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Biomedical subjects

G Bonel

Publications and source records attributed to G Bonel.

At least 19 recordsLinked to original sources
PubMed1997

The influence of sintering temperature on the proliferation of fibroblastic cells in contact with HA-bioceramics.

HA-ceramics used in human surgery as osteoconductive surfaces show a great variety of characteristics. Certain characteristics such as grain size, porosity, and surface area, are controlled by the sintering temperature of the slurry. We grew L-929 fibroblast cells on HA-ceramic disks that had been sintered at different temperatures ranging from 850 degrees-1350 degrees C. The cell line growth rate was lower on ceramic disks than on the culture-grade polystyrene used as a negative control. Cell growth correlated with the ceramic sintering temperature although no significant difference in the cell adhesion to the different ceramics was shown. Growth rate on ceramics sintered at low temperatures (850 degrees and 950 degrees C) was negative whereas it was positive on disks sintered at higher temperatures. When the cells were separated from the disks by a polycarbonate membrane, the growth rate was negative on those membranes in contact with low-temperature sintered disks and positive on the high-temperature sintered disks. The calcium and phosphorus concentration in the culture medium in contact with ceramics sintered below 1050 degrees C decreased during the culture period. Ceramics sintered between 1100 degrees and 1250 degrees C brought about an increase in Ca and P concentrations while ceramics sintered at higher temperatures did not induce any changes. SEM examination of the 850 degrees and 1200 degrees C sintered ceramics showed that the 850 degrees C sintered ceramics consisted of small grains with pores between them and the 1200 degrees C sintered ceramics were made of larger grains without any visible pores, thereby decreasing the surface of material in contact with the culture medium. This difference in surface area was confirmed by the fact that the amount of albumin absorbed onto the ceramic was dependent on the sintering temperature. In conclusion, the modification of the culture medium brought about by high-surfaced ceramics could influence the growth of cells with which such ceramics come in contact.

Animals↗
PubMed1994

Two-year outcome of hydroxyapatite-coated prostheses. Two femoral prostheses retrieved at autopsy.

We performed a histological study of the bone-implant interface on 2 human femurs implanted with a hydroxyapatite-coated self-locking stem for 2 years. Extensive bone formation with no intervening fibrous tissue was noted around the entire circumference of the 2 prostheses. The newly-formed bone had 2 morphotypes: an alveolar disposition with a continuous contact between bone and hydroxyapatite, and a digitiform one where distinct bony trabeculae were in contact with the ceramic coating or with the bone marrow. Partial or even total resorption of the hydroxyapatite coating was clearly identified, these areas showing bone in contact with the metal.

Aged↗
PubMed1993

[Histological analysis of the bone/prosthesis interface in man after implantation of a hip prosthesis coated with plasma-sprayed hydroxyapatite].

Thin coatings of calcium phosphate hydroxyapatite on metal alloys provide to these materials biological properties of calcium phosphates. We have analysed, using histological techniques or newly developed scanning electronic microscopy techniques, hip prostheses implanted into humans for periods from a few days up to twenty six months. The results of these analyses confirm the good osteointegration of these prostheses observed during clinical studies. Moreover, an active remodeling of the bone in contact with the ceramic-coating was observed. The coating was also concerned by the remodeling process and evolved once implanted.

Bone Matrix↗
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↗
PubMed1986

[Physicochemical analysis of subcutaneous calcifications in a case of Thibierge-Weissenbach syndrome].

A physicochemical study of subcutaneous calcium deposits was performed in a patient with typical Thibierge-Weissenbach syndrome which had begun, ten years previously, with Raynaud's phenomenon and sclerodactylia. Calcium deposits had progressively developed, forming large plates on the arms, flanks and thighs. In the course of the disease they had become ulcerated, exuding a white, chalky material. X-ray films and xerograms demonstrated the extent of these deposits. The calcium-phosphorus balance was normal, and the other clinical and laboratory examinations were concordant with a diagnosis of Thibierge-Weissenbach syndrome (calcinosis). Only systemic corticosteroid therapy slowed down the pathological process; calcium chelating agents (diphosphonate) proved ineffective. The physicochemical study showed that the deposits consisted of carbonated apatite type B with the following formula: Ca8.0(PO4)4.1(CO3)1.2(HPO4)0.8 The mineral substance seemed to be less reactive and more stable than normal bone. This would account for the total lack of effectiveness of all treatments, notably calcium chelating agents, on the course of the deposits. Treatments usually produce bone demineralization before they influence the calcium deposits. This study provides much more detailed information than was hitherto available on calcium deposits and on carbonate ion contents in the apatite phase. The presence of carbonates increases the solubility and reactivity of calcium apatite.

Calcinosis↗
PubMed1982

X-ray diffraction of calcined bone tissue: a reliable method for the determination of bone Ca/P molar ratio.

A method is proposed which allows direct measurement by X-ray diffraction of the Ca/P molar ratio in bone tissue after calcination at 900 degrees C. It is based on the construction of a standard curve from known mixtures of hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TP), since these are the only two crystallized mineral phases in the bone ash after its calcination at 900 degrees C. This method, based on physical analysis, may also be used to calculate the respective proportions of calcium and phosphorus after the Ca/P molar ratio has been obtained. It is more sensitive than and at least as accurate as the usual chemical techniques, even though it can be applied to minute samples of bone tissue. Furthermore, the method permits simultaneous determination of lattice parameters and provides additional information about bone mineral structure.

Animals↗
PubMed1982

[Thermal stability of carbonates in bone tissue].

The analysis shows that carbonate ions present in the mineral phases of calcified tissues are decomposed in two steps during their ignition. These carbonate ions might be all localised in the phosphate sites of the apatitic structure (B type carbonate apatite). The loss of one important part of carbonate ions at a abnormally low temperature (250 degrees C) might result from an intracristalline reaction between these ions and HPO4(2-) or P2O7(4-) ions present in the apatitic structure.

Animals↗
PubMed1981

ESR of CO2- in X-irradiated tooth enamel and A-type carbonated apatite.

Using both low microwave power and weak magnetic field modulation, we have shown that the asymmetric signal arising in X-irradiated tooth enamel as well as in A-type carbonated apatite exposed to X-rays or to excited oxygen has an orthorhombic character and must be attributed to CO2-. Effectively, the mean values found for the three g-tensor components are comparable to those quoted for this defect in single-crystal specimens of calcite and sodium formate.

Apatites↗