Physicochemical Properties of Freeze–Dried Bigel-Based Materials Composed of Sodium Alginate/Whey Protein Isolate Hydrogel and Ethylcellulose/Sunflower Oil Oleogel

Freeze-drying bigels is a novel technique for developing functional materials for dermatological and cosmetic use, leveraging the benefits of two structured phases. This study optimized freeze-dried bigels composed of whey protein isolate (WPI)/sodium alginate/glycerin hydrogel and ethylcellulose (EC)/Span 80/sunflower oil oleogel at varying hydrogel/oleogel ratios. The materials showed swelling ratios from 50% to 255%, with higher values for a lower oleogel content and higher polymer concentration. The higher oleogel content extended the degradation from a few hours to 7 days. The polymer concentrations and hydrogel/oleogel ratios influenced Young's modulus (1.25-3.7 MPa). Porosity varied from 35% to 58%, and density varied from 100 to 200 mg/mL. The residual moisture content (5% to 20%) increased with EC content and decreased with WPI and oleogel content. These findings underscore the role of polymer concentrations and phase ratios in tuning the physicochemical properties of freeze-dried gels, positioning them as promising biomaterials for skincare and cosmetic applications.