Microencapsulated UV filter@ZIF-8 based sunscreens for broad spectrum UV protection†
Sunscreens play a vital role in protecting human skin from photodamage upon UV exposure, but their effectiveness is limited by degradation and phototoxicity. Photoactivation of UV filters in sunscreen can generate reactive oxygen species, with accompanying cytotoxicity. Herein, we report stable, safe, fluorescent, and long-lasting sunscreens produced by microencapsulation of organic UV filters octylmethoxycinnamate (OMC) and butyl-methoxydibenzoylmethane (BMDM), alone and together, into a microporous zeolitic imidazole framework (ZIF-8). The visibly transparent OMC + BMDM@ZIF-8 sunscreens displayed complete broad-spectrum photoprotection against UV light even after 24 hours. Photostability testing of the sunscreens demonstrated the photo-protective nature of microporous ZIF-8 for stabilizing these UV filters. The sun protection factor (SPF) values for lotions containing 10% (w/w) OMC@ZIF-8, BMDM@ZIF-8 and OMC + BMDM@ZIF-8 sunscreens decreased from 29.8 to 26.0, 32.5 to 26.4, and 62.1 to 53.0, respectively, upon 24 hours of intense UV exposure. No release of the UV filters from the encapsulated formulations was observed. The ZIF-8 particles are too large to be transported across the stratum corneum. Thus, our findings suggest that zeolitic framework-encapsulated sunscreens could provide prolonged UV-protection efficacy and ultra-high SPF with reduced potential for degradation, phototoxicity, and transport across the skin.