Just as an examination of the burrs of seeds that kept sticking to his clothes led Swiss engineer, George de Mestral, to develop Velcro, a search for an explanation as to why the ivy in his backyard clung to this fence so tightly has led Mingjun Zhnag to a new discovery. It seems that tiny particles secreted from ivy rootlets could have applications for military technologies, medical adhesives, drug delivery and, most recently, sun-block that could protect skin from UV radiation at least four times better than the metal-based sunblocks found on store shelves today.
Zhang, an associate professor of biomedical engineering at the University of Tennessee, Knoxville, speculated the greenery's hidden power lay within a yellowish material secreted by the ivy for surface climbing. He placed this material onto a silicon wafer and examined it under an atomic force microscope and was surprised by what it revealed – lots of nanoparticles. The properties of these tiny bits create the ability for the vine leaves to hold almost two million more times than its weight. It also has the ability to soak up and disperse light, which is integral to sunscreens.
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“Nanoparticles exhibit unique physical and chemical properties due to large surface-to-volume ratio which allows them to absorb and scatter light," Zhang said. "Titanium dioxide and zinc oxide are currently used for sunscreen for the same reason, but the 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."
The team's study indicates that ivy nanoparticles can improve the extinction of ultraviolet light at least four times better than its metal counterparts. Furthermore, there is evidence that titanium dioxide nanoparticles used in sunscreens causes genetic damage in mice and also has a negative effect on beneficial bacteria in the environment. Zhang notes some studies have shown that the small-scale metal oxides in sunscreen can wind up in organs such as the liver or brain.
Ivy nanoparticles, on the other hand, exhibit better biocompatibility with humans and the environment. The team's studies indicate that the ivy nanoparticles were less toxic to mammalian cells, have a limited potential to penetrate through human skin, and are easily biodegradable.
"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," Zhang said.
Sunscreens made with ivy nanoparticles may not need to be reapplied after swimming. That's because the plant's nanoparticles are a bit more adhesive so sunscreens made with them may not wash off as easily as traditional sunscreens. And while sunscreens made with metal-based nanoparticles give the skin a white tinge, sunscreens made with ivy nanoparticles are virtually invisible when applied to the skin.