A novel method to measure skin mechanical properties with three-dimensional digital image correlation.

BACKGROUND: Measuring skin mechanical properties has been of great interest in the skincare industry. It is a high accuracy and non-invasive optical technique which quantitatively tracks skin movement and deformation under mechanical perturbations. METHODS: A study was conducted with female subjects (25-65 years old). A refined speckle pattern applied onto the skin surface was used for DIC measurements. A unidirectional force pulled the skin at a constant velocity, while the deformation process was quantified by the DIC. Prior to the DIC measurement, Cutometer® readings were taken on the same area. The DIC protocol's reproducibility across multiple pattern applications, the measurement's repeatability, and the sensitivity in differentiating skin mechanical properties were investigated. RESULTS: Subjects were clustered with statistical significance according to their skin mechanical properties described by six DIC metrics (µ [major strain], σ [major strain], µ [minor strain], σ [minor strain], µ [displacement], and σ [displacement]). Most measurement random errors are below 6%. This is several folds smaller in magnitude than the difference in the mean response between the clusters. Several Cutometer® parameters also showed good agreement with µ (displacement). CONCLUSIONS: DIC was able to differentiate skins of different mechanical qualities. We also proposed the physical significance of the DIC metrics. Some of the DIC metrics potentially offer new insights into skin mechanical properties that complement those revealed by conventional instruments. Accurate measurements, large measurement areas along with ease of direct visualization are substantial advantages of DIC.

The effect of N-acetyl-glucosamine on stratum corneum desquamation and water content in human skin.

Alpha-hydroxy acids have been used topically to treat skin for both dermatological and cosmetic problems for many years. Though there are many known benefits of the use of alpha-hydroxy acids on skin, there have been recent reports that topical treatments with alpha-hydroxy acids increase skin damage resulting from UVB. Additionally, high concentrations of alpha-hydroxy acids by themselves have also been found to cause skin irritation. In order to find alternatives to alpha-hydroxy acids, we investigated a variety of amino sugar compounds that were previously reported to inhibit the reaggregation of dissociated corneocytes by modulating cellular adhesion. In vivo, we observed that topical treatments with a formulation containing N-acetyl-glucosamine (NAG) led to an increase in skin moisturization, a decrease in skin flakiness, and the normalization of stratum corneum exfoliation. In vitro, we observed an upregulation of differentiation markers, keratin 10 and involucrin, in keratinocytes treated with NAG. CD44 is a lectin cell adhesion molecule that is also expressed in keratinocytes. Amino sugars such as NAG may competitively bind to CD44, modulating keratinocyte cellular adhesion. We hypothesize that these amino sugars modulate keratinocyte cellular adhesion and differentiation, leading to the normalization of stratum corneum exfoliation. We propose the use of amino sugars such as NAG as alternative compounds to replace the use of alpha-hydroxy acids in skin care.

Cigarette smoke-induced lipid peroxidation in human skin and its inhibition by topically applied antioxidants.

Cigarette smoke, whether indirect or direct stream, is an environmental pollutant which presents an increasing health problem. In order to determine damage to human skin at the biochemical level, volar forearms were exposed to cigarette smoke for fifteen minutes and then assayed for the presence of stratum corneum lipid peroxides. A time-dependent increase was observed over a 24-hour post-exposure period. At 24 h, the average baseline level of lipid peroxides was 14.9 nmol/unit area of skin as compared to 32.0 nmol/unit area of skin for the smoke-exposed arms. In addition, when topical antioxidants were pre-applied to the skin and then exposed to cigarette smoke, an average decrease of 40.9% in lipid peroxide values was observed. These data demonstrate that peroxidation was induced in human skin by cigarette smoke and subsequently inhibited by the presence of antioxidants.