Surface mineralisation of hydroxyapatite in modified simulated body fluid (mSBF) with higher amounts of hydrogencarbonate ions

Mineralisation of pellets made of two types of hydroxyapatite (HA) (commercial Captal® R and synthesised in a laboratory) in a modified simulated body fluid (mSBF) having two initial concentrations of hydrogencarbonate ions (4.2 and 27 mM of dissolved NaHCO3) was studied by SEM, FTIR, EDX, and XRD techniques. The experiments were performed for 20 days at 37 °C and under two values of the solution pH: 6.5±0.1 and 7.4±0.1 adjusted by permanent bubbling of CO2. Etching of the synthesised HA and inertness of Captal® R HA were found in mSBF with the solution pH 6.5. The difference was due to presence of β-Ca3(PO4)2 in the former HA. Precipitation of a non-stoichiometric carbonateapatite onto the pellets made of both types of HA was found in mSBF with the solution pH 7.4. In the latter case, the newly precipitated crystals of carbonateapatite formed continuous layers of 1.5±0.1 μm (for mSBF contained 27 mM of the dissolved NaHCO3) and 0.9±0.1 μm (for mSBF contained 4.2 mM of the dissolved NaHCO3) thick onto the pellet surface.