4.0 mm) contained valve tissue composed of loose connective tissue (collagen and elastic fibers) with focal areas of myxoid stroma, with or without coverage by endothelial cells and intermixed with fibrin. In another 13 (43%) patients, collagenous tissue, which may represent elements of vessel wall and valvelike structures, was identified. In 9 patients (30%), thrombotic material was intermixed with neutrophils (size, 0.15-2.0 mm). Overall, thrombotic material was found in 52% of patients, and tissue fragments compatible with aortic valve leaflet or aortic wall origin were found in 52% (21/40) of patients. Embolic debris traveling to the brain was captured in 75% of transcatheter aortic valve replacement procedures where a filter-based embolic protection device was used. The debris consisted of fibrin, or amorphous calcium and connective tissue derived most likely from either the native aortic valve leaflets or aortic wall.

Soft chemistry synthesis, crystal structure and 3D-AFM-micro-structural surface features of calcium-barium selenate molecule with AB2X5 structure

Acetate-citrate precursors were applied to synthesize amorphous gelatinous calcium barium selenate with molecular formula (Ca0.5Ba0.5Se2O5). The gel-product was sintering at 800°C for 2 hrs then well characterized by X-ray diffraction, SEM and EDX elemental analyses and proved that the product Ca0.5Ba0.5Se2O5 is mainly belong to AB2X5-type structure with average grain size ranged in between 1.2–3.8 μm. A visualized study was constructed depending upon SEM and 3D-AFM experimental data to confirm the the microstructure morphological features of calcium-barium selenate surface.

Influence of Sn on the hydration of tricalcium aluminate, Ca3Al2O6

Tricalcium aluminate (Ca3Al2O6, C3A) containing 0–5% of Sn was synthesized by solid-state method, and the products were characterized by XRD technique. Differential thermo-analytical technique (DTA) along with X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) were applied to study the hydration behaviour of different C3A samples with and without the presence of gypsum. Results indicate that C3A can accommodate small amount of Sn in its structure and remaining amount forms SnO2. Hydration studies of the synthesized C3A shows that the additions of 0.5 and 1% Sn increase and 2% Sn decrease the reactivity of C3A at the initial period (<3 h) of hydration. Increasing additions of Sn also increase the amounts of amorphous phases and hexagonal calcium aluminate hydrates in the cement pastes. The stabilities of these hydration products also increase with increasing content of Sn in C3A at the experimental conditions. The presence of Sn significantly changes the hydration of C3A and gypsum solid mixture at the initial period of hydration by enhancing the formation of more amounts of AFt and AFm phases. However, at the later stage of hydration (on or after 3 days), the hydration products in C3A and gypsum pastes with and without the presence of Sn are almost similar.

State of water in amorphous calcium and calcium-magnesium phosphates

Fourier-transform infrared spectra of three samples of deposited amorphous phosphates, calcium monodiphosphate (orthopyrophosphate) with a molar ratio 2P/(2P + 1P) of ∼0.3, calcium magnesium monophosphate with an atomic ratio Mg/(Mg + Ca) of ∼0.3, and calcium-magnesium monodiphosphate with a molar ratio 2P/(2P + 1P) of ∼0.1 and atomic ratio Mg/(Mg + Ca) of ∼0.1, were analyzed. On the basis of the observed similarity between the v(OH), δ(OH) and (δ + ω)(OH) lines in the spectra of these phosphates and liquid water analogous states of water molecules therein were assumed. It was presumed that the formation of amorphous phosphates involves deposition of poorly soluble substances on the surface of water nanoclusters.

Calcium aluminate cements in fly ash/calcium aluminate blend phosphate cement systems: Their role in inhibiting carbonation and acid corrosion at a low hydrothermal temperature of 90°C

Study was focused upon formulating sodium polyphosphate-modified fly ash/calcium aluminate blend (SFCB) geothermal well cements with advanced anti-carbonation and anti-acid corrosive properties. At a low hydrothermal temperature of 90°C, to improve these properties, we investigated the effectiveness of various calcium aluminate cement (CAC) reactants in minimizing the rate of carbonation and in abating the attack of H2SO4 (pH ∼ 1.6). We found that the most effective CAC had two major phases, monocalcium aluminate (CA) and calcium bialuminate (CA2), and a moderate CaO/Al2O3 ratio of 0.4. The reaction between sodium polyphosphate (NaP) and CA or CA2 at room temperature led to the formation of amorphous dibasic calcium phosphate hydrate and anionic aluminum hydroxide caused by the decalcification of CA and CA2. When SFCB cement made with this CAC was exposed to 4% NaHCO3-laden water at 90°C, some carbonation of the cement occurred, forming calcite that was susceptible to the reaction with H2SO4. This reaction resulted in the deposition of gypsum gel scales as the acid corrosion product on the cement surfaces. The scale layer clinging to the cement protected it from further corrosion. Under such protection, the amorphous dibasic calcium phosphate hydrate → crystal hydroxyapatite and anionic aluminum hydroxide → crystal boehmite phase transitions were completed in acid solution. Meanwhile, the further chemical and hydration reactions of NaP with fly ash led to the formation of additional crystalline Na-P type zeolite phases. Thus, we propose that passivation of the surface of the cement by deposition of gypsum, following the formation of these reaction products, which are relatively inert to acid, are the acid corrosion-inhibiting mechanisms of the SFCB cements.

Biodegradation Study of Amorphous and Crystalline Calcium Metaphosphate in the SBF and Tris-Buffer Solution

Two types of pure and Na{sub 2}O added calcium metaphosphate (CMP), amorphous and crystalline, were prepared by the quenching from the melt and the crystallization of the amorphous CMP, respectively. Two specimens were soaked into tris-buffer solution and SBF for 1 day to 3 weeks. The weight decrease of the amorphous specimens was significantly higher than that of the crystalline specimens with the soaking time in the both solutions. The addition of Na{sub 2}O in CMP effects the weight change in the amorphous CMP, but not significant in crystalline CMP. And the addition of Na{sub 2}O in CMP also changes the deposition of calcium phosphate minerals, which is related to the dissolution of the CMP materials. The degradation and deposition was faster in the SBF than the tris-buffer solution. (orig.)