Drug Sustain-release Property of Glass Ionomer Cement Containing Nano-porous Silica

Objectives: Glass ionomer cement (GIC) have fluorine sustained-release property. Though it can prevent becoming dental caries, that is not enough. Therefore, we have focused on nano-porous silica (NPS) attempting to develop novel GIC gradually releasing drug in addition fluorine. In this study, we used rhodamine B (RhB), which is water-soluble dye, as a model drug and evaluated sustained-release property of GIC containing NPS.
Methods: NPS (SIGMA-ALDRICH, St. Louis, MO, USA) had spherical shape with a diameter 3 µm and numerous cavities that were approximately 4 nm in diameter. The NPS were mixed into GIC at 10 wt% concentration. Then specimens (GIC-NPS, f10 x 1 mm) were prepared by the mixing. The GIC-NPS were immersed into 1 wt% RhB aqueous solutions at 37°C for 24h. Obtained GIC-NPS was immersed into distilled water at 37°C for 24h. The pellets removed to a fresh water every day for 28 days. Amount of released RhB into the supernatant were determined using UV-vis. spectrophotometer. After 28 days, the GIC-NPS was immersed into RhB solutions again for recharge of dyes. Then the release behaviour was estimated in the same manner.
Results: The model drug release behaviour was determined based on absorption spectrometry. When the GIC-NPS were immersed in water, the supernatant indicated characteristic absorption spectra, which was assigned to RhB. Though the intensity decrease gradually depending on the immersion time, the spectrum can be detected even after 4 weeks immersion. After dye-recharged process, they also indicated similar behaviour more than 3 weeks. In contrast, specimens without NPS showed different behaviour. Their peak disappeared within a week. These results suggested that NPS could capture and gradually release model drug.
Conclusions: GIC-NPS has excellent sustained-release property of model drug because NPS can capture and release drugs with their nanostructures.