Tracking heavy‐water‐incorporated confocal Raman spectroscopy for evaluating the effects of PEGylated emulsifiers on skin barrier

Abstract

The class of PEGylated emulsifiers finds broad application in the pharmaceutical and cosmetic industry. We target on one of the categories of polyethylene glycol (PEG) alkyl ethers with different lipophilic and hydrophilic chain length and aim to examine their effects on the skin comprehensively. In this study, we employed confocal Raman spectroscopy for skin depth profiling and imaging. A unique probe of heavy water (D 2 O) was incorporated, which can be tracked percutaneously and simultaneously monitor the effects caused by emulsifiers. According to the results, most of the PEGylated emulsifiers caused changes in skin lipid content/organization and induced the alteration in relative water content/hydrogen bonding structure. The results obtained from the depth profiling analysis provided the possibility to estimate the least penetration depth of emulsifiers. Among them, PEG-20 ethers displayed the most penetration ability. Meanwhile, it is interesting to find that the treatment of emulsifiers also affected the spatial distribution of D 2 O whose differences were in line with the molecular skin variations. In particular, the isotopic H/D substitution in the skin was highlighted in detail. This result supports the possibility to use D 2 O as an excellent and costeffective probe to evaluate the skin barrier function.

Current Views on Noninvasive in vivo Determination of Physiological Parameters of the Stratum Corneum Using Confocal Raman Microspectroscopy

“…Additionally to the composition, the noninvasive evaluation of the influence of topically applied cosmetic or medical formulations on the parameters of the SC is up to date and was previously only realized ex vivo using Raman spectroscopy [73][74][75]. The development of the above described algorithms allows the investigations of the influence of topically applied cosmetic or medical formulations on the components and physiological parameters of the human SC in vivo and noninvasively using confocal Raman microspectroscopy [76][77][78][79], which is in great demand for cosmetic and pharmaceutical industries.…”

Novel aspects of Raman spectroscopy in skin research

“…An increased content of unbound water within the SC, however, was associated with disordered lipid and protein states. Recently, the application of heavy water was investigated by CRS 89 ; different ethoxylated emulsifiers were dissolved in D 2 O to probe their effect on skin biochemistry while avoiding additional effects on the OH bond of the skin spectrum through externally applied water. The D 2 O distribution within the skin was well discernible due to its OD stretching band and was clearly affected by the co‐applied selected ethoxylated emulsifiers in dependence of their chemical structure and the positive control sodium laureth sulphate (SLES).…”

Research Progress in the Medical Application of Heavy Water, Especially in the Field of D2O-Raman Spectroscopy

“…The combination of heavy water and Raman microscopy can sensitively identify small changes in the molecular composition of skin and can detect skin at different depths. Heavy water, as a skin probe, can be used to detect skin water-related properties by extracting spectra from each pixel depth and distinguishing endogenous and exogenous hydrogen bonds 62 - 63 . By using different hydrogen-bonding water types to calculate the relative water content, the total water content of different skin depths can be calculated 64 .…”