Penetration Depth of Propylene Glycol, Sodium Fluorescein and Nile Red into the Skin Using Non-Invasive Two-Photon Excited FLIM
The stratum corneum (<i>SC</i>) forms a strong barrier against topical drug delivery. Therefore, understanding the penetration depth and pathways into the <i>SC</i> is important for the efficiency of drug delivery and cosmetic safety. In this study, TPT-FLIM (two-photon tomog...
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Main Authors: | , , , , , , , |
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Format: | Book |
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MDPI AG,
2022-08-01T00:00:00Z.
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Summary: | The stratum corneum (<i>SC</i>) forms a strong barrier against topical drug delivery. Therefore, understanding the penetration depth and pathways into the <i>SC</i> is important for the efficiency of drug delivery and cosmetic safety. In this study, TPT-FLIM (two-photon tomography combined with fluorescence lifetime imaging) was applied as a non-invasive optical method for the visualization of skin structure and components to study penetration depths of exemplary substances, like hydrophilic propylene glycol (<i>PG</i>), sodium fluorescein (<i>NaFl</i>) and lipophilic Nile red (<i>NR</i>) into porcine ear skin ex vivo. Non-fluorescent <i>PG</i> was detected indirectly based on the pH-dependent increase in the fluorescence lifetime of <i>SC</i> components. The pH similarity between <i>PG</i> and viable epidermis limited the detection of <i>PG</i>. <i>NaFl</i> reached the viable epidermis, which was also proved by laser scanning microscopy. Tape stripping and confocal Raman micro-spectroscopy were performed additionally to study <i>NaFl</i>, which revealed penetration depths of ≈5 and ≈8 μm, respectively. Lastly, <i>NR</i> did not permeate the <i>SC</i>. We concluded that the amplitude-weighted mean fluorescence lifetime is the most appropriate FLIM parameter to build up penetration profiles. This work is anticipated to provide a non-invasive TPT-FLIM method for studying the penetration of topically applied drugs and cosmetics into the skin. |
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Item Description: | 10.3390/pharmaceutics14091790 1999-4923 |