Preparation and evaluation of mixed alginate-cyclodextrin hydrogels: From physicochemical, thermotropic to swelling characterization

The aim of this study is to develop hydrogel beads with the addition of cyclodextrins into a sodium alginate matrix and examine their swelling properties in different pH conditions. To achieve this, Methyl-β-Cyclodextrin (M-β-CD) and Hydroxypropyl-β-Cyclodextrin (HP-β-CD) were mixed with sodium alginate solution to form hydrogel beads. The formation of these beads was achieved at two different dropping distances (15 cm and 25 cm), and their swelling behavior was evaluated in two pH environments: SGF (simulated gastric fluid, pH 1.2) and SIF (simulated intestinal fluid, pH 6.8). The thermotropic behavior of the prepared alginate-based beads was analyzed using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). Scanning Electron Microscopy (SEM) was employed to evaluate the impact of the preparation method and the presence of different types of cyclodextrins (CDs) on the beads' morphological characteristics. Results indicated that the addition of CDs had a substantial impact on the beads’ swelling behavior and morphology, with HP-β-CD beads demonstrating the highest disintegration rate in SIF, mostly due to greater hydrophilicity and matrix interactions. The beads with CDs that were prepared at higher dropping distance exhibited increased porosity, enhancing water absorption. This study highlights the impact of CDs’ coexistence on the pH-responsiveness of alginate-based hydrogels, underscoring their potential as delivery platforms for controlled drug release systems.