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The hydration capacities of a biomimetic polymer, 2-methacryloyloxethylphosphorylcholine polymer (pMPC), alone and microencapsulated, in association with another well known hydrating polymer, Hyaluronic acid, were investigated in vitro on skin models and in vivo on volunteers by using confocal Raman microspectroscopy. The hydration impact and the relative water content in the Stratum corneum were calculated from the Raman spectra using the OH (water)/CH3 (protein) ratio. Moreover, the follow-up of the presence of pMPC through the Stratum corneum was possible with confocal Raman microspectroscopy, using a characteristic vibration of pMPC, different from that of the encapsulating material. From our in vitro measurements, the improved hydration of the Stratum corneum was confirmed by the use of the encapsulated form of pMPC, which was higher when combined with Hyaluronic acid. On the basis of these in vitro findings, we validated this trend in in vivo measurements on 26 volunteers, and found a good correlation with the in vitro results. Mechanical and ultrastructural studies have been carried out to demonstrate the positive effects of the pMPC on the Stratum corneum function, namely the interaction with lamellar lipids and the plasticizing effects, which are both supposed to spell out the moisturizing effect. This study demonstrates the efficiency of a original hydrating agent, pMPC, entrapped with Hyaluronic acid in a new type of microcapsules by the use of a novel tool developed for both in vitro and in vivo approaches. This indicates a new step to evaluate and improve new moisturizers in response to the cosmetics or dermatologic demands.

The use of human skin models for performing cutaneous bioavailability studies has been little investigated. For instance, only few studies have been reported on human skin models dealing with vehicle effects on percutaneous penetration. The present study aimed at evaluating the influence on caffeine’s and α-tocopherol’s cutaneous bioavailability of cosmetic vehicles such as a water-in-oil emulsion, an oil-in-water emulsion, a liposome dispersion and a hydrogel applied at finite dose using the reconstructed human skin models EpiDerm^® and Episkin^®. The results were compared with those obtained in human skin ex vivo using similar experimental conditions. It was demonstrated that the rank order of solute permeability could be correctly predicted when the preparation was applied at a finite dose in human skin models, at least when solutes with far different physicochemical properties such as caffeine and α-tocopherol were used. If only slight effects of cosmetic vehicle on skin bioavailability were observed in human skin ex vivo, they were less predictable using skin models. Especially, alcohol-containing vehicles seemed to behave differently in EpiDerm as well as in Episkin than on human skin ex vivo. Stratum corneum intercellular lipid composition and organization of human skin models differ to some extent from that of human stratum corneum ex vivo, which contributes to less pronounced barrier properties, together with the increased hydration of the outermost stratum corneum layers of the models. These features, as well as still unknown factors, may explain the differences observed in vehicle effects in human skin ex vivo versus human skin models.

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ObjectiveRetinol (Vitamin A) is one of the most effective molecules for the treatment of skin aging. However, it degrades rapidly under the influence of light, oxygen, metal ions, and oxidizing agents. To prevent this, stabilizing systems are used commonly. Notably, butylated hydroxytoluene (2,6‐di‐tert‐butyl‐p‐cresol) (BHT) and ethylenediaminetetraacetic acid (EDTA) salts exhibit excellent antioxidant and metal‐chelating properties but are not eco‐friendly. In this study, our goal was to develop a new eco‐friendly stabilization system for retinol‐based formulations such that the system does not interfere with retinol skin absorption, nor its clinical efficacy.MethodsAn evaluation tool called the Sustainable Product Optimization Tool (SPOT) was used to assess the environmental performance of formulations containing retinol and the various stabilizers investigated. Accelerated stability tests were performed on formulations stored for 2 months at 4 and 45°C (ISO/TR Standard 18811 2018 directives). Long‐term stability evaluation was done on formulations stored for 24‐months at room temperature. Retinol skin absorption was assessed by the Franz cell method using human skin explants (OECD guideline 428). Finally, a clinical study was performed to evaluate the cosmetic performance of a 0.3% stabilized retinol formulation.ResultsN,N’‐ethylenediamine disuccinic acid ([S,S]‐EDDS isomer) and pentaerythritol tetrakis(3,5‐di‐tert‐butyl‐4‐hydroxyhydrocinnamate) (PBHC) showed higher biodegradability and a reduced water footprint compared with those of BHT and EDTA. The SPOT simulation gave [S,S]‐EDDS + PBHC a score of 10 versus 8.84 for EDTA + BHT. Moreover, [S,S]‐EDDS + PBHC better controlled the chemical degradation of retinol compared with EDTA + BHT. Retinol skin absorption was also achieved in the case of a formulation containing [S,S]‐EDDS + PBHC, and several skin attributes improved significantly after 12 weeks of product use, with over 75% of the panel perceiving benefits.ConclusionRegarding retinol stabilization, the PBHC + [S,S]‐EDDS combination is an eco‐friendlier and more effective alternative to BHT + EDTA.