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.

No abstract

The environment of carbonate ions in bones of different species (rat, rabbit, chicken, cow, human) was investigated by Fourier Transform Infrared Spectroscopy (FTIR) associated with a self-deconvolution technique. The carbonate bands in the v2 CO3(2-) domain show three components which were identified by using synthetic standards and different properties of the apatitic structure (ionic affinity for crystallographic locations, ionic exchange). The major component at 871 cm-1 is due to carbonate ions located in PO4(3-) sites (type B carbonate). A band at 878 cm-1 was exclusively assigned to carbonate ions substituting for OH-ions in the apatitic structure (type A carbonate). A band at 866 cm-1 not previously observed was shown to correspond to a labile carbonate environment. The intensity ratio of type A to type B carbonate appears remarkably constant in all bone samples. The 866 cm-1 carbonate band varies in its relative intensity in different species.

The processes of bone resorption and formation are tightly governed by a variety of systemic and local regulatory agents. In addition, minerals and trace elements affect bone formation and resorption through direct or indirect effects on bone cells or bone mineral. Some trace elements closely chemically related to calcium, such as strontium (Sr), have pharmacological effects on bone when present at levels higher than those required for normal cell physiology. Indeed, strontium was found to exert several effects on bone cells. In addition to its antiresorptive activity, strontium was found to have anabolic activity in bone, and this may have significant beneficial effects on bone balance in normal and osteopenic animals. Accordingly, strontium has been thought to have potential interest in the treatment of osteoporosis. This review summarizes the mechanisms of action of strontium on bone cells, the evidence for its beneficial effects on bone mass in vivo, and its potential therapeutic effects in osteopenic disorders.

HistoryThe structure of the Ca-P solid phase in bone was first identified by deJong in 1926 as a crystalline calcium phosphate similar to geological apatite by chemical analyses and, most importantly, by X-ray diffraction [1]. The X-ray diffraction data was confirmed a few years later [2].These findings initiated a flurry of research on a more detailed chemical composition and crystal structure of both geological and synthetic apatites and of bone mineral, initially carried out principally by geologists, crystallographers and chemists, but later by biochemists and physiologists because of the clear potential of this new information to shed light on the biological and physiological functions of bone mineral and as indicators of disorders of the skeletal system. It soon became clear that there were significant structural and chemical compositional differences between the many different geological hydroxyapatites, synthetic hydroxyapatites, and the apatite crystals found in bone and related skeletal tissues in addition to the very large size of the geological and many of the synthetic apatite crystals, compared with the extremely small particle size of bone mineral.Further studies were directed in roughly three avenues: continued more careful and complete analytical compositional data of bone mineral, from which it was clearly established that the chemical composition of bone crystals in many ways did not correspond to the chemical compositions of stoichiometric hydroxyapatite. Indeed, the bone crystals were found to contain significant and varying amounts of carbonate and HPO 4 ions. Much later it was discovered by a variety of techniques, including solid state NMR [3], Raman spectroscopy [4], and inelastic

International audienceNanocrystalline apatites play an important role in biomineralisation and they are used as bioactive biominerals for orthopaedic applications. One of the most interesting characteristics of the nanocrystals, evidenced by spectroscopic methods, is the existence of a structured surface hydrated layer, well developed in freshly formed precipitates, which becomes progressively transformed into the more stable apatitic lattice upon ageing in aqueous media. The hydrated layer is very fragile and irreversibly altered upon drying. Several routes leading to different apatite compositions are found in biological systems. The loosely bound ions of the hydrated layer can be easily and reversibly substituted by other ions in fast aqueous ion exchange reactions. These ions can either be included in the growing stable apatite lattice during the ageing process or remain in the hydrated layer. The adsorption properties of nanocrystals appear to be strongly dependent on the composition of the hydrated layer and on ageing. The surface reactivity of the apatite nanocrystals can play a part in different biomaterials and could explain the setting reactions of biomimetic calcium phosphate cements and the possibility of obtaining adherent nanocrystalline coatings on different substrates

In order to investigate the possible existence in biological and poorly crystalline synthetic apatites of local atomic organizations different from that of apatite, resolution-enhanced, Fourier transform infrared spectroscopy studies were carried out on chicken bone, pig enamel, and poorly crystalline synthetic apatites containing carbonate and HPO4(2-) groups. The spectra obtained were compared to those of synthetic well crystallized apatites (stoichiometric hydroxyapatite, HPO4(2-)-containing apatite, type B carbonate apatite) and nonapatitic calcium phosphates which have been suggested as precursors of the apatitic phase [octacalcium phosphate (OCP), brushite, and beta tricalcium phosphate and whitlockite]. The spectra of bone and enamel, as well as poorly crystalline, synthetic apatite in the upsilon 4 PO4 domain, exhibit, in addition to the three apatitic bands, three absorption bands that were shown to be independent of the organic matrix. Two low-wave number bands at 520-530 and 540-550 cm-1 are assigned to HPO4(2-). Reference to known calcium phosphates shows that bands in this domain also exist in HPO4(2-)-containing apatite, brushite, and OCP. However, the lack of specific absorption bands prevents a clear identification of these HPO4(2-) environments. The third absorption band (610-615 cm-1) is not related to HPO4(2-) or OH- ions. It appears to be due to a labile PO4(3-) environment which could not be identified with any phosphate environment existing in our reference samples, and thus seems specific of poorly crystalline apatites. Correlation of the variations in band intensities show that 610-615 cm-1 band is related to an absorption band at 560 cm-1 superimposed on an apatite band. All the nonapatitic phosphate environments were shown to decrease during aging of enamel, bone, and synthetic apatites. Moreover, EDTA etching show that the labile PO4(3-) environment exhibited a heterogeneous distribution in the insoluble precipitate.

The environment of CO3(2-) ions in the bone mineral of chickens of different ages and in bone fractions of different density have been investigated by resolution-enhanced Fourier Transform Infrared (FTIR) Spectroscopy. Three carbonate bands appear in the upsilon 2 CO3 domain at 878, 871, and 866 cm-1, which may be assigned to three different locations of the ion in the mineral: in monovalent anionic sites of the apatitic structure (878 cm-1), in trivalent anionic sites (871 cm-1), and in unstable location (866 cm-1) probably in perturbed regions of the crystals. The distribution of the carbonate ions among these locations was estimated by comparing the intensities of the corresponding FTIR spectral bands. The intensity ratio of the 878 and 871 cm-1 bands remains remarkably constant in whole bone as well as in the fractions obtained by density centrifugation. On the contrary, the intensity ratio of the 866 cm-1 to the 871 cm-1 band was found to vary directly and decreased with the age of the animal. In bone of the same age, the relative content of the unstable carbonate ion was found to be highest in the most abundant density centrifugation fraction. A resolution factor of the CO3(2-) band (CO3 RF) was calculated from the FTIR spectra which was shown to be very sensitive to the degree of crystallinity of the mineral. The crystallinity was found to improve rapidly with the age of the animal. The CO3 RF in the bone samples obtained by density centrifugation from bone of the same animal was found to be essentially constant.(ABSTRACT TRUNCATED AT 250 WORDS)