Long-Acting and Safe Sunscreens with Ultrahigh Sun Protection Factor via Natural Lignin Encapsulation and Synergy
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Requirements for safe, stable, and long-acting sunscreens are successfully accomplished by natural lignin due to its broad-spectrum ultraviolet (UV)-blocking and synergistic properties. Chemical sunscreens are encapsulated in enzymatic hydrolysis lignin (EHL) by a one-step high-intensity ultrasound method. Chemical sunscreen/EHL microcapsules were formed with 3 min processing, and the product could be stored without leaking for more than a whole year. Adding H2O2 increased the cross-linking degree of EHL on the surface of the capsules. When 5 wt % alkyl polyglucoside (APG) was added as surfactant, the size of capsules dramatically decreased to ∼100 nm and the ratio of EHL and chemical sunscreen reached 1:1, which significantly enhanced UV-blocking ability of the composites. Compared to the creams containing chemical sunscreen/EHL microcapsules and free chemical sunscreen, the sun protection factor (SPF) of the cream containing the same amount of chemical sunscreen/EHL nanocapsules increased 85% and 195%, respectively. The cream containing 10 wt % of UVA and UVB type chemical sunscreen coencapsulated nanocapsules gave SPF 408. Due to antiphotolysis protection of EHL, the SPF of the creams increased initially and was maintained for more than 8 h under UV radiation. There was no obvious leaking or permeation of chemical sunscreens from the capsules. The EHL-based capsules showed good biocompatibility.