Confocal Raman microscopy and multivariate statistical analysis for determination of different penetration abilities of caffeine and propylene glycol applied simultaneously in a mixture on porcine skin ex vivoстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 26 августа 2016 г.
Аннотация:a b s t r a c t
Propylene glycol is one of the known substances added in cosmetic formulations as a penetration enhancer.
Recently, nanocrystals have been employed also to increase the skin penetration of active components.
Caffeine is a component with many applications and its penetration into the epidermis is
controversially discussed in the literature. In the present study, the penetration ability of two components
– caffeine nanocrystals and propylene glycol, applied topically on porcine ear skin in the form of
a gel, was investigated ex vivo using two confocal Raman microscopes operated at different excitation
wavelengths (785 nm and 633 nm).
Several depth profiles were acquired in the fingerprint region and different spectral ranges, i.e.,
526–600 cm1 and 810–880 cm1 were chosen for independent analysis of caffeine and propylene glycol
penetration into the skin, respectively. Multivariate statistical methods such as principal component
analysis (PCA) and linear discriminant analysis (LDA) combined with Student’s t-test were employed
to calculate the maximum penetration depths of each substance (caffeine and propylene glycol). The
results show that propylene glycol penetrates significantly deeper than caffeine (20.7–22.0 lm versus
12.3–13.0 lm) without any penetration enhancement effect on caffeine. The results confirm that
different substances, even if applied onto the skin as a mixture, can penetrate differently.
The penetration depths of caffeine and propylene glycol obtained using two different confocal Raman
microscopes are comparable showing that both types of microscopes are well suited for such investigations
and that multivariate statistical PCA–LDA methods combined with Student’s t-test are very useful
for analyzing the penetration of different substances into the skin.