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Biomedical subjects

G Bonel

Publications and source records attributed to G Bonel.

13 recordsLinked to original sources
PubMed1992

Colour centres in plasma-sprayed hydroxyapatite.

Very pure hydroxyapatite is diamagnetic and shows no electron paramagnetic resonance (EPR) spectrum. Plasma-sprayed coatings made with such a pure hydroxyapatite contain paramagnetic point-defects. Irradiated deposits show a strong EPR absorption assigned to an O2- anion adjacent to a calcium vacancy, with anisotropic parameters, g1 = 2.004, g2 = 2.013 and g3 = 2.038. The EPR spectra and colour fade away following thermal annealing. These features are discussed in terms of point-defects in the hydroxyapatite crystal structure.

Color↗
PubMed1989

Ex-vivo study of molecular interfaces in calcified tissues.

The aim of this work is the characterization of interfaces in calcified tissues. Thermally Stimulated Currents and Gel Permeation Chromatography have been used for investigating extracts and residues from calf femoral diaphysis, at various stages of demineralization. In residues, the evolution of molecular mobility shows that the organic-mineral linkage is insured by several proteins: Collagen is not directly linked to apatite.

Animals↗
PubMed1988

Physicochemical characterization of deposits associated with HA ceramics implanted in nonosseous sites.

Pellets of well-characterized microporous hydroxyapatite (HA) ceramic were implanted in hamsters in two nonosseous sites: (1) in the fatty tissue of the gingival crease, far from bony tissue and (2) in intraperitoneal sites. The implants in site 1 were placed directly in contact with tissues, cells, and extracellular fluids while the implants in site 2 were placed in special chambers made of plexiglass cylinders covered in both ends with millipore filters, preventing contact with tissues and cells, but not with extracellular fluids. The hamsters were sacrificed and the implants recovered after 8, 16, 30, 150, and 365 days. The pellets were characterized using x-ray diffraction, infrared absorption, thermogravimetry, scanning and transmission electron microscopy, and calcium and phosphate analyses before and after implantation. Physicochemical analyses of HA ceramic implants before and after implantation demonstrated the formation of new material which was significantly different from the HA ceramic in terms of the following: (a) morphology (size of shape) of crystals; (b) intimate association of the inorganic phase of the new material with an organic phase similar to inorganic/organic association in bone; (c) the inorganic phase of the new material is a CO3-apatite, similar to that of bone, while the HA in ceramic is CO3-free; (d) electron diffraction of apatite of new material is similar to that of bone apatite. This study also demonstrated that the new material associated with the HA ceramics implanted in two different nonosseous sites were identical in spite of the differences in their microenvironment (cellular and acellular).

Animals↗
PubMed1988

Influence of preparation conditions on the composition of type B carbonated hydroxyapatite and on the localization of the carbonate ions.

It is shown how certain aspects of the composition and structure of carbonated apatites depend strictly on preparation conditions, for example, excess of phosphate or calcium ions in the reaction medium, CO32- concentration, pH, ammonia added or not. Depending on those conditions, either one or the other of the two proposed mechanisms of introduction of carbonate ions into the B sites is dominant. The mechanisms are (1) replacement of a phosphate ion by a carbonate ion with the formation of three vacancies, one in a phosphate oxygen site and one each in the neighboring Ca2+ and OH- sites; and (2) replacement of a phosphate ion by a carbonate accompanied by a hydroxyl ion. Whether mechanism (1) is observed to dominate over mechanism (2), or vice versa, is accounted for by the relative concentrations of the various ions in the reaction medium. The number of vacancies is decreased by the presence of either, or both, excess calcium ions or ammonia in the reaction medium. A structural-chemical mechanism is advanced for the view that, with the smallest CO32- content, the A sites are favored but with increasing carbonate content the B sites become favored and the A-site content becomes less than it is when the total carbonate content is less.

Carbonates↗
PubMed1988

Apatitic calcium orthophosphates and related compounds for biomaterials preparation.

The authors show that to obtain well chemically defined apatitic bioceramics and to know the possible transformations of this material during sintering, it is necessary to prepare a good starting material. Moreover, they show that it is possible to prepare a new organic-inorganic phosphate compound. The precipitation of apatite in an aqueous medium at boiling temperature was studied using the methodology of experimental design. Independent variables were the volume of NH4OH in phosphate solution, the volume of NH4OH in calcium solution, and the time of precipitation; the response was the atomic Ca/P ratio of the obtained precipitate. A continuous variation of this ratio from 1.63 to 1.73 is observed. Implications of this result to the preparation of pure HA: Ca10(PO4)6(OH)2 is given. Moreover, when Ca/P greater than 1.67, HA reacts with Ca(OH)2 (after heating at 1000 degrees C in air for some days) to give rise to a single phase described as a modified HA (MHA), a Ca/P ratio of 1.75, an a value of 9.373 +/- 0.002 A, and a c value of 6.884 +/- 0.002 A. The reactivity (time versus temperature) of the MHA is described. If the precipitation of the calcium phosphate is realized at 37 degrees C in a water-ethanol medium in the presence of A2EP, a new apatite, chemically bonded to the organic molecule by pooling phosphate groups, is obtained.

Ammonium Hydroxide↗
PubMed1987

Occurrence of nitrogenous species in precipitated B-type carbonated hydroxyapatites.

B-type carbonated hydroxyapatites, prepared in aqueous media free of alkali ions, fix ammonium ions present in the reaction medium. A small portion of the carbonate ions introduced into the apatite structure enter by the substitution mechanism (CO3(2-), NH4+)----(PO4(3-), Ca2+). With these results for the structural incorporation of ammonium ions, differences in lattice parameters observed among specimens with the same degree of carbonation were attributed to some substitution of NH4+ for Ca2+. The fixed ammonium ions were shown to be the source of the cyanamide and cyanate ions that develop on heating. Above 500 degrees C these apatites lost both the carbonate and the cyanate and cyanamide ions.

Carbonates↗
PubMed1987

Age-related changes in mineral of rat and bovine cortical bone.

The mineral of cortical bones has been studied in newborn, growing, and adult rats and in the calf and cow, using X-ray diffraction and infrared spectroscopy during the thermal decomposition of bones and by microassay of carbonate. The mineral of all the bone samples, regardless of species or age, was found to be a calcium-deficient apatite containing both CO3(2-) and HPCO4(2-) ions in the crystal lattice. The crystal size, Ca/P molar ratio, and CO3(2-) ion content of cortical bone all increased with increasing age in both the rat and the bovine. The Ca/P ratio varied from 1.51 in newborn rats to 1.69 in adults but remained that of Ca-deficient apatite even though its value was close to that of stoichiometric hydroxyapatite (1.67). Both the carbonate ion and the hydrogenophosphate ion contents varied from one animal species to another and with age within a given species. Maturation was correlated with an increase in carbonate ion content, which replaced the HPO4(2-) ions. In contrast, the calcium ion number per unit formula did not vary during maturation. Cortical bone mineral, in both species, regardless of age, can therefore be represented by the following formula: Ca8.3 (PO4)4.3 (CO3)x(HPO4)y(OH)0.3; y decreased and x increased with increasing age, (x + y) being constant, equal to 1.7.

Age Determination by Skeleton↗
PubMed1986

Crystallographic identification of a calcium deposit in calcified pericarditis associated with articular chondrocalcinosis.

In a case of CPPD crystal deposition disease of the pseudorheumatoid type and of long duration, calcified constrictive pericarditis developed and was surgically treated. Analysis of the calcium deposit in the pericardium was carefully made by infrared absorption, x-ray diffraction, and thermogravimetry. It revealed that the deposit was composed of B-type carbonated apatite. Previously, both calcium pyrophosphate dihydrate (CPPD) and apatite crystals, either in the same place or in different tissues, have been reported in the same patient. These observations raise the possibility that the same metabolic error might lead to both types of crystal deposition.

Apatites↗
PubMed1986

[Microanalysis of salivary calculi].

Eight salivary calculi were sectioned along a plane of symmetry and the sections studied by microanalysis. Three different regions were observed: a central region with one or several strongly mineralized nuclei, a stratified, less mineralized region with a lower Ca/P ratio and finally a peripheral weakly calcified region. Although inclusions with high silicium or sulfur concentrations were found in all samples, their role in the genesis of calculus is not clear. Most often filamentous mineralized bacteria were observed by scanning electron microscopy on the external stone surface.

Microscopy, Electron, Scanning↗
PubMed1978

Types of "H2O" in human enamel and in precipitated apatites.

Types of "H2O" in human enamel and in precipitated apatites are characterized using X-ray diffraction, infrared (IR) absorption spectroscopic and thermogravimetric analyses. Changes in lattice parameters (principally in the a-axis dimensions) and in the character of the IR absorption bands are correlated with weight losses at pyrolysis temperatures of 100 degrees to 400 degrees C and with effect of rehydration and reignition of previously ignited samples. This study demonstrated that the loss of "H2O" below 200 degrees C is reversible and causes no significant change in the lattice parameter of these apatites, whereas loss of "H2O" between 200 degrees and 400 degrees C is irreversible and causes a contraction in the a-axis dimension. It is proposed that two general types of "H2O" are present in these apatites: (a) adsorbed H2O--characterized by reversibility, thermal instability below 200 degrees C, and lack of effect on lattice parameters; and (b) lattice H2O--characterized by irreversibility, thermal instability between 200 and 400 degrees C, and induction of expansion in the a-axis dimensions of human enamel and precipitated apatites. Lattice H2O is assumed to be due to H2O-for-OH and/or HPO4-for-PO4 substitutions in these apatites. Loss of adsorbed H2O caused sharpening of the OH absorption bands in the spectra of these apatites. Loss of lattice H2O caused the appearance of P-O-P absorption bands (due to the presence of P2O74- group) in precipitated apatites containing small amounts of CO32-.

Adult↗