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At least 649 records · Page 36Linked to original sources

PubMed1982

Apatites in heterotopic calcifications.

Calcified material obtained from three patients suffering from calcifications of the shoulder tendon sheath and from a subcutaneous with calcinosis was studied. A panel of different techniques was applied to this study: scanning electron microscopy, X-ray diffraction, infrared spectrometry, scanning and transmission wavelength dispersive X-ray spectrometry, high resolution transmission electron microscopy and electron microdiffraction. These calcifications, made of carbonate containing apatite, are heterogeneous and composed of at least two separate phases the crystallinity of which appear different.

Apatites↗

PubMed1994

Crystallographic and chemical analysis of human bone apatite (Crista Iliaca).

Crystallographic (X-ray diffraction) and chemical (X-ray fluorescence and combustion analysis) investigations on bone microsamples (human iliac crest of 111 individuals aged 0-90 years) reveal that certain crystallographic and chemical parameters (lattice parameters, crystallinity, chemical compounds, biomineralic fraction...) are closely related to aging and type of tissue (corticalis and spongiosa). In juvenile bone [0-25y], the biomineralic fraction rises significantly, as does crystallinity and area of apatite (002)-reflection indicating a growth of crystal size. The second main age interval [25-50y] does not display statistically relevant variations with age. The third main age group [50-90y] is characterized by large chemical variations, probably due to overlapping effects of age and declining health.

Adolescent↗

PubMed1994

Assessment of the respiratory system in workers occupationally exposed to phosphorite and apatite dusts.

The respiratory system in 118 male workers occupationally exposed to phosphorite and apatite dusts was assessed. Subjective, physical and spirographic examinations were performed and chest X-ray pictures were taken. No significant differences between the exposed workers and the control group were found. There was only a statistically significant decrease in spirometric parameters in the exposed group in comparison with controls. There was no such relationship in regard to the length of employment and smoking habit. In the exposed group there were no significant disturbances of the lung ventilation efficiency.

Adult↗

PubMed1993

Assessment of the nasal mucosa in workers exposed to the prolonged effect of phosphorite and apatite dusts.

One hundred and thirty one workers occupationally exposed to phosphorite and apatite dusts and a control group underwent repeated laryngological and cytological examinations of nasal mucosa smears. The clinical examination showed chronic simple or atrophic rhinitis. The cytological test revealed metaplasia of the respiratory epithelium towards squamous epithelium in all smears. Both the rate of catarrhal changes and the degree of epithelial metaplasia varied with the duration of exposure.

Adult↗

PubMed1993

Spectrum decomposition through maximum likelihood common factor analysis of the EPR spectra of Na+ containing carbonated apatites dried at 400 degrees C.

X-irradiated carbonated apatites precipitated from aqueous solutions and dried at 400 degrees C until constant weight are investigated with electron paramagnetic resonance (EPR). The carbonate content of the samples studied ranges from 8.12 to 21.0 wt%. The observed multicomponent EPR spectra are analyzed with maximum likelihood common factor analysis (MLCFA), a multivariate statistical technique. Once the correct number of constituents are determined and the factor spectra estimated by MLCFA, a minimization procedure is performed in order to transform the abstract factor spectra linearly into an equal number of real EPR powder spectra. The spin hamiltonian parameters of the component spectra thus obtained are used to characterize and identify the different paramagnetic radicals. A comparison with values from the literature is made. A spectrum decomposition study of all the observed multicomponent EPR spectra in terms of the isolated constituents is successfully performed as a function of the carbonate content of the samples.

Analysis of Variance↗

PubMed1993

Acute apatite podagra with negative birefringent spherulites in the synovial fluid.

We describe a young male patient who presented with acute podagra after jogging activity. He had no underlying pathology. Polarized light microscopy of the synovial fluid from his first metatarsophalangeal joint revealed numerous negative birefringent spherulites about 6 microns in diameter, presenting the typical appearance of Maltese crosses. The molar calcium/phosphorus ratio of these spherulites as determined by X-ray energy dispersive analysis was virtually identical to that of synthetic or pathologic apatite.

Acute Disease↗

PubMed1997

Matrix vesicles in osteomalacic hypophosphatasia bone contain apatite-like mineral crystals.

Hypophosphatasia, a heritable disease characterized by deficient activity of the tissue nonspecific isoenzyme of alkaline phosphatase (TNSALP), results in rickets and osteomalacia. Although identification of TNSALP gene defects in hypophosphatasia establishes a role of ALP in skeletal mineralization, the precise function remains unclear. The initial site of mineralization (primary mineralization) normally occurs within the lumen of TNSALP-rich matrix vesicles (MVs) of growth cartilage, bone, and dentin. We investigated whether defective calcification in hypophosphatasia is due to a paucity and/or a functional failure of MVs secondary to TNSALP deficiency. Nondecalcified autopsy bone and growth plate cartilage from five patients with perinatal (lethal) hypophosphatasia were studied by nondecalcified light and electron microscopy to assess MV numbers, size, shape, and ultrastructure and whether hypophosphatasia MVs contain apatite-like mineral, as would be the case if these MVs retained their ability to concentrate calcium and phosphate internally despite a paucity of TNSALP in their investing membranes. We found that hypophosphatasia MVs are present in approximately normal numbers and distribution and that they are capable of initiating internal mineralization. There is retarded extravesicular crystal propagation. Thus, in hypophosphatasia the failure of bones to calcify appears to involve a block of the vectorial spread of mineral from initial nuclei within MVs, outwards, into the matrix. We conclude that hypophosphatasia MVs can concentrate calcium and phosphate internally despite a deficiency of TNSALP activity.

Apatites↗

PubMed1978

[A method for measuring apatite crystals in human dentine by high resolution transmission electron microscopy].

High resolution electron microscopy now makes it possible to use an original method for measuring biological apatite crystals. The crystals of intertubular sound dentine have an average width of 296 A (standard deviation: 37) and an average thickness of 32 A (standard deviation: 5). During the course of so-called arrested caries, crystals get twice as thick compared to those sound dentine, whereas their width remains unchanged.

Apatites↗

PubMed1997

-Apatite rheumatism, unusual aspects-.

Apatite calcifications may be responsible for unusual aspects. Clinically they may mimick sepsis or soft tissue tumor, and radiologically a bone tumor or soft tissue tumor-like lesion with respect to the erosion of the bone cortex adjacent to an unusual calcification. Diagnosis is based on knowledge of atypical sites of calcification, CT, and mainly, radiological regression of the calcification after a short follow-up.

Apatites↗

PubMed1997

[The crystallization feature of a castable apatite glass-ceramics].

The crystallization feature of a castable apatite glass-ceramics was studied by the means of DTA, XRD and SEM. The effect of chemical composition on the microsturcture of the glass-ceramics was discussed. The introduction of MgO and Al2O3 into the system has a substantial influence on the crystallization feature.

Apatites↗

PubMed1997

The bone-bonding polymer Polyactive 80/20 induces hydroxycarbonate apatite formation in vitro.

The bone-bonding polymer known as Polyactive is a block copolymer composed of a polyethylene oxide (PEO) soft segment and a polybutylene terephthalate (PBT) hard segment. This study focuses on the in vitro induction of hydroxyapatite by Polyactive. Our results show that Polyactive is capable of inducing hydroxycarbonate apatite (HCAp) formation from a metastable calcium phosphate solution analogous to a physiological solution. In a 4-day incubation, the HCAp formation extended approximately 100 microm deep from the surface. A great number of globules about 1 microm large were found in the calcified Polyactive. These globules were composed of HCAp crystals embedded in the polymer matrix. There were so many globules in the surface that they connected with each other and formed a calcified layer. Next to the calcified layer was a zone where the globules were scattered. The calcified surface may have acted to promote HCAp growth from the solution, bringing about the formation of a HCAp layer on top of the calcified layer. The transition of solid Polyactive into a Polyactive hydrogel in calcium phosphate solution permitted HCAp formation within the polymer. It is proposed that the COOH groups produced during hydrolysis of Polyactive play an important role in nucleating hydroxyapatite. A remarkable affinity of the PEO segment of the polymer for calcium ions may facilitate moving calcium and phosphate from the solution into the polymer for the growth of HCAp.

Biocompatible Materials↗

PubMed1990

Evidence that apatite crystals of rat incisor enamel have hexagonal cross sections.

Images of nearly cross sectioned enamel crystals obtained with the transmission electron microscope were examined in detail and correlated with various possible cross-sectional shapes of the crystals. The following images were seen: 1) elongated hexagons with sharp outlines, maximal density, and minimal size (type A profile); 2) elongated hexagons with one pair of long sides of high contrast, two pairs of short sides of low contrast, high density in the center of the image, and low density towards the low contrast sides (type B profile); 3) slanted hexagons with one pair of high contrast sides, two pairs of low contrast sides (one pair of long, one pair of short sides), and the density decreasing from the center towards the low contrast sides (type C profile); this profile was seen more frequently than the type B profile; and 4) octagons with low contrast edges all around, the density decreasing from the center towards the edges (type D profile). Types B, C, and D profiles were larger than type A profiles. Similar crystal images have been described in the literature. When tilting a specimen in increments of 6 degrees, the transformation of type A to type C and type C to type D profiles was observed. Many crystal images did not change their shape greatly when tilting the section through 6 degrees. No rectangular or rhomboidal profiles were seen. It is argued that types A, B, C, and D profiles cannot be generated by apatite crystals with a parallelepiped cross section. They are easily explained, however, on the basis of crystals with hexagonal cross section.

Animals↗

PubMed1993

Analysis of apatite deposits on substrates.

Calcium phosphate coatings, important for medical implant applications can occur in several different phases. Because of differences in properties of these phases it is imperative to be able to identify their presence in a substrate's coating. In this study we characterized hydroxy apatite (HA) surfaces applied by four different coating procedures. Included were plasma sprayed, sputtered, a composite, and a composite overlayed with plasma sprayed. It was found that a combination of reflectance infrared and Raman spectroscopy could be utilized to make an in situ characterization of the calcium phosphate phases. It was shown that plasma sprayed and sputtered coatings of HA lost OH and thus decreased in crystallinity, while composite coatings remained unchanged from the original HA powder.

Biocompatible Materials↗

PubMed1994

Dual constant composition kinetics characterization of apatitic surfaces.

The use of calcium phosphate phases as implant materials in forms such as ceramic hydroxyapatite (CHAP) and hydroxyapatite plasma-coated implants (HPCTI) as well as the synthetic phases is now quite well established. Although conventional physical chemical characterization methods such as X-ray diffraction may indicate the exclusive presence of hydroxyapatite (HAP), there is little doubt that other calcium-containing surface impurities play important roles in the initial reactions that take place when such materials are brought into contact with aqueous phases. These surface impurities usually dissolve rapidly with the release of excess calcium and hydroxide ions. Based on the constant composition (CC) method, the dual constant composition (DCC) approach has been developed for investigating the dissolution kinetics behavior of these apatitic materials in an attempt to characterize and modify the surfaces, and possibly to predict their behavior when placed in vivo. The results of this study confirm the presence of highly reactive heterogeneous calcium-containing phases on the surface of materials such as CHAP and HPCTI, as evidenced by the release of appreciable amounts of calcium and hydroxyl ions upon introduction of these surfaces in saline solutions. Furthermore, these calcium phosphate phases exhibited a unique dissolution behavior when compared with synthetically prepared phases such as HAP and beta-tricalcium phosphate (beta-TCP), as suggested by the observation that they dissolve in solutions supersaturated with respect to HAP.

Calcium↗

PubMed2005

Hydroxy apatite microspheres enhance gap junctional intercellular communication of human osteoblasts composed of connexin 43 and 45.

The aseptic loosening of artificial joints with associated periprosthetic bone resorption may be partly due to the suppression of osteoblast function to form new bone by wear debris from the joint. To assess the effect of wear debris on osteoblasts, effects of model wear debris on gap junctional intercellular communication (GJIC) of normal human osteoblasts were estimated. The GJIC activity of the osteoblasts after a 1-day incubation with the microspheres was similar to that of normal osteoblasts. However, hydroxy apatite particles, which have been reported to enhance the differentiation of osteoblasts in contact with them, enhanced the GJIC function of the osteoblasts. From RT-PCR studies, not only connexin 43 but also connexin 45 is suggested to play a role in the GJIC of the osteoblasts in an early stage of coculture with the microspheres, although it is still unclear how these connexins work and are regulated in the GJIC and differentiation. However, this study suggests that there is a relationship between the early levels of GJIC and the differentiation of the cells. Therefore, estimating the effect of biomaterials, even in the microsphere form, on the GJIC of model cells, with which the biomaterials may be in contact in vivo, can provide important information about their biocompatibility.

Base Sequence↗

PubMed2005

Composition-controlled nanocomposites of apatite and collagen incorporating silicon as an osseopromotive agent.

The development of a novel biocomposite of apatite (Ap) and collagen incorporating low-level additions of silicon (Si) as an osseopromotive agent is detailed. Designed to mimic the structural and compositional characteristics of developing bone, this composite is produced via a coprecipitation method, through which the weight percentage of Ap (i.e., the Ap/collagen ratio) can be varied. Coprecipitates produced at Ap contents of 80 wt % (Ap/collagen=4:1), 60 wt % (Ap/collagen=3:2), and 40 wt % (Ap/collagen=2:3) Ap showed markedly different morphologies, ranging from ceramic-like particulates to rope-like macro-fibrils; at all three Ap contents, however, the nanostructural features of the composites remained qualitatively indistinguishable, with equiaxed Ap nanocrystals distributed randomly throughout a matrix of amorphous collagen. Si incorporation was observed to occur preferentially in the collagenous phase-a result with potential impact on local controlled release of Si.

Animals↗

PubMed2006

Biodegradation and bioabsorption innovation of the functionally graded bovine bone-originated apatite with blood permeability.

Bioabsorbable and functionally graded apatite (fg-HAp) ceramics were designed using bovine bone by the calcination and partial dissolution-precipitation methods. The fg-HAp ceramics that were developed had gradual distributions of the degree of crystallinity and the grain size of single-phase hydroxyapatite from the surface layer of the pore wall to the bulk structure region. Calcination at 1073 K gave a specific surface area of 30 m2 x g-1 and porosities of 60-80%. The pore structure of the fg-HAp was classified into two regions: a macro-pore region (100-600 microm) originating from spongy bone and a micro-pore region (10-160 nm) related to body fluid permeation and blood permeability. By implantation in subcutaneous tissue of rat, it was confirmed that body fluid permeated the bulk region of the fg-HAp ceramics through the micro-pores. The volumetric populations occupied by body fluid were 60% at 4 weeks and 68% at 8 weeks in the ceramics explants, indicating drastic bioabsorption, although the body fluid was found to be immunopositive for an albumin as the main serum protein in blood. On the fg-HAp ceramics developed here, the bioabsorption rate could be controlled by careful selection of the calcination temperature. These ceramics can be applied as new biomimetic ceramics exhibiting surface and bulk degradations and cellular absorption by giant cells.

Adsorption↗

PubMed2005

Cortical bone screw fixation in ionically modified apatite cements.

Hydroxyapatite cements are used in reconstruction of the face; usually in well-defined cavities where the cement can be stabilized without the need for internal fixation. A hydroxyapatite cement that could enable screw fixation and some loading therefore has considerable potential in maxillofacial reconstruction. It has been demonstrated recently that water demand of calcium phosphate cements can be reduced by ionically modifying the liquid component. This study investigated the capacity of an ionically modified precompacted apatite cement to retain self-tapping cortical bone screws. Screw pullout forces were determined in the direction of the screw long axis and perpendicular to it, using cortical bone and polymethylmethacrylate cement as a control. In bending pullout tests, measured forces to remove screws from ionically modified precompacted cement were insignificantly different from cortical bone. However, pullout forces of bone screws from hydroxyapatite cement decreased with aging time in vitro.

Bone Cements↗