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PubMed2005

Manipulation of nanoneedle and nanosphere apatite/poly(acrylic acid) nanocomposites.

Colloidal apatitic nanosphere of 2-5 nm in diameter was synthesized in the presence of poly(acrylic acid), PAA. PAA, which has long been recognized as an inhibitor in the synthesis of hydroxyapatite, is used as a structure-directing agent for the synthesis of calcium-deficient apatite (CDHA) in this study. Experimental observation suggests a critical amount of the low-molecular-weight PAA, above which morphological evolution of CDHA nanoparticles from needle to sphere was observed. This reveals that the PAA acts as an inhibitor for the growth of CDHA crystals. Further incorporation of PAA of high molecular weight formed a highly optically transparent nanocomposite, even with the nanospherical apatite loading up to 35 wt %, suggesting no agglomeration. This was further justified through transmission electron microscopy (TEM), where the CDHA nanospheres were uniformly distributed in the PAA-CDHA nanocomposites. No interfacial crevices were visually observed, indicating a highly compatible interface between the inorganic CDHA and organic PAA phase.

Acrylic Resins↗

PubMed2007

CO2 laser-induced zonation in dental enamel: a Raman and IR microspectroscopic study.

The gradient of structural alteration and molecular exchange across CO(2) laser-irradiated areas in dental enamel was analyzed by Raman and attenuated total reflectance infrared microspectroscopy. The type and the degree of structural changes in morphologically distinguishable zones within the laser spot vary depending on the laser-irradiation parameters--power (1 and 3 W), treatment time (5 and 10 s), and operational mode (super pulse and continuous wave). Using higher power, irrespective of the operation mode, the enamel tissue ablates and a crater is formed. The prevalent phase at the bottom of the crater is dehydrated O(2) (2-)-bearing apatite, that is, the fundamental framework topology is preserved. Additional nonapatite calcium phosphate phases are located mainly at the slope of the laser crater. No structural transformation of mineral component was detected aside the crater rim, only a CO(3)-CO(2) exchange, which decays with the radial distance. A lower-power laser irradiation slightly roughens the enamel surface and the structural modification of enamel apatite is considerably weaker for continuous wave than for super pulse mode. Prolonged low-power laser treatment results in recrystallization, and thus structural recovering of apatite might be of clinical relevance for enamel surface treatments.

Apatites↗

PubMed1987

An ultrastructural study of calcium phosphate formation in multilamellar liposome suspensions.

Calcium phosphate precipitation can be induced within liposomes containing buffered inorganic phosphate by the ionophore-mediated loading of calcium ions. Negative staining, positive staining for thin sectioning, and freeze-fracture electron microscopy were used to characterize these synthetic vesicles and to evaluate the liposome-mineral interactions resulting from apatite formation. Suspensions of phosphate (0-50 mM KH2PO4)-encapsulated liposomes were prepared from mixtures of phosphatidylcholine, dicetyl phosphate, and cholesterol in the molar ratios of 7:2:1. Precipitation reactions were initiated by first suspending the liposomes in a buffered solution containing calcium (1.3-2.2 mM Ca(NO3)2) and then adding the cationic ionophore X-537A. All experiments were carried out at 22 degrees C, pH 7.4, and 240 mosm. Transmission electron microscopical analysis showed that the liposome preparation consisted of multilamellar, multicompartmental vesicular structures. The liposomes were typically heterogeneous with respect to both the size and number of phospholipid bilayers surrounding the aqueous cores. In Ca-loaded liposomes, discrete clusters of apatite mineral were present within the lumen, and in close proximity to the inner lipid membranes. These nascent crystallites eventually penetrated the lipid envelope to provide a focus for external precipitation events. Crystalline apatite phases were not observed when the incubation conditions prevented intraliposomal precipitation. The de novo calcification of these liposomes had many features in common with the sequence of mineral deposition occurring in matrix vesicle-mediated calcification. These results reinforce the conclusions of earlier chemical and kinetic studies and further support the use of this system as an experimental model for examining the membrane-mineral interactions associated with tissue mineralization.

Apatites↗

PubMed1991

Image analysis of collagen-associated mineral distribution in cryogenically prepared turkey leg tendons.

This study is concerned with the cryogenic preservation of intrafibrillar apatite distribution in type I collagen of turkey leg tendons. Cryogenic specimen preparations by the rapid freezing of nonfixed and noncryoprotected leg tendons were performed by two different protocols: (1) low temperature substitution, fixation and staining followed by low temperature embedment; (2) frozen hydrated and air-dried cryosections were examined with the electron microscope at -165 degrees C and normal operating temperatures, respectively. These protocols revealed the axial periodicity for mineralized collagen to have a 65-69 nm range with a mean value of 67 nm as determined by point-to-point measurements. Mineral distributions and specific apatite visualization were examined by electron microscopic imaging in bright field and selected-area dark field, respectively. Fourier filtered images and image subtraction were used to separate the axial repeating and nonrepeating intrafibrillar mineral domains of collagen. The removal of these axial repeats revealed an underlying and integrated mineral distribution, demonstrating that apatite is not confined to axial periodicities such as those of the gap zone.

Animals↗

PubMed2000

Ultrastructural properties of bone mineral of control and tiludronate-treated osteoporotic rat.

Bisphosphonates have been widely used in the treatment of human bone pathologies including osteoporosis. In this case, bisphosphonates have been shown to reduce bone resorption, thereby increasing the mass and mechanical resistance of bone. Determining the effects of these molecules on the properties of the bone apatite crystals could provide a better insight into the mechanism of bisphosphonate/bone interaction. The aim of this study was to determine the ultrastructural effects of a third generation bisphosphonate (tiludronate) on the morphology, size, distribution, chemical composition, and structure of apatite crystals in bone (trabecular) in a rat osteoporotic model. Four groups of rats were studied: (1) sham operated, (2) untreated ovariectomized (OVX), (3) OVX rats which received 35 mg/kg of tiludronate, (4) OVX rats which received 160 mg/kg of tiludronate. The rats of groups 3 and 4 received tiludronate orally in 2 consecutive days every week for 1 year. Scanning electron microscopy (SEM), high and low resolution transmission electron microscopy (TEM), and electron microprobe analysis (EDX) were used for the ultrastructural characterization of the bone mineral. This study demonstrated that tiludronate slightly increased the width of bone apatite crystals without changing any other crystal characteristics.

Animals↗

PubMed2004

Morphological and immunological characteristics of nanobacteria from human renal stones of a north Indian population.

The aim of this study was to detect, isolate and characterize the nanobacteria from human renal stones from a north Indian population, and to determine their role in biomineralization. Renal stones retrieved from the kidneys of 65 patients were processed and subjected to mammalian cell culture conditions. The isolated bacteria were examined using scanning (SEM) and transmission electron microscopy (TEM). They were characterized for the presence of DNA, proteins and antigenicity. The role of these bacteria in biomineralization was studied by using the (14)C-oxalate based calcium oxalate monohydrate (COM) crystallization assay. We observed the presence of apatite forming, ultrafilterable gram negative, coccoid microorganisms in 62% of the renal stones. SEM studies revealed 60-200 nm sized organisms with a distinct cell wall and a capsule. TEM images showed needle like apatite structures both within and surrounding them. They were heat sensitive, showed antibiotic resistance and accelerated COM crystallization. A potent signal corresponding to the presence of DNA was observed in demineralized nanobacterial cells by flow cytometry. The protein profile showed the presence of several peptide bands of which those of 18 kDa and 39kDa were prominent. Apatite forming nanosized bacteria are present in human renal stones and may play a role in the pathophysiology of renal stone formation by facilitating crystallization and biomineralization. However, further studies are required to establish the exact mechanism by which nanobacteria are involved in the causation of renal stones.

Antibodies, Bacterial↗

PubMed2001

Formation and transformation of calcium phosphates: relevance to vascular calcification.

Only one phase, carbonate apatite, is present in the mineral phase of normal calcification while different calcium phosphate phases are found in the mineral phases of pathological calcifications. In vascular calcification, the mineral phase has been described as hydroxyapatite; carbonate apatite, amorphous calcium phosphate. It has also been speculated that octacalcium phosphate may be a precursor for the apatite. This paper provides a brief review of: (1) the different calcium phosphates in normal and pathological calcifications; (2) the conditions for the formation and transformation of biologically relevant calcium phosphates in synthetic systems and a concise discussion on the relevance of results from synthetic systems to the calcium phosphate phase(s) involved in vascular calcification.

Apatites↗

PubMed2005

Biomimetic mineralization of partially bioresorbable glass fiber reinforced composite.

The aim of this study was to investigate the biomimetic mineralization on the surface of a glass fiber reinforced composite with partially resorbable biopolymer matrix. The E-glass fibers were preimpregnated with a novel biopolymer of poly(hydroxyproline) amide, and further impregnated in the monomer system of bis-phenyl glycidyl dimethacrylate (Bis-GMA)--triethylene glycol dimethacrylate (TEGDMA), which formed interpenetrating polymer networks (IPN) with the preimpregnation polymer. After light-initiated polymerization of the monomer system, the rhombic test specimens (n = 6) were immersed in the simulated body fluid (SBF) with the bioactive glass for 24 h, and then the apatite nuclei were allowed to grow for 1, 3, 5 and 7 days in the SBF. The control test specimens (n = 3) were immersed in SBF without the bioactive glass. According to the scanning electron microscope (SEM), a mineral layer was formed on the surface of all the specimens, which were immersed with bioactive glass. The layer was thickened by the prolonged immersion time to a uniform layer. The Ca/P atomic ratio of the mineral varied between 1.30 and 1.54 as analyzed by the energy dispersive X-ray analysis (EDXA). The Fourier transform infrared spectroscopy (FT-IR) spectra gave signals for the mineral, which are characteristic of both bone-like apatite and orthocalciumphosphate. In conclusion, the mineral layer was formed on the surfaces of the specimens by biomimetic mineralization, the mineral being a mixture of bone-like apatite, orthocalciumphosphate and other calcium phosphates.

Apatites↗

PubMed2006

Bond-coating in plasma-sprayed calcium-phosphate coatings.

The influence of bond-coating on the mechanical properties of plasma-spray coatings of hydroxyatite on Ti was investigated. Plasma-spray powder was produced from human teeth enamel and dentine. Before processing the main apatite coating, a very thin layer of Al2O3/TiO2 was applied on super clean and roughened, by Al2O3 blasting, Ti surface as bond-coating. The experimental results showed that bond-coating caused significant increase of the mechanical properties of the coating layer: In the case of the enamel powder from 6.66 MPa of the simple coating to 9.71 MPa for the bond-coating and in the case of the dentine powder from 6.27 MPa to 7.84 MPa, respectively. Both tooth derived powders feature high thermal stability likely due to their relatively high content of fluorine. Therefore, F-rich apatites, such those investigated in this study, emerge themselves as superior candidate materials for calcium phosphate coatings of producing medical devices. The methods of apatite powder production and shaping optimization of powder particles are both key factors of a successful coating. The methods used in this study can be adopted as handy, inexpensive and reliable ways to produce high quality of powders for plasma spray purposes.

Apatites↗

PubMed2002

Pathogenesis of cartilage calcification: mechanisms of crystal deposition in cartilage.

Apatite crystals form in physiologically calcified tissues, including the hyaline cartilage of the epiphyseal growth plate. While apatite crystals appear as unwanted deposits in other cartilage sites, more frequently, crystalline materials other than or in addition to apatite develop in dystrophic cartilage deposits. These crystalline materials include calcium pyrophosphate dihydrate and other calcium phosphate and calcium carbonate phases, monosodium urate, calcium oxalate, cholesterol, and crystallized proteins. This review describes the physical chemistry of crystal deposition and the events that occur in the growth plate as a basis for understanding the pathogenesis of nonphysiologic crystal deposition in cartilage.

Apatites↗

PubMed1982

Fluoride deposition in the bones of rats determined by fluoride and X-ray diffraction analysis.

Rats were given drinking water containing up to 300 parts/10(6) F and the conversion of hydroxyapatite to fluoridated apatite was estimated chemically and by X-ray diffraction. The differences of the mean fluoride uptakes from the very different concentrations of fluoride given were significant. Prolonged washing of the bones with demineralized water released 5-10 per cent from the fluoride uptake. Formation of fluoridated apatite was evident by decreases in the a parameter of the hydroxyapatite phase. In the washed bones, there was no appreciable transformations in the a parameters. The co-existence of Mg-containing beta-Ca3(PO4)2 with the apatite phase was detected in heated bone samples. The amount of beta-Ca3(PO4)2, its dependence on the age of the bones and its Mg content are interdependent.

Animals↗

PubMed1985

An X-ray diffraction and solubility study of equilibration of human enamel-powder suspensions in fluoride-containing buffer.

Various amounts of enamel-apatite powder were suspended in an acetate buffer (pH 4.5) containing sufficient fluoride to give molar ratios of fluoride/apatite from zero to unity. The suspensions were equilibrated at 20 degrees C for periods between 4h and 1 year, with continuous gentle stirring. Solubility studies showed dissolution of hydroxyapatite, formation and re-dissolution of calcium fluoride and formation of fluorapatite. The amount of mineral dissolved was low during the fluorapatite formation and increased by a factor of approx. 10 as equilibrium was approached. The fluoride content of the solid apatite, which ranged from 0.1 to 70 mol% fluorapatite, only influenced the solubility slightly, whereas the fluoride content of the bathing solution had a large effect. X-ray diffraction showed a linear correlation between the fluoride content and the a-axis of the apatite.

Apatites↗

PubMed2005

Production of ultra-fine bioresorbable carbonated hydroxyapatite.

Ionic-substituted hydroxyapatite (HAp) based materials may be a better choice than pure HAp owing to their similarity in chemical composition with biological apatite. The present study reports a process for the production of carbonated hydroxyapatite (CHAp) using microwaves. The CHAp was evaluated for its phase purity, chemical homogeneity, functionality, morphology, and solubility. The CHAp thus obtained was compared with a pure HAp and a biological apatite, which provides quite an interesting insight into the carbonate substitution. The in vitro ionic dissolution rates determined under physiological conditions clearly demonstrate the soluble nature of CHAp compared to HAp. The overall results indicate that the processed CHAp has increased resorption relative to pure HAp and has a chemical composition corresponding to some extent with that of biological apatite.

Apatites↗

PubMed2005

Distribution and partitioning of phosphorus in solid waste and sediments from drainage canals in the industrial belt of Delhi, India.

Phosphorus is an essential and often limiting nutrient in both marine and freshwater ecosystems. However, its oversupply is of great concern in many environments due to its role in eutrophication. The concentration and distribution of sediment bound phosphorus species not only record its input into the environment, but also suggest their possible sources. It is recognized that the features of phosphorus behaviour have not been extensively studied in urban environments. In this study, phosphorus in solid waste and sediments from drainage canals within the industrial belt of Delhi were fractionated into five operationally defined forms, i.e., exchangeable or loosely sorbed phosphorus (Exch-P), Fe-bound phosphorus (Fe-P), authigenic apatite, CaCO3-bound phosphorus and biogenic apatite (Acet-P), detrital apatite (Det-P) and organic-bound phosphorus (Org-P), in order to assess the potential bioavailability status in these systems.

Apatites↗

PubMed2003

Bonding mechanism and ultrastructural interfacial analysis of a single-step adhesive to dentin.

OBJECTIVES: to characterize the interaction of 4-acryloxyethyltrimellitic acid (4-AET), a key ingredient in a commercial all-in-one adhesive (Reactmer Bond) with dentin apatite, to measure the solubility of 4-AET calcium (4-AETCa), and to examine the ultrastructure of the resin-dentin interface bonded by this adhesive. METHODS: solubility of synthesized 4-AETCa in several solutions was measured. Flattened bovine dentin blocks were treated with 0.1wt% NaOCl for 10 min, or 5.0wt% NaOCl for 10 min, or 30 min. Fourier transform infrared analysis using attenuated total reflection (FT-IR/ATR) was performed on these four substrates before and after treatment with a 4-AET mixture (4-AET/HEMA: 40/60wt%). Undemineralized, unstained sections of human sound dentin that were bonded with the same comonomers were examined by transmission electron microscopy (TEM). RESULTS: the respective solubilities of the 4-AETCa in water, 2-hydroxyethyl methacrylate (HEMA; 100wt%) and HEMA/water (70/30wt%) were 0.023, 0.003 and 0.014 mol/l after 2 min. The IR analysis indicated that Ca-carboxylate (new bands: nuCz.dbnd6;O:1580 and 1413 cm(-1)) was formed on all dentin specimens following application of 4-AET, with or without NaOCl pretreatment. TEM showed a 1 micro m thick hybrid layer with some remnant apatite crystallites that were encapsulated by a layer of less electron-dense material. SIGNIFICANCE: the results suggest that ionized carboxyl groups in 4-AET may interact with Ca(2+) from apatite crystallites within the partially demineralized hybrid layer to form an insoluble calcium salt (4-AETCa) that may aid in bonding this resin system to dentin.

Animals↗

PubMed2001

Role of acid attack in the in vitro bioactivity of a glass-ceramic of the 3CaO.P2O5-CaO.SiO2-CaO.MgO.2SiO2 system.

A non-bioactive glass-ceramic (GC13) that contains hydroxyapatite (Ca5(PO4)3OH), diopside (CaMg(SiO3)2) and althausite (Mg2 PO4OH) as crystalline phases has been obtained by thermal treatment of a parent bioactive glass (G13) of nominal composition (wt%) 40.0 CaO-34.5 SiO2-16.5 P2O5-8.5 MgO-0.5CaF2. To induce bioactivity, GC13 was chemically treated with 1 M HCl for different periods of time. After chemical etching the in vitro studies showed formation of an apatite-like surface layer. In this article the influence of etching time both on the surface composition of the glass-ceramic and on the growth rate of the apatite layer is studied. It is concluded that the presence of hydroxyapatite in the glass-ceramic, associated to microstructural fluctuations, can favour apatite deposition in vitro.

Apatites↗

PubMed2002

Hydrothermal modification of titanium surface in calcium solutions.

Hydrothermal modification of a titanium surface in calcium solutions was performed. The apatite precipitation on the modified surface in Hanks' solution, as a simulated body fluid, was evaluated and the surface microstructure changes after the modification were characterized by thin-film X-ray diffractometry (TF-XRD) and X-ray photoelectron spectroscopy (XPS). Hydrothermal modification in CaO solution enhanced the precipitation of apatite on the titanium surface. High pH, high pressure and high temperature of the CaO solution increased the thickness of the surface-modified layer and enhanced the synthesis of calcium titanate which possibly promoted the precipitation of apatite in Hanks' solution. Hydrothermal modification in CaCl2 solution, on the other hand, showed reverse effects. The modification of titanium in CaO solution with hydrothermal treatment is expected to result in excellent osteointegration and can be easily performed by using an autoclave, a clinical apparatus widely used.

Apatites↗

PubMed2003

The chitosan prepared from crab tendons: II. The chitosan/apatite composites and their application to nerve regeneration.

The chitosan tubes derived from crab tendons form a hollow tube structure, which is useful for nerve regeneration. However, in order to use the chitosan tubes effectively for nerve regeneration, there remain two problems to be solved. First, the mechanical strength of the tubes is quite high along the longitudinal axis, but is somewhat low for a pressure from side. Second, the chitosan tube walls swell to reduce the inner space of the tubes in vivo. These two problems limit the clinical use of the chitosan tubes. In this study, to solve the problems, apatite was made to react with the chitosan tubes to enhance the mechanical strength of the tube walls. Transmission electron microscopy showed that apatite crystals were formed in the walls of the chitosan tubes. The c-axis of the crystals aligned well in parallel with chitosan molecules. These results indicate that the apatite crystals grow in the tubes starting from the nucleation sites of the chitosan molecules, probably by forming complexes with amino groups of chitosan and calcium ions. Further, the tubes were thermally annealed at 120 degrees C to prevent from swelling, and simultaneously formed into a triangular shape to enhance the stabilization of the tube structure. By these treatments, the hollow tubes could keep their shape even in vivo after implantation. Animal tests using SD rats further showed that the chitosan tubes effectively induced the regeneration of nerve tissue, and were gradually degraded and absorbed in vivo.

Animals↗