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Au Naturale Nanoparticle Sun Protection
By: Katie Schaefer, C&T magazine
Posted: September 1, 2010, from the September 2010 issue of Cosmetics & Toiletries.
In 1876, Charles Darwin observed the secretion of yellow matter from the rootlets of ivy. Little was known about the material until 2008, when Mingjun Zhang, PhD, an associate professor of biomedical engineering at the University of Tennessee, and his research team found nanoparticles in the yellow matter.
Zhang’s described his first findings as being focused on the climbing mechanisms of English ivy (Hedera helix) and Boston ivy (Parthenocissus tricuspidata). “I was trying to understand the strong force ivy generates to attach to structures,” noted Zhang, whose team analyzed the secretions with atomic force microscopy (AFM). “These nanoparticles are secreted by the ivy to fill holes and dents in the material that it attaches to, which generates crosslinking with the surface to increase adhesion forces.”
A year and a half later, Zhang attended a nanobiotechnology conference in San Francisco, where a speaker discussed toxicity concerns over metal-based nanoparticles used as UV filters. Since Zhang had access to the English ivy nanoparticles, he and his team tested them and found they could absorb and scatter UV light.
TiO2 and ZnO vs. English Ivy
Due to their white appearance on skin, titanium dioxide (TiO2) and zinc oxide (ZnO) often are reduced to nano sizes to offer more transparent yet equal UV protection. Many nanoparticles, according to Zhang, have the ability to absorb and scatter UV radiation due to their large surface-to-volume ratio; however, he finds that English ivy nanoparticles may offer better sun protection than metal-based nanoparticle UV filters with improved optical properties, less safety concern and a more uniform particle size.
Zhang and his team compared the optical extinction spectra of English ivy nanoparticles against that of TiO2. At 4.92 μg/mL, the English ivy nanoparticles exhibited significant extinction in the UV region (280–400 nm) but decreased after that, suggesting the English ivy nanoparticles would be effective at protecting skin. The results also indicated that English ivy nanoparticles have high transmittance in the visible UV region, which makes them “invisible,” according to Zhang. At the same concentration, TiO2 exhibited a lower extinction level in the UV region (250–350 nm) and decreased slowly after the UV region.