In vitro and in vivo confocal Raman study of human skin hydration: assessment of a new moisturizing agent, pMPC

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.