The alkaline geopoly- mer synthesis conditions most likely give rise to an initially higher local pH inside the pellet pores [17] during the first stages
of release. Thus, a pH gradient, directed inwards from the pellet surface and reaching a maximum value immediately after pene- tration of the release media into the pellet, most likely exists. The higher pH inside the pellets allows for dissolution of the Alginate polymer, which starts to diffuse concomitantly with the drug. After the maximum pH gradient is reached, the pH inside the pellets is expected to decrease with time as the buffer protons diffuse into the pellet, reaching the dissolved alginate polymer that re-precipitates.
Fig. 2c and d shows the release of Zolpidem from the geopolymer pellets in pH 1 and pH 6.8, respectively. The release curve for PEG-h D is not shown in Fig. 2c since it almost completely overlays the release curve for PEG D. Only the samples from which the Zolpidem release was slower than for the Control sample were tested in pH 6.8. Thus, the samples containing PEG are not shown in Fig. 2d.
The two release medias were used to mimic the pH condition of the stomach (the pH in the stomach can be as low as 1) and gastrointestinal tract, respectively. The Control sample released its entire drug content within 4–5 h in pH 1, Fig. 2c, and about 70% of its drug content within 24h in pH 6.8, Fig. 2d, in accordance with what has been observed earlier for Zolpidem release from pure geopolymer samples [5]. As mentioned in the
The alkaline geopoly- mer synthesis conditions most likely give rise to an initially higher local pH inside the pellet pores [17] during the first stagesof release. Thus, a pH gradient, directed inwards from the pellet surface and reaching a maximum value immediately after pene- tration of the release media into the pellet, most likely exists. The higher pH inside the pellets allows for dissolution of the Alginate polymer, which starts to diffuse concomitantly with the drug. After the maximum pH gradient is reached, the pH inside the pellets is expected to decrease with time as the buffer protons diffuse into the pellet, reaching the dissolved alginate polymer that re-precipitates.Fig. 2c and d shows the release of Zolpidem from the geopolymer pellets in pH 1 and pH 6.8, respectively. The release curve for PEG-h D is not shown in Fig. 2c since it almost completely overlays the release curve for PEG D. Only the samples from which the Zolpidem release was slower than for the Control sample were tested in pH 6.8. Thus, the samples containing PEG are not shown in Fig. 2d.The two release medias were used to mimic the pH condition of the stomach (the pH in the stomach can be as low as 1) and gastrointestinal tract, respectively. The Control sample released its entire drug content within 4–5 h in pH 1, Fig. 2c, and about 70% of its drug content within 24h in pH 6.8, Fig. 2d, in accordance with what has been observed earlier for Zolpidem release from pure geopolymer samples [5]. As mentioned in the
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