In the heat of summer, many people feel a need to slather on more sunscreen to prevent the sun's ultraviolet radiation from crisping their skin. But scientists may have found a new way to block these dangerous rays: melanin-imitating nanoparticles that protect skin cells from within. If proved, this approach could be used to develop better topical protection and possibly treatments for certain skin disorders as well.

The darkening pigment melanin is one of the body's primary natural defenses against UV-induced DNA damage. Below the skin's surface, special cells secrete melanosomes, which produce, store and transport melanin. These structures are absorbed by skin cells called keratinocytes and form protective, UV-blocking shells around the cells' nuclei. People suffering from diseases such as albinism and vitiligo, however, have faulty melanin production and are highly susceptible to the effects of UV.

To create synthetic versions of these melanosomes, researchers at the University of California, San Diego, bathed dopamine—a signaling chemical found in the brain and other parts of the body—in an alkaline solution. This step produced melaninlike nanoparticles with shells and cores made of polydopamine, a dopamine-based polymer. When incubated in a petri dish with human keratinocytes, the synthetic particles were absorbed by the skin cells and distributed around their nuclei like natural melanin.

The cells “are able to process [the synthetic nanoparticle] and then convert it into a sort of cap over the nucleus,” says study author Nathan Gianneschi, a biochemist now at Northwestern University. Like melanin, the synthetic material also functions as a pigment to darken skin, but “it wasn't that it just filled the cells and made them darker,” he says. “It actually structured them.”

Not only were the melaninlike nanoparticles transported and distributed throughout skin cells like natural melanin—they also protected the cells' DNA. The researchers incubated skin cells with nanoparticles and then exposed them to UV radiation for three days. Fifty percent of the skin cells that absorbed the nanoparticles survived, compared with just 10 percent of those without nanoparticles. The findings were published earlier this year in ACS Central Science.

Now that the team knows the melaninlike nanoparticles are treated the same as natural melanin and effectively protect cells, the next step will be determining the absorption mechanism.