Nanoparticles as delivery vehicles for sunscreen agents

Sunscreen filters, which block hazardous UV radiation, are commonly applied in cosmetic products to protect the skin, the hair, or the product itself. Most sunscreen formulations are emulsions or creams. However, formulations based on nanoparticles as the delivery vehicle for the sunscreen compounds potentially have advantages in terms of retention on the skin, lack of penetration across the epidermal layer and UV attenuation by both absorption and scattering. In this study, sunscreen nanoparticle suspensions are prepared via the novel Flash NanoPrecipitation process (FNP), which involves rapid micromixing followed by block copolymer directed assembly of nanoparticles. The block copolymer stabilizer is polystyrene-block-polyethylene glycol (PS-b-PEG) with a homopolymer polystyrene (PS) as the co-solute in the nanoparticle core. By changing the filter and/or PS concentration, stable nanoparticles with sizes from 80 to 200 nm are prepared. Most importantly, FNP enables incorporation of both organic and inorganic hydrophobic filters into nanoparticles, and thus offers broad-spectrum sun protection. The nanocolloids offer enhanced UV protection because they attenuate light by both adsorption and scattering. Three organic filters, ethylhexyl triazone (Uvinul T 150), benzophenone-3 (Uvinul M 40), and diethylamino hydroxybenzoyl hexyl benzoate (Uvinul A Plus) and two nano-sized inorganic filters, zinc oxide and titanium dioxide are examined. In addition it is found the polystyrene core material offers significant UV blocking in the UVC range of 200–280 nm. Dynamic light scattering (DLS) reveals that the nanoparticles’ size distribution is narrow and remains stable (over 80 days). The combination of organic and inorganic filters enables tunable UV protection over the wavelength range 280–400 nm. In conclusion, flash nanoprecipitation provides a new formulation method of encapsulating hydrophobic organic and inorganic sunscreen filters.