About the Genetic Mechanisms of Apatites: A Survey on the Methodological Approaches

Abstract

Apatites are properly considered as a strategic material owing to the broad range of their practical uses, primarily biomedical but chemical, pharmaceutical, environmental and geological as well. The apatite group of minerals has been the subject of a huge number of papers, mainly devoted to the mass crystallization of nanosized hydroxyapatite (or carboapatite) as a scaffold for osteoinduction purposes. Many wet and dry methods of synthesis have been proposed. The products have been characterized using various techniques, from the transmission electron microscopy to many spectroscopic methods like IR and Raman. The experimental approach usually found in literature allows getting tailor made micro-and nano-crystals ready to be used in a wide variety of fields. Despite the wide interest in synthesis and characterization, little attention has been paid to the relationships between bulk structure and corresponding surfaces and to the role plaid by surfaces on the mechanisms involved during the early stages of growth of apatites. In order to improve the understanding of their structure and chemical variability, close attention will be focused on the structural complexity of hydroxyapatite (HAp), on the richness of its surfaces and their role in the interaction with the precursor phases, and in growth kinetics and morphology.

A Study of Thermal Stability of Hydroxyapatite

“…As seen from the absorption spectra of the sampl after in situ heat treatment, the intensity of the stretching and libration vibrations of t OH group is much less than that after heating in the furnace. It should also be noted that in the PXRD patterns of both the heated and cooled sam ples, there are no reflections indicating the change of the hexagonal space group to t monoclinic P21/b as was observed by other authors [9]. A splitting of reflections, whi was reported by Alberius et al and Gross et al [35,36], was not observed, either.…”

“…HA is produced in the form of an ionic crystal, either of hexagonal (P6 3 /m) or monoclinic (P2 1 /b) symmetry, depending on the conditions [1,8,9]. The main difference between the hexagonal and the monoclinic HA is the orientations of the hydroxyl groups located in the channel formed by calcium cations [9]. In monoclinic HA, all of the OH groups in a given column are pointed in the same direction, and the direction reverses in the next column.…”

“…In addition, the carbonate ions or other impurity ions used for preparing HA can be incorporated into its structure during the precipitation process [1,12], thus affecting the values of the lattice constants [4]. [3,9,11] Due to its chemical similarity to the mineral component of human bone and dental tissue, hydroxyapatite is widely used in medicine, particularly, as filler material to repair bone defects, to produce ceramic implants or coatings on metal implants, for the preparation of bone cements, as drug delivery systems, and as an additive in toothpastes and cleaning means [11,13,14]. In addition, synthetic HA is used as a filler for column chromatography, as gas sensors, catalysts, and sorbents [11,15].…”

Modulated Monoclinic Hydroxyapatite: The Effect of pH in the Microwave Assisted Method

“…For instance, H. Morgan et al obtained monoclinic HAp with a hexagonal shape at 900 • C [29], and T. Ikoma et al followed a wet methodology and heated up to 1200 • C to induce the monoclinic phase. On the other hand, L. Pastero et al used wet synthesis and citrate as surfactant to preferentially obtain monoclinic hydroxyapatite at 135 • C [30].…”

Editorial for Special Issue “Nucleation of Minerals: Precursors, Intermediates and Their Use in Materials Chemistry”

“…Several papers of this Minerals special issue deal with calcium phosphate-the most important biomineral for the human race. Pastero et al [16] provide a review of the genetic mechanisms of apatite, paying close attention to the structural complexity of hydroxyapatite, the richness of its surfaces and their role in interactions with precursor phases regarding growth kinetics and morphology. Ibsen et al [17] study the impact of pyrophosphate on apatite formation by synchrotron-based in situ X-ray diffraction, revealing a strong inhibition of apatite nucleation and growth.…”