Calcium Phosphate Species Research Articles

Synthesis of Si, Mg substituted hydroxyapatites and their sintering behaviors

Si, Mg-substituted hydroxyapatites, alone and co-substituted, have been prepared to obtain biomaterials having an improved biocompatibility. From FT-IR, XRD and ICP analyses, it was confirmed that single phases of hydroxyapatite substituted by Si alone or co-substituted by Si, Mg. The XRD data indicated the absence of extra phases related to silicon and magnesium oxide or other calcium phosphate species. Si-substituted hydroxyapatite of up to 2 wt% for Si and Si, Mg co-substituted hydroxyapatite of 1 wt% for the each ion keep their original structures intact for the sintering temperatures of up to 1200°C. However, it is observed that ion substitutions by an amount higher than the above ratios for each hydroxyapatite lead to destabilization of original structures of the hydroxyapatite and to the production of tricalcium phosphate and calcium phosphate silicate phases when the samples were sintered at 1100°C or higher.

The chemistry of enamel caries.

The chemical changes which occur during the process of carious destruction of enamel are complex due to a number of factors. First, substituted hydroxyapatite, the main component of dental enamel, can behave in a very complex manner during dissolution. This is due not only to its ability to accept substituent ions but also to the wide range of calcium phosphate species which can form following dissolution. In addition, the composition, i.e., the extent of substitution, changes throughout enamel in the direction of carious attack, i.e., from surface to interior. Both surface and positively birefringent zones of the lesion clearly illustrate that carious destruction is not simple dissolution. Selective dissolution of soluble minerals occurs, and there is the probability of reprecipitation. The role of fluoride here is crucial in that not only does it protect enamel per se but also its presence in solution means that rather insoluble fluoridated species can form very easily, encouraging redeposition. The role of organic material clearly needs further investigation, but there is the real possibility of both inhibition of repair and facilitation of redeposition. For the future, delivering fluoride deep into the lesion would appear to offer the prospect of improved repair. This would entail a delivery vehicle which solved the problem of fluoride uptake by apatite at the tooth surface. Elucidation of the role of organic material may also reveal putative mechanisms for encouraging repair and/or protecting the enamel mineral.

The Preparation of Spherical Calcium Phosphate Fine Particles Using an Emulsion Liquid Membrane System

Calcium phosphate fine particles were prepared by using an emulsion liquid membrane (ELM, water-in-oil-in-water (W/O/W) emulsion) system, consisting of Span 83 (sorbitan sesquioleate) as surfactant and VA-10 (2-methyl-2-ethyl heptanoic acid) as extractant (cation carrier). Calcium ions were extracted from the external water phase and stripped into an internal water phase containing phosphate anions, to form calcium phosphate particles. The submicrometer-sized spherical calcium phosphate particles obtained were characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrophotometry and thermal analysis (TG-DTA). The characterization revealed that the fine particles obtained were calcium-deficient apatite in combination with various other calcium phosphate species. Decomposition from hydroxyapatite to β-TCP (whitlokite) occurred at 973 K, and thermal treatment above 1073 K produced a β-TCP and CaO composite. The freeze−thaw demulsification method yielded well-defined spherical particles of 0.5−20 μm (mostly smaller than 10 μm) in diameter; the shape and size of the internal water droplets is likely to influence the morphology of the formed particles.

Surface characterization of C/Ti-6Al-4V coating treated with ion beam

Surface of titanium alloy (Ti-6Al-4V) has been modified by ion beam mixing of thin C film. X-ray photoelectron spectroscopy analysis showed that after mixing, the surface film consists essentially of a Ti compound containing (Ti, O and C), TiO 2, Ti and C contamination. The composition of the surface modified film determined by Rutherford backscattering spectrometry is approximately Ti 0.5O 0.3C 0.2 and its thickness is about 200 nm. After three months immersion in a simulated body fluid, the growth of calcium phosphate species containing both HPO 4 − and H 2PO 4 − (probably CaHPO 4 and Ca(HPO 4) 2) have been observed. Titanium is found to be essentially composed of the Ti compound after immersion suggesting that both metallic Ti and TiO 2 have dissolved.

Co-crystallization of cholesterol and calcium phosphate as related to atherosclerosis

Calcification of atherosclerotic plaques occurs very frequently and aggravates the disease. In biological systems, epitaxial relationships between crystal structures may be important in nucleating the deposit of a solid phase. The biologically preferred calcium phosphate species, apatite, and cholesterol crystal have structurally compatible crystallographic faces which allow epitaxial growth of one crystal upon another. The present study describes a new approach to explore, in vitro, the crystallization processes of calcium phosphate (CaP) with cholesterol (CS) and cholestanol (CN) which are related to atherosclerosis. Aqueous solutions containing calcium and phosphate ions or CaP crystals as hydroxyapatite were added into saturated ethanolic solutions of CS or CS and 10% CN. After precipitation, crystals were collected and analyzed by nuclear magnetic resonance (NMR), infra-red (IR), X-ray, scanning electron microscope (SEM-LINK), differential scanning calorimeter (DSC) and atomic absorption. The principal result is the well-formed crystals precipitation when an aqueous solution and CaP seed crystals were added to saturated solutions of CS and 10% CN. Cholesterol-cholestanol dihydrate (CC2W) crystals precipitated in the presence of CaP seeds were compared to the CC2W crystals obtained without the mineral compound. The results of this comparison indicate a special link between crystals of CaP and CC2W, and support the epitaxial relationship between the two kinds of crystals. The potential of CC2W crystals to be precipitated by CaP seed crystals prove likewise the possible significant role of the cholestanol metabolite in the process of cholesterol crystallization and calcification in the arteries.

Some physicochemical phenomena affecting demineralization and remineralization: a review.

Abstract— The processes of dental caries and remineralization obey the same thermodynamic laws. The total repair of an early lesion is possible in vitro but repair in vivo is complicated by additional parameters often introduced predominately by lack of oral hygiene and improper diet. This paper discusses the behaviour of calcium phosphate species in biological systems and how these minerals react with changes in solution composition. The early lesion is reviewed from this viewpoint and remineralization is discussed.

Calcium-carbonate–phosphate surface complex in calcareous systems

The interactions between soluble orthophosphates and lime (CaCO3) have been extensively studied because of the frequent occurrence of soil systems rich in CaCO3 and the dominant effect of calcium carbonate on phosphate solubility. Several investigators have suggested that in these systems chemically defined calcium phosphate species are precipitated. Cole and Olsen1 found that the solubility of phosphate in calcareous soils seems to be controlled by a di-calcium phosphate (DCP) solid phase, although the solubility product inferred (2.89 × 10−9) is significantly less than that measured2 for DCP (2 × 10×7). Similar results have been reported for the interaction between fish-pond sediments and the aqueous phase3. On the other hand, Stum and Leckie4 have suggested that the solubility of phosphate in calcareous systems may be controlled by the chem-isorption of phosphate on CaCO3 particles, with the formation of amorphous calcium phosphates3 or of surface complexes.4 We now describe experiments which argue for the formation of a surface complex of calcium-carbonate–phosphate with well defined chemical composition.