Oleogel Dressings for Skin Therapy: Physicochemical and Bioactive Properties of Cosmetic Oil-Based Systems Enriched with Essential Oils

Developing potential skincare formulations capable of simultaneously managing infection and promoting tissue repair remains a critical challenge in dermatological care. This study engineered bioactive oleogels using sunflower wax (SFW), rice bran wax (RBW), and 12-hydroxystearic acid (HSA) to deliver a synergistic essential oil blend (ginger, cinnamon, tea tree, geranium). A D-optimal mixture design optimized formulations to match the textural profile of a commercial benchmark. Crucially, the fatty acid architecture of the carrier oil emerged as a primary determinant of network integrity; the high oleic acid content in camellia oil facilitated robust RBW crystallization by minimizing steric hindrance, whereas the polyunsaturated, kinked structure of linoleic acid in almond oil disrupted SFW networks, resulting in lower stiffness. Thermal characterization (DSC) established a distinct stability hierarchy with RBW exhibiting the highest melting point (Tp = 60.1 °C) and enthalpy (ΔHm = 7.79 ± 0.74 J/g). Thermogravimetric analysis (TGA) confirmed high thermal resistance for wax-based systems (Tdeg ≈ 357 °C), whereas HSA displayed a biphasic degradation starting at ~206 °C. FTIR spectroscopy verified the stable physical entrapment of bioactives, with the lipid vehicle dominating the spectral fingerprint. Rheological profiling revealed that RBW oleogels, structured in high-oleic camellia oil, formed rigid networks (G' ≈ 5.7 × 104 Pa) with high yield stress (20.91 Pa), offering superior retention. In contrast, HSA oleogels displayed "smart" thixotropic recovery with lower stiffness (G' ≈ 2.1 × 104 Pa) and a distinct melting peak at 22.5 °C, compared to 60.1 °C for RBW. All formulations achieved a >2 Log₁₀ reduction (99%) in <i>Staphylococcus aureus</i> and <i>Pseudomonas aeruginosa</i> viability after 12 h. Furthermore, in vitro keratinocyte assays identified a hormetic therapeutic window at 1-5 μg/mL (essential oil blend equivalent); specifically, SFW oleogels at 5 μg/mL stimulated proliferation to 158.07% relative to controls. These findings confirm that optimizing the lipid vehicle-bioactive interface creates dual-action scaffolds capable of simultaneously managing infection and stimulating in vitro keratinocyte proliferation.