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

Abstract

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.

Raman comparison of skin dermis of different ages: focus on spectral markers of collagen hydration

“…Among Raman markers of skin hydration, the ratio of the integrated intensities I (3350–3550) /I (2910–2965) (OH stretching vibration of water (ν OH )/CH 3 stretching vibration attributed to skin protein (ν C–H of CH3 )) has been considered in several renowned publications as a reference indicator to measure water in skin and also to assess the moisturizing power of dermo‐cosmetic agents at the level of the stratum corneum and the epidermis . We tested this method to determine the water concentration in our dermal skin samples.…”

“…In addition, Raman spectroscopy was proven to be a sensitive technique to probe the degradation of the stroma by matrix metalloproteinases in basal cell carcinoma . The potential of confocal Raman microspectroscopy for monitoring skin hydration has also been demonstrated . This non‐invasive technique allows in‐depth measurements of the water concentration from the surface to several tens of microns below the skin surface.…”

Changes in Stratum Corneum Thickness, Water Gradients and Hydration by Moisturizers

“…Chrit et al have used confocal Raman spectroscopy to assess the extent of skin hydration changes after using a glycerol-based moisturizing product in vivo [ 34 ] and were able to classify different hydrating products depending on their moisturizing effect on the skin. They showed that a polyphospholipid (poly [2-methacryoyloxylphosphorylcholine or pMPC]) was able to increase water levels in the skin, both in vivo and in vitro, although it should be noted that dosing of the products was not tightly controlled, with any excess product being removed after application and before analysis [ 35 ] . Recently, Förster et al used confocal Raman microscopy to monitor the penetration of retinol into pig skin, and how formulation differences affect penetration [ 36 ] .…”

“…For example, water concentration as it varies across the SC is calculated from ratioing the water signal against the combined signal from water and protein within the skin. This method has also been used to estimate differences in SC thickness in vivo at different body sites and during aging [ 45,46 ] and to evaluate the effects of water and moisturizing ingredients on SC hydration, after both short-term treatment [ 34,47 ] and long-term treatment [ 48 ] . The majority of current research which is using Raman to look at the skin focuses on the SC and upper layers of the viable epidermis, as light becomes increasingly scattered as it penetrates more deeply, reducing signal strength and making data collection more diffi cult.…”

“…Naturally, in the short-term, moisturizers will increase SC hydration given their relatively high water and humectant content [ 34,43,47,[59][60][61] , and in the medium-term improve desquamation [ 62,63 ] . However, in the longer term, it has become apparent that some can actually compromise SC barrier function [64][65][66][67][68] , while others can strengthen it [ 59,61,[69][70][71] .…”