Monitoring of the dissolution/precipitation behavior of bioglass with simulated body fluid buffered by HEPES

This research work investigates a 7-day interaction of bioactive glass in the form of grit with simulated body fluid with addition of HEPES buffer (SBF+H). The standard fluid buffered by TRIS (SBF+T) and unbuffered (SBF-Ø) were used for comparison. To understand the process more precisely, the material and the leachates were analyzed at hourly (1H, 2H, 4H) and daily (1D, 2D, 3D, 4D, 7D) intervals. During the static in vitro test the weight and specific surface area of the materials were measured and the surface and volume changes of the material character/composition were monitored by SEM/EDS and XRD. Samples of solution leachates were collected at regular intervals to determine concentrations of calcium, silicon and (PO₄)³⁻ and to measure pH. After exposure in SBF+T and SBF+H a new crystalline layer of hydroxyapatite formed on the material surface. The material exposed to SBF+H dissolved less than the one exposed to SBF+T but the hydroxyapatite layer on its surface grew faster. The material exposed only to SBF-Ø without any buffer dissolved much less, while the ions released into the solution very rapidly re-precipitated on the surface. As a result, three amorphous layers containing Si, Ca and P with different thicknesses were gradually formed on the surface. Results of material and solution analyses have clearly shown that both HEPES and TRIS buffers have a significant effect on the formation of hydroxyapatite on the surface of bioactive glass. The behavior of the HEPES buffer with highly bioactive bioglass is very similar to that of the TRIS buffer.