(375a) Multilayer Core-Shell Nanocomposite Particles for Enhanced Uva/Uvb Protection in Sunscreens Via Atomic Layer Deposition

Recent developments in the medical field have attributed the onset of skin cancer to the long-term overexposure of UVA rays (320-400nm). Current commercial sunscreen products do not efficiently prevent the transmission of this portion of the UV spectrum; Sun Protection Factor (SPF) calculations are primarily correlated to the transmittance of UVB rays (290-320nm). Novel sunscreen materials are developed here using Atomic Layer Deposition (ALD) to create core-shell particles that can be easily dispersed in liquids while efficiently blocking both UVA and UVB rays. Composite titania/zinc oxide (TiO2/ZnO) particles capped with an alumina (Al2O3) nanolayer have been designed and synthesized for the benign protection from UVA/UVB ? rays. TiO2 scatters UVB-rays and ZnO absorbs UVA-rays very efficiently. The manufacture of these core-shell particles via novel ALD thin film technology allows for the synthesis of biosafe composite particles with dual effectiveness. In the first aspect of this work, two core-shell systems are evaluated with ALD coatings on commercial inorganic sunscreen ingredients. ZnO was deposited on nanosized TiO2 particles (25nm primary) and nanosized silica (SiO2) particles (40nm primary) to vary the n and k parameters of the core at UV wavelengths. Mie scattering theory has been applied to these colloidal dispersions consisting of coated particles smaller than the wavelength of light. In all instances, the composite particles are capped with an Al2O3 nanolayer to facilitate dispersion; rheological properties are addressed using an FDA approved sunscreen formulation. This Al2O3 nanolayer also prevents direct contact of the active TiO2/ZnO with the skin, thus protecting the skin from potential UV-photactivated reactions. Film thicknesses of both UV-active (ZnO) and UV-inactive (Al2O3 / SiO2) ALD layers have been tuned in accordance with multilayer core-shell theory to optimize the ability for these biosafe nanocomposite particles to prevent the onset of skin cancer. ALD functionality is used to enhance primary particles that are currently used in commercial cosmetic and sunscreen products.