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The substitution of tris/HCl buffer by CO(2)/HCO(3)(-) buffer in inorganic plasma was studied. An appropriate gas mixture of CO(2)/N(2) was continuously bubbled in Kokubo's SBF solution prepared without addition of Tris/HCl. This method enables buffering the solution within the 7.3-7.4 pH interval and, at the same time, reaching a HCO(3)(-) concentration between 24 and 27 mmol dm(-3), which are the normal concentrations reported for blood plasma. Mineralisation studies on calcium phosphate ceramics using this solution showed that, in the presence of such hydrogencarbonate concentrations, the formation of a mineralisation layer on the ceramic occurs via a carbonated octacalcium phosphate, that evolves to carbonated hydroxyapatite. The results suggest that mineralisation studies in this new carbonate-containing simulated inorganic plasma mimic biomineralisation more closely than traditional SBF.

Glasses and glass ceramics of fluorapatite-anorthite (eutectic composition) were produced and characterized in order to evaluate their potential application in biomedicine. Bio-reactivity was determined by in vitro tests by immersion of powders in simulated plasma liquids as well as by in vivo experiments by implantation in rabbits. According to the results, the investigated materials are bio-acceptable since no toxic or other harmful evidence was detected. Glass-ceramics showed remarkable inertness, whereas glasses spontaneously dissolved in SBF and after 1 week moderate formation of apatite was observed, that however ceased within a month.

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.

The surface reactivity of glasses belonging to the (mol%) 31SiO2-11P2O5-(58-x)CaO-xMgO series, with x ranging from 0 to 32, was studied in Kokubo's simulated body fluid (SBF). Scanning electron microscopy, inductively coupled plasma spectroscopy and Fourier transform infrared spectroscopy were used to characterise the glass surface and the SBF compositional changes. All glasses develop surface layers rich in silica and calcium phosphate. An increasing surface activity with increasing MgO/CaO ratio was observed. In a previous investigation using magic-angle spinning nuclear magnetic resonance it was found that there is an increasing abundance of Q0 species in the glass structure with increasing MgO content. The present work shows that, when immersed in SBF, Q0-rich glasses are easily leached to form a silica gel layer. It is concluded that MgO in the glass indirectly improves the early stages of mineralisation by favouring Q0 speciation. This mechanism plays an important role in glass bioactivity.

A glass of nominal composition (wt%) 40.0 CaO-34.5 SiO2-16.5 P2O5-8.5 MgO-0.5 CaF2 has been obtained (G13). The glass showed in vitro bioactivity evidenced by the formation on its surface of a calcium phosphate-rich layer when soaked in a solution with ionic composition analogous to human plasma. By thermal treatments of G13, a glass-ceramic (GC13) containing apatite, diopside, althausite and akermanite as crystalline phases was developed. GC13 as-made did not show in vitro bioactivity. However, after chemical treatment of GC13 with 1 M HCl (GC13-HCl), the in vitro studies showed the formation of an apatite-like layer covering certain areas of the material surface. The influence of both chemical and morphological factors on the in vitro bioactivity has been studied.

A glass of nominal composition (wt%) 17.25 MgO-52.75 3CaO.P2O5-30 SiO2 and a glass-ceramic obtained from it showed surface modifications when immersed in an acellular medium having a composition similar to that of human blood plasma. A (Ca, P)-rich layer, with an approximate Ca/P atomic ratio of 1.7, identified as hydroxyapatite, developed on both samples. The precipitated film on the glassy sample was weakly bonded, whereas that formed on the glass-ceramic was strongly adherent. The apatite precipitated during the in vitro tests on both samples grew as a needle-like structure with crystals about 150-200 nm long and 50-70 nm thick, as measured on specimens soaked for 1 month in the simulated body fluid (SBF). The presence of calcium and phosphate ions in the SBF contributed to the precipitation of the (Ca, P)-rich layers on both specimens.