UV filter entrapment in mesoporous silica hydrogel for skin protection against UVA with minimization of percutaneous absorption

The UVA absorbers such as avobenzone are widely used for sunlight protection; however, they show a significant skin penetration. The aim of the present study was to formulate UVA absorbers into mesoporous silicas (MSs) for enhanced UVA protection with reduced percutaneous absorption. Two MSs prepared with different structure-directing agents (Pluronic P123 as single MS and combined Pluronic P123-Pluronic F68 as hybrid MS) were synthesized in this study. The hybrid MS exhibited higher specific surface area (853 m²/g) than the single MS (764 m²/g). The particle sizes of single MS and hybrid MS were about 1 and 1.5 μm, respectively. The adsorbed avobenzone had greatly decreased crystallinity compared with free avobenzone. The in vitro photoprotection determined by UVA/UVB ratio showed that the MS-loaded avobenzone in hydrogel endowed a synergistic effect on UVA protection compared to the free avobenzone. The skin absorption test using Franz diffusion cell indicated that the skin permeation of avobenzone and oxybenzone from MSs in semisolid preparations was one-third to one-half of those from free control. This effect was observed by using both pig skin and UVA-damaged nude mouse skin as the penetration barriers. Topical application of hybrid MS on nude mouse skin before UVA irradiation had prevented the increased transepidermal water loss (TEWL), furrow formation, keratinocyte apoptosis, and neutrophil infiltration. Our findings conclude that MSs containing avobenzone or oxybenzone effectively ameliorated UVA-induced skin disruption and reduced the possible toxicity elicited by percutaneous penetration.