Imaging technique shows nanoparticles do not penetrate skin

Oct. 1, 2012
Research by scientists at Bath University (Bath, UK) is challenging claims that nanoparticles in cosmetic creams are able to deliver active ingredients deep inside the skin.

Research by scientists at Bath University (Bath, UK) is challenging claims that nanoparticles in medicated and cosmetic creams are able to transport and deliver active ingredients deep inside the skin.

The Bath study discovered that even the smallest of nanoparticles did not penetrate the skin’s surface.

The findings have implications for pharmaceutical researchers and cosmetic companies that design skin creams with nanoparticles that are supposed to transport ingredients to the deeper layers of the skin. However, the findings will also allay safety concerns that potentially harmful nanoparticles such as those used in sunscreens can be absorbed into the body.

The scientists used a technique called laser scanning confocal microscopy to examine whether fluorescently-tagged polystyrene beads, ranging in size from 20 to 200nm, were absorbed into the skin.

The key feature of confocal microscopy is its ability to acquire in-focus images from selected depths, a process known as optical sectioning. Images are acquired point-by-point and reconstructed with a computer, allowing three-dimensional reconstructions of topologically complex objects.

Using the technique, the researchers found that even when the skin sample had been partially compromised by stripping the outer layers with adhesive tape, the nanoparticles did not penetrate the skin’s outer layer, known as the stratum corneum.

"Using confocal microscopy has allowed us to unambiguously visualize and objectively assess what happens to nanoparticles on an uneven skin surface. Whereas earlier work has suggested that nanoparticles appear to penetrate the skin, our results indicate that they may in fact have simply been deposited into a deep crease within the skin sample," says Professor Richard Guy from the university’s department of pharmacy and pharmacology.

"The skin’s role is to act as a barrier to potentially dangerous chemicals and to reduce water loss from the body. Our study shows that it is doing a good job of this. So, while an unsuspecting consumer may draw the conclusion that nanoparticles in their skin creams, are ‘carrying’ an active ingredient deep into the skin, our research shows this is patently not the case," he added.

The microscopy image above shows the nanoparticles in green on the skin's surface.

The results of the work were published in the Journal of Controlled Release. Details can be found here.

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-- Dave Wilson, Senior Editor, Vision Systems Design

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