A pH-sensitive microemulsion-filled gellan gum hydrogel encapsulated apigenin: Characterization and in vitro release kinetics

In this work, the incorporation of O/W microemulsion in gellan gum hydrogels was performed to prepare the composite hydrogel as the carrier of apigenin. In vitro release studies resulted that the composite hydrogels could control the drug release under acidic (pH 1.2) and weak alkaline conditions (pH 7.4). This was due to the increase of crosslinking degree under acidic medium and degradation under weak alkaline medium, observed by SEM technique. The FT-IR analysis further confirmed that the hydrogen ions (H+) under acidic conditions could diminish the electrostatic repulsion between the gellan gum molecules by offsetting the negative charge of carboxyl groups, promoting the formation of double helices. The in vitro release kinetics resulted that the release under acidic conditions was a Fickian diffusion-controlled mechanism. While the in vitro release under weak alkaline condition was erosion-controlled mechanism. In addition, the components of microemulsion have also an influence on the release behavior, which was related to the diameter distributions of microemulsion droplets and the hydrogen bond degrees between surfactants and polymers. As a result, the microemulsion-filled hydrogels could be a promising pH-controlled release system for oral delivery of hydrophobic drug.