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PubMed2001

Mechanochemical synthesis of nanocrystalline hydroxyapatite from CaO and CaHPO4.

Ceramic hydroxyapatite phase was triggered to occur by high-energy mechanical activation of a dry powder mixture of calcium oxide (CaO) and anhydrous calcium hydrogen phosphate (CaHPO4). A singe-phase hydroxyapatite of high crystallinity was realised by >20 h of mechanical activation without further thermal treatment at high temperatures. The resulting hydroxyapatite powder exhibits an average particle size of approximately 25 nm and a specific surface area of 76.06 m2/g, as measured by multi-point BET technique. It was sintered to a density of 98.20% theoretical density at 1200 degrees C for 2 h.

Calcium Compounds↗

PubMed2003

Surface modification of tricalcium phosphate for improvement of the interfacial compatibility with biodegradable polymers.

The surface of tricalcium phosphate (TCP) filler particles was activated by treatment with dilute aqueous phosphoric acid. ATR-IR spectra indicated the formation of calcium hydrogen phosphate dihydrate at the surface. Oligo(lactone)s were formed by the subsequent reaction of the activated TCP with L-lactide and epsilon -caprolactone, respectively, at 150 degrees C without any additional catalysts. After extraction of the oligo(lactide), the residue of modified TCP-included calcium lactate whereas the water of crystallization of the dihydrate disappeared as shown by ATR-IR spectroscopy. Owing to the insolubility of TCP in common solvents, the analogous reaction between water-soluble disodium hydrogen phosphate dihydrate and L-lactide was used to study the kind of chemical bonds by high-resolution NMR spectroscopy. The 1H and 13C NMR spectra of the reaction product also pointed out the presence of calcium lactate. Additionally, signals were found indicating a covalent attachment of lactic acid units onto the phosphorus. For the preparation of composites, poly(L,DL-lactide) was mixed with TCP and modified TCP, respectively, in a ratio of 75/25 (w/w) and directly injection moulded into tensile test specimens at a barrel temperature of 180 degrees C. Although mechanical properties were not improved, scanning electron microscopy (SEM) indicated a better interfacial phase interaction in the composite with the modified TCP. Chemical bonds between filler and polymer matrix are assumed to be formed by transesterification reactions.

Biocompatible Materials↗

PubMed1997

Bioeutectic: a new ceramic material for human bone replacement.

In the present work, a new way of obtaining bioactive ceramic materials with eutectic morphology is presented. To this purpose the binary system wollastonite-tricalcium phosphate was selected, taking into account the different bioactivity behaviour of both phases. The material is formed by quasi-spherical colonies composed of alternating radial lamellae of wollastonite and tricalcium phosphate. In in vitro experiments the material presents a high reactivity, with the formation of two well-differentiated zones of hydroxyapatite, one formed by alteration of the eutectic material with solution of the wollastonite into the simulated body fluid and subsequent pseudomorphic transformation of the tricalcium phosphate into hydroxyapatite, and the other, in the last stages of the experiments, by deposition of hydroxyapatite onto the surface of the material. The hydroxyapatite morphology, formed at the beginning of the reaction, is similar to that of porous bone. The method used opens the opportunity to develop a new family of bioactive materials with different constituents, binary or ternary, for which the authors propose the general name of bioeutectics.

Biocompatible Materials↗

PubMed1998

The response of peritoneal macrophages after implantation of several ceramics as measured by the change of ectoenzyme activity.

The bioactive calcium phosphate ceramics with various calcium: phosphorus ratios: Ca/P = 1.67 (hydroxyapatite, HA), Ca/P = 1.6 and Ca/P = 1.5 (tricalcium phosphate, beta-TCP), the bioinert aluminium oxide ceramic (Al2O3) and the toxic calcium oxide ceramic (CaO) have been investigated with respect to their ability to activate peritoneal macrophages of NMRI-mice and with respect to their influence on the extracellular nucleotide degradation of these macrophages. Two weeks after the intraperitoneal injection of a suspension of ceramic particles in an isotone salt solution (phosphate-buffered saline = PBS), we observed that the peritoneal macrophages were only slightly activated into the responsive state, independent of the type of ceramic. 5'Nucleotidase (5'N) ectoenzyme hydrolyses adenosine monophosphate (AMP) and a decrease of its activity is a general biochemical marker of activated macrophages. This ectoenzyme activity was slightly reduced after ceramic implantation. The lacking rise of the extracellular diadenosine tetraphosphate (Ap4A)-catabolism by the macrophage ectoenzyme alkaline phosphodiesterase I (APD) demonstrated that the peritoneal macrophages did not completely reach the responsive state. After the implantation of calcium phosphate ceramics the extracellular adenosine triphosphate (ATP)-reduction was slightly diminished. After the implantation of tricalcium phosphate ceramic about 30% more peritoneal exsudate cells (PEC) were obtained from the peritoneal cavity than after injections of pure PBS (used as non-inflammatory control). Similar to the phenomena following the injection of thioglycollate (Tg, inflammation producing control agent) a slightly but not significantly increased proportion of pseudopodia-building cells was observed after the implantation of the ceramic with Ca/P = 1.6.

5'-Nucleotidase↗

PubMed1999

Bioactive ceramics prepared by sintering and crystallization of calcium phosphate invert glasses.

Novel glass-ceramics were synthesized via sintering and crystallization by heating powder compacts of SiO2-free calcium phosphate invert glasses of 60CaO x 30P2O5 x 7Na2O x 3TiO2 or 60CaO x 30P2O5 x 7Na2O x 3MgO at 800-850 degrees C in air. The glass-ceramics were relatively dense materials consisting of crystalline phases such as beta-Ca3(PO4)2 and beta-Ca2P2O7 with glassy phases. The compacts were densified by the viscous flow of the glassy phases while heating. By soaking in simulated body fluid at 37 degrees C, a calcium phosphate phase was formed newly on the surface of the glass-ceramic derived from 60CaO x 30P2O5 x 7Na2O x 3TiO2 glass, while the phase was not formed on that derived from 60CaO x 30P2O5 x 7Na2O x 3MgO glass: the former was implied to show bioactivity. Composition of the glassy phase as the matrix varies with the additives such as TiO2 and MgO, and the chemical properties of the phase influence the bioactivity of the glass-ceramics. The glass-ceramic derived from 60CaO x 30P2O5 x 7Na2O x 3TiO2 glass has relatively high fracture toughness of K(IC) approximately 2 MPa m(0.5) and bending strength of 100-120 MPa.

Calcium Compounds↗

PubMed2002

Stabilization of phosphogypsum using class C fly ash and lime: assessment of the potential for marine applications.

Phosphogypsum (PG, CaSO(4).H(2)O), a solid byproduct of phosphoric acid manufacturing, contains low levels of radium ((266)Ra), resulting in stackpiling as the only currently allowable disposal/storage method. PG can be stabilized with class C fly ash and lime for potential use in marine environments. An augmented simplex centroid design with pseudo-components was used to select 10 PG:class C fly ash:lime compositions. The 43cm(3) blocks were fabricated and subjected to a field submergence test and 28 days saltwater dynamic leaching study. The dynamic leaching study yielded effective calcium diffusion coefficients (D(e)) ranging from 1.15 x 10(-13) to 3.14 x 10(-13)m(2)s(-1) and effective diffusion depths (X(c)) ranging from 14.7 to 4.3mm for 30 years life. The control composites exhibited diametrical expansions ranging from 2.3 to 17.1%, providing evidence of the extent of the rupture development due to ettringite formation. Scanning electron microscopy (SEM), microprobe analysis showed that the formation of a CaCO(3) on the composite surface could not protect the composites from saltwater intrusion because the ruptures developed throughout the composites were too great. When the PG:class C fly ash:lime composites were submerged, saltwater was able to intrude throughout the entire composite and dissolve the PG. The dissolution of the PG increased the concentration of sulfate ions that could react with calcium aluminum oxides in class C fly ash forming additional ettringite that accelerated rupture development. Effective diffusion coefficients and effective diffusion depths alone are not necessarily good indicators of the long-term survivability of PG:class C fly ash:lime composites. Development of the ruptures in the composites must be considered when the composites are used for aquatic applications.

Calcium Compounds↗

PubMed1996

Repair of furcal perforations with mineral trioxide aggregate: two case reports.

Furcal perforation is an unfortunate incident that can occur during root canal therapy or post preparation of multirooted teeth. Studies have shown that the materials currently used to repair these iatrogenic accidents are inadequate. The poor prognosis of furcation perforations is probably due to bacterial leakage or lack of biocompatibility of repair materials. On the basis of the recent physical and biologic property studies of the newly introduced mineral trioxide aggregate, this material may be suitable for closing the communication between the pulp chamber and the underlying periodontal tissues. These case reports support this hypothesis.

Adolescent↗

PubMed1999

Considerations in the selection of a root-end filling material.

Surgical root canal treatment often includes the placement of a root-end filling material. New materials have recently emerged to challenge the long-standing position of amalgam as the root-end filling material of choice. This review discusses several of the commonly used root-end filling materials, with emphasis on indications and contraindications for the use of each.

Aluminum Compounds↗

PubMed2001

Effects of quartz addition on the mechanochemical dechlorination of chlorobiphenyl by using CaO.

Grinding a mixture of 3-chlorobiphenyl (BP-Cl) and CaO with or without the addition of quartz was conducted in air by a planetary ball mill to investigate the mechanochemical dechlorination of BP-Cl. The dechlorinating reaction proceeds with an increase in grinding time, and over 99% of BP-Cl is decomposed at 360 min. Washing the ground sample with different solvents results in different products. Addition of quartz to the grinding mixture facilitates dechlorination efficiency, especially in the case of a high weight ratio of BP-Cl to CaO.

Biomechanical Phenomena↗

PubMed2002

A new process for converting SO2 to sulfur without generating secondary pollutants through reactions involving CaS and CaSO4.

Nonferrous smelters and coal gasification processes generate environmentally harmful sulfur dioxide streams, most of which are treated to produce sulfuric acid with the accompanying problems of market shortage and transportation difficulties. Some sulfur dioxide streams are scrubbed with an alkali solution or a solid substance such as limestone or dolomite, which in turn generates wastes that pose other pollution problems. While the conversion of sulfur dioxide to elemental sulfur has many environmental advantages, no processes exist that are environmentally acceptable and economically viable. A new method for converting sulfur dioxide to elemental sulfur by a cyclic process involving calcium sulfide and calcium sulfate without generating solid wastes has been developed. In this process, calcium sulfate pellets as the starting raw material are reduced by a suitable reducing agent such as hydrogen to produce calcium sulfide pellets, which are used to reduce sulfur dioxide producing elemental sulfur vapor and calcium sulfate. The latter is then reduced to regenerate calcium sulfide. Thermodynamic analysis and experimental results indicated that the CaS-SO2 reaction produces mainly sulfur vapor and solid calcium sulfate and that the gaseous product from the CaSO4-H2 reaction is mainly water vapor. The rates of the two reactions are reasonably rapid in the temperature range 1000-1100 K, and, importantly, the physical strengths and reactivities of the pellets are maintained largely unchanged up to the tenth cycle, the last cycle tested in this work. Sulfur dioxide-containing streams from certain sources, such as the regenerator off-gas from an integrated gasification combined cycle desulfurization unit and new sulfide smelting plants, contain much higher partial pressures of SO2. In these cases, the rate of the first reaction is expected to be proportionally higher than in the test conditions reported in this paper.

Air Pollutants↗

PubMed2005

Fate of endocrine-disruptor, pharmaceutical, and personal care product chemicals during simulated drinking water treatment processes.

The potential occurrence of endocrine-disrupting compounds (EDCs) as well as pharmaceuticals and personal care products (PPCPs) in drinking water supplies raises concern over the removal of these compounds by common drinking water treatment processes. Three drinking water supplies were spiked with 10 to 250 ng/L of 62 different EDC/ PPCPs; one model water containing an NOM isolate was spiked with 49 different EDC/PPCPs. Compounds were detected by LC/MS/MS or GC/MS/MS. These test waters were subjected to bench-scale experimentation to simulate individual treatment processes in a water treatment plant (WTP). Aluminum sulfate and ferric chloride coagulants or chemical lime softening removed some polyaromatic hydrocarbons (PAHs) but removed <25% of most other EDC/ PPCPs. Addition of 5 mg/L of powder activated carbon (PAC) with a 4-h contact time removed 50% to >98% of GC/ MS/MS compounds (more volatile) and 10% to >95% of LC/ MS/MS compounds (more polar); higher PAC dosages improved EDC/PPCP removal. EDC/PPCP percentage removal was independent of the initial compound concentration. Octanol-water partition coefficients served as a reasonable indicator of compound removal under controlled PAC test conditions, except for EDC/PPCPs that were protonated or deprotonated at the test pH and some that contained heterocyclic or aromatic nitrogen. Separate chlorine or ozone experiments decreased the EDC/PPCP initial concentration by <10% to >90%; EDC/PPCPs were likely transformed to oxidation byproducts. Ozone oxidized steroids containing phenolic moieties (estradiol, ethynylestradiol, or estrone) more efficiently than those without aromatic or phenolic moieties (androstenedione, progesterone, and testosterone). EDC/PPCP reactivity with oxidants were separated into three general groups: (1) compounds easily oxidized (>80% reacted) by chlorine are always oxidized at least as efficiently by ozone; (2) 6 of the -60 compounds (TCEP, BHC, chlordane, dieldrin, heptachlor epoxide, musk ketone) were poorly oxidized (<20% reacted) by chlorine or ozone; (3) compounds (24 of 60) reacting preferentially (higher removals) with ozone rather than chlorine. Conventional treatment (coagulation plus chlorination) would have low removal of many EDC/PPCPs, while addition of PAC and/or ozone could substantially improve their removals. Existing strategies that predict relative removals of herbicides, pesticides, and other organic pollutants by activated carbon or oxidation can be directly applied for the removal of many EDC/PPCPs, but these strategies need to be modified to account for charged (protonated bases or deprotonated acids) and aliphatic species. Some compounds (e.g., DEET, ibuprofen, gemfibrozil) had low removals unless ozonation was used. Other compounds had low removals by all the WTP processes considered (atrazine, iopromide, meprobamate, TCEP), and removal processes capable of removing these types of compounds should be investigated.

Alum Compounds↗

PubMed2005

Combustion properties and desulfurization of high sulfur containing Indian and Nepali coals using lime-based products.

Many brick industries and industrial boilers in South Asia use high sulfur containing coal as the major fuel. The combustion of these coals leads to serious environmental pollution and health problems. The SO2 emissions from the combustion of coal can be captured by adding lime-based desulfurizing agents (DSA) to the coal briquettes. The physical and combustion characteristics of some Indian (Bihar, Assam) and Nepali (Dang, Abidhara, Lignite) coal have been studied. The process of desulfurization of these coals was investigated using calcium hydroxide and calcium carbonate as DSA. Calcium carbonate is more efficient in char combustion than volatile combustion, whereas calcium hydroxide and sodium hydroxides are efficient as DSA in both char and volatile combustion. For most of the coals the desulfurization efficiencies are over 80% in case of Ca(OH)2 and NaOH for molar ratios of DSA to sulfur (Ca/S) of 2 and 3. For the same Ca/S ratios the desulfurization efficiency is about 75% when calcium carbonate is used. Use of calcium carbonate and calcium hydroxide as DSA in coal briquettes could be an efficient and economical way to control the pollution from the use of high sulfur containing coals used in brick industries in Nepal and South Asia.

Air Pollutants↗

PubMed2006

Solid-state NMR study of the transformation of octacalcium phosphate to hydroxyapatite: a mechanistic model for central dark line formation.

For many years, octacalcium phosphate (OCP) has been postulated as the precursor phase of biological apatite in bones and teeth. In this work, we study the molecular mechanism of OCP to hydroxyapatite (HAp) transformation in vitro by several physical techniques, with particular emphasis on solid-state (31)P homonuclear double-quantum (DQ) NMR spectroscopy. The in vitro system is prepared by mixing urea, sodium phosphate monobasic dehydrate, and calcium nitrate tetrahydrate at 100 degrees C. The images obtained by scanning electron microscopy and transmission electron microscopy show that the bladelike OCP crystals will transform into hexagonal rod-shaped HAp crystals as the pH of the reaction mixture increases slowly from 4.35 to 6.69 in 12 h. Powder X-ray diffraction patterns indicate that a trace amount of monetite was also precipitated when the pH was around 5. Together with computer-assisted lattice matching, our DQ NMR data reveal that OCP crystals transform to HAp topotaxially, where the [000](HAp) and [20](HAp) axes are along the same directions as the [001](OCP) and [010](OCP) axes, respectively. On the basis of our in vitro results, the formation of the central dark line commonly found in biological hard tissues could be explained by the inherent lattice mismatch between OCP and HAp. Furthermore, the data of the (31)P{(1)H} cross-polarization NMR suggest that water molecules enter the hydration layers of OCP crystals via the hydrolysis reaction HPO(4)(2)(-) + OH(-) = PO(4)(3)(-) + H(2)O, which also accounts for the deprotonation of the HPO(4)(2)(-) ions during the transformation.

Calcium Compounds↗

PubMed2006

Biocatalytic synthesis of a nanostructured and crystalline bimetallic perovskite-like barium oxofluorotitanate at low temperature.

Silicatein, an enzymatic biocatalyst from the marine sponge Tethya aurantia, is demonstrated to catalyze and template the hydrolysis/condensation of the molecular precursor BaTiF6 at low temperature to form nanocrystalline BaTiOF4, an orthorhombic oxofluorotitanate. The kinetics of hydrolysis and growth were studied in-situ via pH profiling and quartz crystal microbalance (QCM) techniques. The composition and structure of the resulting BaTiOF4 microstructures on the silicatein surface were characterized using FT-IR spectroscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction. The silicatein-mediated hydrolysis/condensation of BaTiF6 generates nanocrystalline BaTiOF4 (a high-temperature intermediate to BaTiO3) at 16 degrees C without any added acid or base, and the growth is templated along the protein filaments into floret microstructures. The unique combination of silicatein and the single-source molecular precursor has allowed a multimetallic perovskite-like material to be biocatalytically synthesized, in vitro, for the first time.

Barium Compounds↗

PubMed2002

Calcium absorption from three salts and CaSO(4)-fortified bread in premenopausal women.

Two studies were conducted to measure calcium absorption from calcium sulfate fortified bread and three salts (calcium lactate, calcium carbonate, and calcium sulfate) in healthy premenopausal women using a crossover design. In study I, calcium fractional absorption levels from the three salts labeled with a stable isotope, 44Ca, were not significantly different (0.039-0.47) as determined by the fecal recovery method. In a second study, absorption of 45Ca from CaSO(4)-fortified labeled bread or labeled milk was measured in serum exactly 5 h postingestion. Fractional calcium absorption was slightly but significantly greater from fortified bread than from milk (mean within subject difference = 0.0675 +/- 0.016). Calcium sulfate is a bioavailable fortificant for white bread that compares favorably with milk and two other salts.

Adsorption↗

PubMed2004

Evaluation of osteoblast-like cell response to Proroot MTA (mineral trioxide aggregate) cement.

Some endodontic sealers have been shown to cause local and systemic effects, mainly due to microleakage of chemicals from the sealer. To avoid the risk of toxic effects in vivo, the biological compatibility of filling materials has to be assessed. In vitro compatibility of Proroot MTA cement in comparison with two different fillers used in clinical practice, was examined by testing the adherence, viability, proliferation and secretion of collagen of osteoblast-like cells. In our experimental system, Saos-2 cells challenged with Proroot MTA for 24 and 72 h showed a better behaviour than the cells exposed to the other compounds under assay. We found that the cells attached to the rough surface of Proroot MTA cement and spread onto the rough surface. Moreover, the cells on Proroot MTA were viable, grew, and released some collagen even at 72 h, while cell metabolism and growth was dramatically reduced onto sEBA and amalgam surfaces. A parallel behaviour was found after the cells were challenged with extracts of the different fillers. In conclusion, according to our in vitro study, Proroot MTA showed a good interaction with bone-forming cells: such behaviour may partially account for its satisfying clinical performance.

Aluminum Compounds↗

PubMed2004

Pre-mineralisation of starch/polycrapolactone bone tissue engineering scaffolds by a calcium-silicate-based process.

This work describes a new methodology to produce bioactive coatings on the surface of starch-based biodegradable polymers or other degradable polymeric biomaterials. As an alternative to the more typical bioactive glass precursors, a calcium silicate gel is being employed as a nucleating agent, for inducing the biomimetic formation of a calcium-phosphate (Ca-P) layer. The method has the advantage of being able to coat efficiently both compact materials and porous 3-D architectures aimed at being used on tissue replacement applications and as bone tissue engineering scaffolds. This treatment is also very effective in reducing the incubation periods, being possible to observe the formation of an apatite-like layer, only after 12 h of immersion in a simulated body fluid (SBF). The apatite coatings formed on the compact surfaces or along the fibres of a fibre mesh scaffold structure made from a starch/polycrapolactone blend (SPCL) were analysed and compared in terms of morphology, chemical composition and structure. After the first days of SBF immersion, the apatite-like films exhibit the typical cauliflower like morphology. With increasing immersion times, these films exhibited a partially amorphous nature and the Ca/P ratios became very closer to the value attributed to hydroxyapatite (1.67). It was possible to fully pre-mineralise the SPCL scaffolds and simultaneously to keep the porous morphology of the fibre-bonded scaffold.

Absorption↗

PubMed2004

Apatite-forming ability of alginate fibers treated with calcium hydroxide solution.

Calcium alginate fibers were prepared by extruding an aqueous sodium alginate solution into an aqueous calcium chloride solution. The fibers were treated with a saturated aqueous calcium hydroxide solution for various periods and their apatite-forming ability was examined in a simulated body fluid (SBF). The calcium alginate fibers were treated with the aqueous calcium hydroxide solution for periods longer than five days formed apatite on their surfaces in SBF, and their apatite-forming ability improved with increasing calcium hydroxide treatment time. The amount of calcium ions released from the fibers also increased with increasing calcium hydroxide treatment time, resulting in acceleration of nucleation and growth of apatite on the fiber surfaces. The resultant apatite-alginate fiber composite is expected to be useful as a flexible bioactive bone-repairing material.

Alginates↗