Cytoprotective Evaluation of Juglans regia L. Septum Extract and Development of Extract-Based Gels and Films for Topical Application

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Background/Objectives: Juglans regia L. septa are a rich source of phenolic compounds with potential skin-related biological activity. This study evaluated the cytoprotective activity of a lyophilised J. regia septum extract and developed extract-containing polymeric gels suitable for topical application and semi-solid extrusion (SSE) 3D printing. Methods: The extract was characterised by high-performance liquid chromatography with photodiode array detection (HPLC-PDA) and evaluated in H2O2-exposed human fibroblasts. Poly(vinyl alcohol) (PVA)-, sodium carboxymethyl cellulose (CMC)-, and hydroxyethyl cellulose (HEC)-based gels were prepared, and the selected formulation was processed into films by solvent casting and SSE 3D printing. The films were evaluated for thickness, moisture content, mechanical properties, and probe–film adhesiveness. Results: Ellagic acid was the predominant quantified phenolic compound (36.453 µg/mL). The free extract protected fibroblasts against H2O2-induced oxidative damage, with the greatest preservation of viable cells at 75 and 100 µg/mL. Increasing extract loading increased total quantified phenolic content in the gels from 10.95 to 27.98 µg/mL. The selected formulation was successfully processed into multilayer films. 3D-printed films showed numerically lower burst strength and breaking force per unit width than solvent-cast films, although pairwise differences were not significant. Hydration increased probe–film adhesiveness, while film moisture content decreased during 3 months of storage. Conclusions: These findings support the feasibility of incorporating cytoprotective J. regia extract into printable polymeric gels for topical film development.