Image of the distribution profile of targets in skin by Raman spectroscopy-based multivariate analysis

Improvement of lidocaine skin permeation by using passive and active enhancer methods

Lidocaine is generally recognized and preferred for local anaesthesia, but in addition, studies have described additional benefits of lidocaine in cancer therapy, inflammation reduction, and wound healing. These properties contribute to its increasing importance in dermatological applications, and not only in pain relief but also in other potential therapeutic outcomes. Therefore, the purpose of our study was to enhance lidocaine delivery through the skin. A stable nanostructured lipid carrier (NLC), as a passive permeation enhancer, was developed using a 23 full factorial design. The nanosystems were characterized by crystallinity behaviour, particle size, zeta potential, encapsulation efficiency measurements, and one of them was selected for further investigation. Then, NLC gel was formulated for dermal application and compared to a traditional dermal ointment in terms of physicochemical (rheological behaviour) and biopharmaceutical (qualitative Franz diffusion and quantitative Raman investigations) properties. The study also examined the use of 3D printed solid microneedles as active permeation enhancers for these systems, offering a minimally invasive approach to enhance transdermal drug delivery. By actively facilitating drug permeation through the skin, microneedles can complement the passive transport achieved by NLCs, thereby providing an innovative and synergistic approach to improving lidocaine delivery.

Optical Methods for Non-Invasive Determination of Skin Penetration: Current Trends, Advances, Possibilities, Prospects, and Translation into In Vivo Human Studies

Information on the penetration depth, pathways, metabolization, storage of vehicles, active pharmaceutical ingredients (APIs), and functional cosmetic ingredients (FCIs) of topically applied formulations or contaminants (substances) in skin is of great importance for understanding their interaction with skin targets, treatment efficacy, and risk assessment-a challenging task in dermatology, cosmetology, and pharmacy. Non-invasive methods for the qualitative and quantitative visualization of substances in skin in vivo are favored and limited to optical imaging and spectroscopic methods such as fluorescence/reflectance confocal laser scanning microscopy (CLSM); two-photon tomography (2PT) combined with autofluorescence (2PT-AF), fluorescence lifetime imaging (2PT-FLIM), second-harmonic generation (SHG), coherent anti-Stokes Raman scattering (CARS), and reflectance confocal microscopy (2PT-RCM); three-photon tomography (3PT); confocal Raman micro-spectroscopy (CRM); surface-enhanced Raman scattering (SERS) micro-spectroscopy; stimulated Raman scattering (SRS) microscopy; and optical coherence tomography (OCT). This review summarizes the state of the art in the use of the CLSM, 2PT, 3PT, CRM, SERS, SRS, and OCT optical methods to study skin penetration in vivo non-invasively (302 references). The advantages, limitations, possibilities, and prospects of the reviewed optical methods are comprehensively discussed. The ex vivo studies discussed are potentially translatable into in vivo measurements. The requirements for the optical properties of substances to determine their penetration into skin by certain methods are highlighted.

Quantitative determination of concentration profiles of skin components and topically applied oils by tailored multivariate curve resolution-alternating least squares using in vivo confocal Raman micro-spectroscopy

The main components of the stratum corneum (SC), water, lipids, and proteins, are non-homogeneously distributed throughout the depth. The quantitative determination of their concentration profiles and penetration depth of topically applied substances are urgent topics of dermatological and cosmetic research. Confocal Raman micro-spectroscopy has distinct advantages when determining semi-quantitative concentrations of SC components and topically applied substances non-invasively and in vivo. In this work, we applied a tailored multivariate curve resolution-alternating least squares (tMCR-ALS) method to analyze Raman spectra of the SC in the 2000-4000 cm-1 region for quantitatively determining the concentrations of water, lipids, proteins, and topically applied oils using substance-related spectral loadings which were allowed to change depth-dependently from the SC's surface toward its bottom. tMCR-ALS makes matching of depth-dependent signal attenuation, that is, the normalization on keratin, unnecessary and requires only a few additional experiments for calibration - Raman spectra of the pure materials and their densities.