Cellulose-Based Hydrogels Incorporating Olive Mill Wastewater (OMW): Preparation, Characterization, and In Vitro Antimicrobial Activity

Olive mill wastewater (OMW) is an agro-industrial byproduct rich in polyphenols and other bioactive compounds with documented antioxidant and antimicrobial properties. In this study, purified OMW fractions (RO1 and MD2), previously characterized by high polyphenol content and strong antioxidant activity, were incorporated (10% w/w) into cellulose-based hydrogels intended for topical application. Hydrogels were prepared using carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxypropyl methylcellulose (HPMC), and methylcellulose (MC) at concentrations of 1.5–2.0% (w/w). The formulations were characterized in terms of organoleptic properties, pH, rheological behavior, swelling capacity, weight loss, antioxidant activity (DPPH assay), and microbiological activity against selected skin pathogens, including antibiotic-resistant strains. Rheological analysis confirmed pseudoplastic behavior suitable for topical administration. OMW-loaded hydrogels exhibited significant radical scavenging activity compared to blank formulations and demonstrated antimicrobial efficacy, supporting the preservation of OMW bioactivity within the polymeric network. The results highlight the potential of cellulose-based hydrogels as sustainable and biocompatible carriers for the valorization of OMW in dermatological applications, particularly for the management of oxidative stress and bacterial skin infections.