Development and Characterization of Carrageenan-Based Hydrogels Enriched with Calendula officinalis Extract for Topical Skin Applications

Carrageenan-based hydrogels are promising matrices for topical cosmetic applications because their highly hydrated polymer networks can be modified to incorporate bioactive compounds and adjust functional properties. In this study, Calendula officinalis flower extracts were incorporated into κ-carrageenan-based hydrogels either directly or after loading into chemically crosslinked gelatin microspheres. The obtained formulations were characterized in terms of morphology, compressive modulus, swelling behaviour, thermal stability, and selected biophysical skin parameters. The hydrogels showed formulation-dependent differences in surface morphology, mechanical properties, water uptake, and thermal behaviour. The compressive modulus ranged from 14.10 ± 1.15 to 23.20 ± 1.46 kPa, with the highest value observed for the hydrogel containing directly incorporated hydroglycolic extract. This formulation also exhibited the lowest degree of swelling, whereas higher swelling was generally observed in microsphere-containing systems. All formulations showed three main stages of thermal mass loss. Preliminary skin measurements showed no pronounced persistent increase in transepidermal water loss or marked changes in the A* parameter following hydrogel application. The results show that direct and microsphere-mediated incorporation represent distinct formulation strategies resulting in different physicochemical properties of carrageenan-based hydrogels. Preliminary skin measurements additionally provided initial information on their short-term response following topical application.