Mineralisation of two phosphate ceramics in HBSS: role of albumin

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Abstract

The role of albumin in the mineralisation process of commercial hydroxyapatite (HAp) and synthesised biphasic (HAp-tricalcium phosphate) ceramics in a bufferless simulated inorganic plasma (HBSS) was investigated by conventional in vitro tests and static and dynamic wettability measurements. Albumin was either pre-adsorbed or solubilised in HBSS. It was found that calcium complexation by albumin plays a key role in early mineralisation kinetics, so that mineralisation is favoured when albumin is pre-adsorbed and hindered when it is dissolved in HBSS. In the biphasic ceramic this picture is complicated by the fact that albumin, in solution, seems to promote the dissolution of tricalcium phosphate, and simultaneously compete for calcium with the ceramic. It also appears that albumin has a stabilising effect of octacalcium phosphate present in deposits on commercial HAp. The same effect may be present in the case of the biphasic ceramic, at earlier mineralisation times, when octacalcium phosphate appears as a precursor of HAp. Octacalcium phosphate formation on commercial apatite is accompanied by carbonate substitution in phosphate positions.

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Resolution-enhanced Fourier transform infrared spectroscopy study of the environment of phosphate ion in the early deposits of a solid phase of calcium phosphate in bone and enamel and their evolution with age: 2. Investigations in the nu3PO4 domain.

C Rey-Joly, M Glimcher, Leonard Collins … (1991)

Resolution-enhanced Fourier Transform Infrared (FTIR) spectra of early mineral deposits in enamel and bone show bands at 1020, 1100, 1110, 1125, and 1145 cm-1 in the nu3PO4 domain which do not belong to well crystallized stoichiometric hydroxyapatite. Bands at 1020 and 1100 cm-1 have been shown to occur in nonstoichiometric apatites containing HPO4(2-) ions and the weak band at 1145 cm-1 has been assigned to HPO4(2-) ions. Though the bands at 1110 and 1125 cm-1 have not been found in any well crystallized apatite, they are present in newly precipitated apatite. These latter bands disappear progressively during maturation in biological as well as synthetic samples, and partial dissolution of synthetic apatites shows that they belong to species that exhibit an inhomogeneous distribution in the mineral, and that are the first to be solubilized. Comparison of the FTIR spectra of biological apatites with those of synthetic, nonapatitic-containing phosphate minerals shows that the presence of these bands does not arise from nonapatitic, well-defined phases; they are due to the local environment of phosphate ions which may possibly be loosely related or perhaps unrelated to the phosphate groups present in the well-crystallized nonapatitic calcium phosphates. Resolution-enhanced FTIR affords a very precise characterization of the mineral phases which may be very useful in characterizing pathological deposits of Ca-P mineral phases.