NEW HYDROGELS IN PARTICLE AND FILM FORM FOR THE ENCAPSULATION AND CONTROLLED RELEASE OF BIOLOGICALLY ACTIVE COMPOUNDS

Abstract

The main objective of this research is to synthesize biocompatible gelatin-based hydrogels by cross-linking protein-free amino groups with aldehyde groups obtained by oxidation of sodium alginate, a dual cross-linking approach that incorporates both covalent and ionic bonds for propolis immobilization. The covalent bonds are formed by Schiff base bonds between the free amino groups (NH₂) of the lysine residues in the protein and the aldehyde groups (CHO) generated by the oxidation of sodium alginate using NaIO₄. Ionic bonds are created using Mg²⁺ ions. Hydrogel films were synthesized by varying the molar ratios of -CHO to -NH₂ under different pH conditions (3.7 and 5.5). The presence of aldehyde groups in oxidized sodium alginate (OSA) was confirmed by FTIR and NMR spectroscopy. The degree of oxidation was monitored for 48 hours and the effect of temperature was also studied. The results indicate that higher -CHO/-NH₂ molar ratios lead to an increase in the conversion index values for NH₂ groups, while a decrease in the swelling degree values was observed in media with pH values of 5.5 and 7.4. In addition, the effectiveness of encapsulation and release of propolis decreases as the degree of cross-linking of the hydrogel increases. In particular, UV irradiation enhanced the antioxidant activity of both free and encapsulated propolis. These results provide valuable insights into the design of biocompatible hydrogels for propolis immobilization, highlighting their potential for controlled release applications in the biomedical and pharmaceutical sectors.