Quantifying the Effect of Adding Alkaline Phosphatase Enzyme to Silicate/Phosphate Glass Mixtures to Enhance Bone Regeneration

Abstract

Bioactive silicate glass-based (PerioGlas®) has been previously used to enhance periodontal bone regeneration. However, the degradation of this glass in the body fluid generates a high pH (>8) which may enhance the growth of periodontopathic bacteria, such as Porphyromonas gingivalis (P. gingivalis) thereby inhibiting osteoblastic activity. The aim of this study was to: (i) develop a mixture of a phosphate and silicate glass to produce a more neutral pH environment where the alkaline pH arising from the bioactive silicate glass can be offset by the acidity of phosphate glass, (ii) whether the alkaline phosphatase enzyme (ALP) when added to the silicate/phosphate glass mixture can enzymatically hydrolyse the Q2 metaphosphate chains to release Q0 orthophosphate species that can be used in forming apatite and bone mineralization. For this purpose, nine compositions of bioactive silicate/ phosphate glass-mixtures were prepared. The glass bioactivity was performed by immersing the prepared glass mixtures in ALP containing Tris buffer solution. The pH change in solutions was measured as a function of time. The glass mixtures degradation and apatite formation were investigated by 31P Solid and 31P Solution Nuclear Magnetic Resonance (NMR) spectroscopies. The results showed that the pH behaviour was modulated by immersing the glass-mixtures in buffered solutions. Solid and Solution NMR revealed that the terminal Q1 species belonging to the Q2-metaphosphate chains was hydrolysed by the ALP and converted into a Q0 orthophosphate species. In conclusion, the glass mixtures regulated the pH through its degradation stepwise on immersion. The output of the NMR spectra significantly supported the enzymatic degradation of glass mixtures with ALP enabling apatite precipitation for new bone formation. The concept of using silicate/phosphate glass mixtures with ALP is innovative and pioneering technology, suggesting its potentiality to develop new biomedical materials for different applications.