Nano Sunscreen from the Garden

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, reported Katie Schaefer in Cosmetics & Toiletries magazine’s September 2010 article “Au Naturale Nanoparticle Sun Protection.”

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. “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 about 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.

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 English ivy nanoparticles against that of titanium dioxide, a common used sun screen ingredient that appears white on skin. The results indicated that English ivy nanoparticles have high transmittance in the visible UV region, which makes them “invisible,” according to Zhang.

The ability of English ivy nanoparticles to protect skin from UV also is enhanced by their size and smoothness. “We observed that the [English ivy nanoparticles] are uniform at [within a specific size range], and they have a smooth surface. This smoothness will enhance absorption or scattering of light,” said Zhang.

Although it was important for Zhang to assess the UV protection of the English ivy nanoparticles, it was equally as important to assess their skin penetration and toxicity for comparison with metal-based nanoparticle UV filters. It was concluded that English ivy nanoparticles could not penetrate the stratum corneum layer of skin in cosmetic applications.

Additionally, the adhesion properties of the ivy nanoparticles could enhance the durability of sunscreens, reducing the frequency of re-application. Zhang’s team is still refining ways to optimize the nanoparticles for specific applications, as well as an eco-friendly scale-up method.

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