Formulation of Alginate–Gelatin Hydrogels within a Circular Economy Framework: Controlled Release of Grape Skin Extract via Gelatin Content Modulation

Abstract

Hydrogels, as cross-linked polymer networks, are increasingly utilized in biomedical applications due to their high water absorption, biocompatibility, and capability to deliver bioactive substances. Compared to synthetic hydrogels, natural polymers such as alginate and gelatin provide advantages including biodegradability, low toxicity, and the formation of stable matrices suitable for biomedical use. Grape skins from the Šumadija region in Serbia, a byproduct of winemaking, are abundant in polyphenolic compounds with potent antioxidant and anti-inflammatory effects, making them suitable for incorporation into bioactive hydrogel systems. In this study, alginate–gelatin hydrogels were prepared and loaded with grape skin extract (GSE) to evaluate their physicochemical characteristics and in vitro release behavior. Three formulations with different alginate-to-gelatin ratios (3:1, 3:2, and 1:1) were produced, mixed with GSE (8 mg/mL), frozen, and cross-linked with CaCl₂. Organoleptic assessment confirmed uniform, coherent gels, with color imparted by the extract. In vitro release studies in PBS (pH 7.4, 37 °C) demonstrated a biphasic release, with an initial rapid phase during the first 5–10 h followed by sustained release up to 24 h. Gelatin content influenced release kinetics by altering network density and hydrogel porosity. These findings underscore the importance of optimizing alginate-to-gelatin ratios and indicate that GSE-loaded hydrogels are promising candidates for controlled delivery of natural antioxidants in biomedical applications.