Formulation and in Vitro Sun Protection Evaluation of Gel Prepared from Brown Algae <i>Sargassum oligocystum</i> Extract

Abstract

Background: Growing awareness of ultraviolet (UV)-induced skin damage has increased the demand for effective sunscreen formulations. However, concerns regarding the safety and environmental impact of synthetic UV filters have driven the exploration of natural alternatives. Marine algae, particularly brown algae, represent a promising source of bioactive compounds with photoprotective properties. Objectives: This study aimed to formulate and evaluate topical gel formulations containing Sargassum oligocystum extract and to investigate their potential as natural UV-protective agents. Methods: Eight gel formulations were prepared using two gelling agents, carbomer and hydroxypropyl methylcellulose (HPMC), with varying concentrations of S. oligocystum extract (0%, 5%, 7%, and 10%). The extract was evaluated for total phenolic content using the Folin-Ciocalteu method. The formulated gels were assessed for physicochemical properties, including appearance, pH, viscosity, and spreadability. In vitro UVB-absorbing activity was determined using UV-Vis spectrophotometry and the Mansur equation. Results: The total phenolic content of S. oligocystum extract was 30.611 mg gallic acid equivalents (GAE)/g extract. After exclusion of the biphasic F4 formulation, the remaining formulations were physically stable over 3 months of storage, with no significant changes in appearance or pH. The pH of the carbomer-based gels ranged from 6.75 to 7.15, whereas that of the HPMC-based gels ranged from 5.91 to 6.49. Gel spreadability under a 250 g weight ranged from 6.111 to 8.334 g·cm/s. At 10 rpm, the measurable carbomer gels had viscosities of 40,831 to 54,888 cP, whereas the HPMC gels had viscosities of approximately 6,500 to 8,400 cP. The lowest in vitro spectrophotometric sun protection factor (SPF) estimates (approximately 0.7 to 1) were observed in formulations without Sargassum extract (F1 and F5). Formulations containing the extract had significantly higher in vitro SPF values, ranging from 5.3 to 8.8, indicating measurable UV-protective activity; however, these values remained within the low-protection range. Conclusions: S. oligocystum extract significantly increased the in vitro spectrophotometric SPF estimates of the gels. SPF increased significantly with increasing extract concentrations up to 7%, whereas increasing the concentration to 10% produced no statistically significant additional increase, indicating a plateau in the UV-protective effect. The extract shows potential as a natural UV-protective agent; however, further optimization is required to achieve SPF levels suitable for commercial sunscreen application.