Biomedical subjects

E Bres

Publications and source records attributed to E Bres.

5 recordsLinked to original sources

PubMed2001

Structure and substitutions in fluorapatite.

Fluorapatite, Ca10(PO4)6F2. is a widely spread form of calcium phosphate present particularly in biological material. Human hard tissues contain crystals structurally related to apatite. Fluoride can be found in various natural sources and is also used for its beneficial action in caries prevention. Fluorapatite belongs to the spatial group P6(3/m) (C(6h)2) and consists of 3 ions: F-, Ca2+, PO4(3-). In the present paper, we have carried out a crystallographic study of the fluorapatite structure and of the changes induced by the substitutions. The fluorapatite structure and the presence of a large number of ionic bonds make fluorapatite a very suitable host for many substituents, some of them harmless for the human organism, some not. According to the substitution site, we can describe four types of substitution. The F- substitution, also called Type A substitution, is the main one, and the best known. Only the Ca2+ substitution implies changes in the crystal structure. However, some questions remain, in particular for the PO4(3-) substitution, which is the main substitution present in the biological calcium phosphates.

Journal Article↗

PubMed1998

Basic fibroblast growth factor adsorption and release properties of calcium phosphate.

Basic fibroblast growth factor (bFGF) is well known as a potent angiogenic factor playing a crucial role in wound-healing processes. Apatitic substrates such as hydroxyapatite and carbonated apatite (CA) could be potential carriers of growth factors because of their physicochemical similarities to bone mineral. These materials have been compared for their bFGF adsorption and release properties. The adsorption of the growth factor was higher on carbonated apatite than on hydroxyapatite, probably owing to environments with labile nonapatitic CO3(2-) and HPO4(2-) groups, along with a higher specific surface area which gives the CA a higher surface reactivity. These environments can be exchanged very rapidly, leading to the release of bFGF. The controlled release of adsorbed growth factor from carbonated apatite could provide means of improving bone healing in the future.

Adsorption↗

PubMed1998

MicroRaman spectral study of the PO4 and CO3 vibrational modes in synthetic and biological apatites.

The carbonate and phosphate vibrational modes of different synthetic and biological carbonated apatites were investigated by Raman microspectroscopy, and compared with those of hydroxyapatite. The nu1 phosphate band at 960 cm-1 shifts slightly due to carbonate substitution in both A and B sites. The spectrum of type A carbonated apatite exhibits two nu1 PO43- bands at 947 and 957 cm-1. No significant change was observed in the nu2 and nu4 phosphate mode regions in any carbonated samples. The nu3 PO43- region seems to be more affected by carbonation: two main bands were observed, as in the hydroxyapatite spectrum, but at lower wave numbers. The phosphate spectra of all biominerals apatite were consistent with type AB carbonated apatite. In the enamel spectrum, bands were observed at 3513 and at 3573 cm-1 presumably due to two different hydroxyl environments. Two different bands due to the carbonate nu1 mode were identified depending on the carbonate substitution site A or B, at 1107 and 1070 cm-1, respectively. Our results, compared with the infrared data already reported, suggest that even low levels of carbonate substitution induce modifications of the hydroxyapatite spectrum. Increasing substitution ratios, however, do not bring about any further alteration. The spectra of dentine and bone showed a strong similarity at a micrometric level. This study demonstrates the existence of acidic phosphate, observable by Raman microspectrometry, in mature biominerals. The HPO42- and CO32- contents increase from enamel to dentine and bone, however, these two phenomena do not seem to be correlated.

Apatites↗

PubMed1998

[Long-term ultrasonographic evaluation of teflon paste compression in children endoscopically treated for vesicoureteral reflux. Preliminary report].

UNLABELLED: The endoscopic treatment of vesicoureteral reflux with transurethral injection of teflon into submucosal part of ureter was performed for the first-time in 1981. Unfortunately this method of treatment was not accepted because of the teflon migration (proved in experimental therapy) into different organs (lungs, brain, lymphatic nodules). Defining the quantity changes of teflon in children treated with this method in long-term follow-up (minimum 8 years). The ultrasonography was performed in 20 cases of female children with diagnosed vesicoureteral reflux and treated in 1987-1990 by injection of teflon (in age from 1 to 10). There were 33 ureters treated. The vertical and transversal sizes and the area of teflon were defined and compared with ultrasonographic investigation performed early after injection. In 14 ureters (43%) the sizes of teflon mass in submucosal part of the ureter were the same as just after injection. In 12 ureters (36%) the mass was considerably lower and in 7 cases (21%) there was no teflon in the injection place. The changes of teflon mass quantity were noticeable in 57%. CONCLUSIONS: The reduction or loss of teflon mass injected into submucosal part of ureter in children treated endoscopically for vesicoureteral reflux was demonstrated in high percentage of cases. There is a possibility that teflon was excreted into bladder through mucosa perforated by a needle during injection or because of later perforation of mucosa. This hypothesis is not so probable--early postoperative ultrasound controls showed right quantity of teflon mass. There is no proof that the loss of mass is caused by migration. This situation has to be taken into consideration but the appearance of symptoms is rather not probable (quantity of injected mass varies 0.1-1 ml).

Child↗

PubMed1997

Infrared and Raman microspectrometry study of fluor-fluor-hydroxy and hydroxy-apatite powders.

Visible Raman and infrared microspectrometry studies performed on fluorapatite and hydroxyapatite powders have shown similar results. Small modifications of the nu2 and nu4 PO(3-)4 tetrahedra bending modes are observed. A small frequency shift of the nu1 mode and modifications on the nu3 mode region accompanied with a simplification of the hydroxyapatite and fluorapatite respective spectra from seven to four bands were observed. A broad and weak band which could be attributed to the Ca-F bond is detected at 311 cm(-1) on the Raman fluorapatite spectra. The phosphate vibration modes are little disturbed by fluoride substitution. This could indicate that phosphate groups interact strongly between themselves and weakly with substituted atoms (i.e. hydroxyle and fluoride atoms). Whatever crystallographic model is considered, the number of bands observed is always lower than the number of calculated ones, even for hydroxyapatite, whose symmetry is lower than that of fluorapatite.

Journal Article↗