Current commercial sunscreens use compounds to filter out damaging ultraviolet (UV) light, but these agents can have adverse effects as they penetrate past the surface skin into the bloodstream.
The agents have been found in human breast tissue and urine and are known to disrupt the normal function of some hormones.
Also, the exposure of the UV filters to light can produce toxic reactive oxygen species that can damage cells, tissues and DNA, potentially causing cancerous tumors.
A team of bioengineers and dermatologists at Yale University in New Haven, CT, set out to address these hazards by combining nanoparticle-based drug delivery and the molecular and cellular characteristics of the skin.
Their solution was to capture the UV-blocking compounds in bioadhesive nanoparticles (BNPs) that adhere well to the skin but do not penetrate beyond the surface.
Bioadhesive nanotechnology provides safer delivery method
A commonly used sunscreen padimate O (PO), which is related to the better-known sunscreen PABA, was encapsulated inside a nanoparticle, a minute molecule often used to transport drugs and other agents into the body.
The BNP containing PO was tested on pigs for penetration into the skin. A control group of pigs received the PO alone, not encapsulated in a nanoparticle.
Although BNPs are larger than skin pores and, therefore, unlikely to pass through, it was thought that they could still pass through the larger hair follicles, beyond the surface layers of skin, through blood vessels in the deeper layers and into the bloodstream.
However, not only did the PO inside the nanoparticle remain on the skin’s surface, but the BNPs remained outside the hair follicle openings, prevented, apparently, by their adhesive properties that caused them to stick to the skin’s surface.
Further tests showed the BNPs to be water resistant, remaining on the skin for a day or more, yet easily removed by towel wiping. They also disappeared within days through natural exfoliation of the surface skin.
UV protection retained, potentially enhanced
The next step was to see if the BNP-encapsulated sunscreen retained its UV-filtering properties when encapsulated in the BNPs.
The BNP formulation provided UV protection as effectively as the commercial products when applied directly to the skin of a hairless mouse, even though the BNPs carried only 5% of the amount of commercial sunblock.
Finally, the researchers tested the encapsulated sunscreen for the formation of damaging oxygen-carrying molecules known as reactive oxygen species (ROS) when exposed to UV light.
They hypothesized that any ROS created by the sunscreen’s interaction with UV would remain inside the BNP, unable to damage surrounding tissue.
Following exposure to UV light, no damaging ROS were detected outside the nanoparticle, indicating that any harmful agents that formed stayed inside the nanoparticle, unable to make contact with the skin.
Jessica Tucker, PhD, director of the National Institute of Biomedical Imaging and Bioengineering (NIBIB) Program in Delivery Systems and Devices for Drugs and Biologics, says the work uses a novel bioengineering idea to approach a significant health problem.
Senior author Mark Saltzman, PhD, of the Yale School of Engineering and Applied Science, believes the new formulation combines “the best properties of an effective sunscreen with a safety profile that alleviates the potential toxicities of the actual sunscreen product because it is encapsulated and literally never touches the skin.”
Co-senior author Dr. Michael Girardi says the team is now “in a position to assess the effects on human skin.”