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NATURALLY-occurring nanoparticles found in common ivy, Hedera helix, are an effective sunscreen, according to new research.

A team at the University of Tennessee, Knoxville, US, led by biomedical engineering professor Mingjun Zhang, were examining the properties of nanoparticles produced in ivy roots which improve the roots’ adhesiveness to the surfaces they cling to, when they found that as well as adhesive qualities, the nanoparticles absorbed and scattered light, which is how sunscreens work. Standard sunscreens contain metal oxide nanoparticles for this purpose, usually titanium or zinc oxide, but concerns have been raised about their potential toxicity with long-term use.

"Ivy nanoparticles are more uniform than the metal-based nanoparticles, and have unique material properties, which may help to enhance the absorption and scattering of light, and serve better as a sun-blocker," says Zhang.

Zhang and his colleagues evaluated the natural nanoparticles on four criteria – the ability to absorb and scatter ultraviolet light, toxicity to mammalian cells, biodegradability, and the potential for diffusion through skin. Ivy nanoparticles were tested using a spectrophotometric assay for sunscreen potential and found to be four times as effective as titanium dioxide at absorbing and scattering ultraviolet light. Toxicity was tested using the HeLa human cell line with ivy nanoparticles compared to titanium dioxide. At concentrations of 1 µg/ml, the ivy nanoparticles caused no cell death, while the same concentration of titanium dioxide nanoparticles did. The ivy nanoparticles were found to be broken down by standard cell enzymes and a mathematical model showed that in a standard 8 hour exposure period for sunscreens, the nanoparticles would not penetrate more than 8 µm into the skin.

The adhesive qualities of the nanoparticles would also be useful for sunscreen, allowing then to remain on the skin for longer during activities such as swimming, for example.

"In general, it is not a good idea to have more metal-based nanoparticles for cosmetic applications. They are a significant concern for the environment. Naturally occurring nanoparticles originated from plants seem to be a better choice, especially since they have been demonstrated to be less toxic and easily biodegradable," says Zhang.

Journal of Nanobiotechnology doi: 10.1186/1477-3155-8-12