Penetration Depth of Propylene Glycol, Sodium Fluorescein and Nile Red into the Skin Using Non-Invasive Two-Photon Excited FLIM

Abstract

The stratum corneum (SC) forms a strong barrier against topical drug delivery. Therefore, understanding the penetration depth and pathways into the SC 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 (PG), sodium fluorescein (NaFl) and lipophilic Nile red (NR) into porcine ear skin ex vivo. Non-fluorescent PG was detected indirectly based on the pH-dependent increase in the fluorescence lifetime of SC components. The pH similarity between PG and viable epidermis limited the detection of PG. NaFl reached the viable epidermis, which was also proved by laser scanning microscopy. Tape stripping and confocal Raman micro-spectroscopy were performed additionally to study NaFl, which revealed penetration depths of ≈5 and ≈8 μm, respectively. Lastly, NR did not permeate the SC. 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.

Fluorescence-Coupled Techniques for Determining Rose Bengal in Dermatological Formulations and Their Application to Ex Vivo Skin Deposition Studies

“…To further evaluate the performance of the RB-loaded dermatological formulations, we investigated RB’s distribution within the dermatomed skin by multiphoton microscopy. Multiphoton microscopy, such as other fluorescence-based microscopical techniques, utilises the intrinsic fluorescence properties of some molecules in order to investigate the delivery of those molecules within the skin’s layers [ 49 ]. Herein, we present the micrographs of the skin samples at the end of 24 h of the permeation experiment ( Figure 8 ).…”

“…Fluorescence-coupled techniques have been widely used to evaluate the efficiency of drug delivery systems intended to be administered to the skin [ 49 ]; wide-field fluorescence and multiphoton microscopies are some of those techniques. Pena-Rodríguez and collaborators exploited the wide-field fluorescence microscopy to determine the biodistribution of Retinyl Palmitate-Loaded Transfersomes within the skin layers [ 49 ], aiming the epidermal delivery. Similarly, Mangion et al [ 50 ] employed multiphoton microscopy to assess the follicular delivery of zinc pyrithione.…”

Advanced Skin Antisepsis: Application of UVA-Cleavable Hydroxyethyl Starch Nanocapsules for Improved Eradication of Hair Follicle-Associated Microorganisms

“…Porcine ears without any visible injuries were selected for further examinations and the experiments were executed not later than 48 h after slaughter to exclude possible post-mortem skin changes [ 40 ]. The porcine ears were cleaned under cold tap water and dried with paper towels and stored at 4 °C until the experiments [ 41 ]. The porcine ears were fixed on a polystyrene board covered by aluminum foil by using cannulas.…”

Quantification of skin penetration of caffeine and propylene glycol applied topically in a mixture by tailored multivariate curve resolution‐alternating least squares of depth‐resolved Raman spectra

“…Noninvasive methods used for the quantitative/ qualitative determination of the penetration of CF and PG into the skin are limited to optical methods such as confocal Raman micro-spectroscopy (CRM) [29,30,[42][43][44][45], stimulated Raman scattering microscopy [46], twophoton tomography combined with fluorescence lifetime imaging [21,47], and laser scanning microscopy (labeling of the drug with a fluorescent dye is required) [48]. Invasive methods include the high-performance liquid chromatography analysis of SC tape strips [21,30] and of the skin interstitial fluid collected with microneedles [17].…”