Colloidal and monocrystalline Ln3+ doped apatite calcium phosphate as biocompatible fluorescent probes.

Ultrafine individualised mono crystalline Ca(10-x)(PO4)(6-x)(HPO4)x(OH)(2-x) deficient calcium hydroxyapatite nanocrystals displaying fluorescence under visible excitation are proposed for utilisation as biocompatible biological probes.

Europium-doped bioapatite: a new photostable biological probe, internalizable by human cells.

The authors prepared at low temperatures (37 degrees C) a novel inorganic bioprobe. It consisted of mineral nanoparticles of apatitic tricalcium phosphate doped with europium, of size, structure and composition close to those of the mineral part of calcified tissues. In contrast to organic probes which degrade rapidly (photobleaching), the red luminescence of the new probe is photostable. Moreover, this luminescence can be obtained under visible irradiation, which makes it suitable for prolonged examination of live cells. Human pancreatic epithelial cells in culture were incubated with these particles and their internalization was observed by laser scanning confocal microscopy. Transmission electron microscopy and electron microdiffraction analysis confirmed that the particles were internalized retaining their original apatitic structure. This probe may thus be of value for biovectorization.

Study of implantable calcium phosphate systems for the slow release of methotrexate.

The authors prepared and studied systems implantable in bone, for the slow release of an antineoplasic agent, methotrexate (MTX). The systems were made by compaction of a powdered mixture of an apatitic deficient calcium phosphate, dextran and various amounts of MTX. Used as a matrix, this calcium phosphate has outstanding adsorption and compaction properties. It is an osteoconductor and biodegradable. The in vitro study carried out on these systems showed that the release of MTX with time is slow and prolonged due to the phenomena of adsorption/desorption of MTX onto deficient apatite. The composition of the implants changed with time towards that of stoichiometric apatite. The in vivo pilot study was performed by implantation in the external femoral condyle of rabbits. A pharmacokinetic study revealed that the circulating concentration of MTX in the blood was always below toxic levels. Twenty percent of the initial MTX remained in the implants after 7 days. A study of the biocompatibility and bioreactivity showed no local necrosis at any time, while implants degraded and new bone formed simultaneously. These implantable systems seem appear suitable for use immediately.

Stability study of tetracyclines with respect to their use in slow release systems.

In the aim of optimizing implantable slow-release systems for the local delivery of antibiotics, the stability of tetracyclines was studied in water at 37 degrees C or under gamma irradiation. Four tetracyclines in their chlorhydrate form were chosen depending on their hydrophilic/hydrophobic balance. Their chemical stability was established by HPLC, and biological stability by bacteriological tests. It was shown that methacycline and doxycycline are stable in water for three days. Tetracycline and minocycline exhibit limited decomposition (less than 10%) under the same conditions. So, in vitro drug release for at most three days, appears to be possible. Besides, all four tetracyclines either in powdered form or included in a calcium phosphate matrix, kept their bacteriological activity after gamma irradiation at 32.4 kGr. Consequently, the in vivo study of these implantable slow drug release systems, can be carried out.

X-ray photoelectron spectroscopy study of the dentin-glass ionomer cement interface.

OBJECTIVES: The work was carried out with a view to identifying the elements composing the glass ionomer under study, and then to characterising the interactions occurring between this particular glass ionomer and the dentin substrate on which it was placed and with which it interacted. METHODS: The samples studied were sections of healthy human dentin on which a very thin film of auto-polymerisable cement, composed of a powder and a liquid, was deposited under para-clinical conditions. After separation, the interfaces on the dentin side and on the glass ionomer side were studied using X-ray Photoelectron Spectroscopy (XPS). RESULTS: This study showed that the dentin and glass ionomer cement exchanged mineral and organic elements. The acid contained in the liquid showed a certain degree of aggressivity, despite the presence of the glass ionomer. The dentin protein was, in fact, rapidly denuded from the very first minute. Migration of the mineral elements from one substrate to the other led to the formation of an intermediate layer on the surface of the materials. SIGNIFICANCE: This layer, which forms an interphase, enables the material to adhere to the dentin.

Structural characteristics of a globular protein investigated by X-ray photoelectron spectroscopy: comparison between a legumin film and a powdered legumin.

Films of legumin, a pea protein, were deposited onto a glass support using the Langmuir-Blodgett method, at various surface pressures. XPS study of these films show that their thickness increases with the deposition pressure. At the pressure limits of films stability, the thickness values (respectively 73 and 110 A) are close to the protein dimensions. Layered at low pressure, the oblate protein stands up when pressure increases. Furthermore, XPS study shows that the orientation of the external flexible loops depends on the obtention conditions. Thus, in the case of Langmuir-Blodgett films, hydrophobic residues are turned towards the external surface, and the hydrophilic ones towards the glass substrate. But, in the opposite, when protein is obtained by lyophilization, the hydrophilic residues are orientated outsides. It seems possible to determine by XPS the nature of the residues which give to the protein its reactivity, since they are located at its external surface.

Surface modifications of hydroxyapatite ceramics in aqueous media.

Hydroxyapatite (HA) surfaces exposed, at room temperature, to various aqueous media of different compositions (distilled water, saline solution, cell culture media, saturated HA solution) have been studied by X-ray photoelectron spectroscopy (XPS) angular analysis and IR reflectance spectroscopy. An important decrease of the Ca/P atomic ratio of the surface layer was seen on all exposed surfaces, reaching 1, the Ca/P ratio of dicalcium phosphate dihydrate (DCPD) for the uppermost surface layer. Furthermore, HPO4(2-) ions were observed by XPS and IR. These chemical changes seem to be related to an equilibration process of the surface independent of the dissolution mechanism. Despite the Ca/P ratio observed, no specific phosphate ion environments, such as that of DCPD, were seen by IR.

Study of the mineral-organic linkage in an apatitic reinforced bone cement.

In order to increase mechanical properties of surgical cements, an apatitic filler has been linked to the polymethylmethacrylate (PMMA) matrix. We report here the study of the linkage between the mineral and organic components by a dielectric spectroscopy: Thermally Stimulated Current. First, the mineral-organic interface between apatitic-octocalcic phosphate and hydroxyethylmethacrylate (HEMA) has been investigated. Second, the filler-matrix interface between grafted apatite and PMMA has been examined. It has been shown that the filler is chemically linked to the matrix and stiffens the PMMA bone cement.

Calcium phosphate and polymer interfaces in orthopaedic cement.

In order to increase the mechanical properties and the bioactivity of surgical cement, the linkage of two monomers, namely hydroxyethylmethacrylate (HEMA) and methylmethacrylate (MMA), by copolymerization to a modified apatite has been studied. This linkage is obtained by grafting an organic molecule containing an ethylenic bond onto the apatite surface. These two studies have shown that after polymerization more than 70% of the modified apatite is irreversibly linked to the polymers. This linkage is due not to an adsorption but to the existence of a stable covalent bond between apatite and polymers. From these results, it should be possible to develop a new orthopaedic cement which will be more biocompatible and will have good mechanical properties.

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.