A characteristic sign of aging skin is loss of firmness. Current bioinstruments to measure the influence of formulations on skin mechanics are limited in sensitivity and have high operator variability. To address these issues an optical elastography system was developed. Regions of the upper inner bicep were treated with various commercial formulations including wrinkle reducers, firming films, and moisturizers. These regions along with adjacent untreated areas that served as internal controls were imaged with a custom designed optical elastography system. The elastography system employed a polarized 50 mW 532 nm cw laser as an illumination source, a CCD camera imaging the skin at 160 Hz frame rate and a polarization analyzer aligned parallel to the incident beam. The skin was mechanically loaded using compressed air reduced in pressure and modulated using a proportional valve to provide a 1 Hz sinusoidally varying pressure to the skin with a peak force of 0.15 N. Subjects ranging in ages from 19 to 60 years old were recruited with IRB approval. Displacement and strain encoded elastograms were generated simultaneously for the treated and untreated areas. The ratio of the strain response in the two regions was calculated to quantify the relative effect of the skin agents. Significant differences were found in the strain response to the imposed loads between treated and control areas in all age groups and genders. Optical elastography systems such as the one prototyped in this study may prove to be useful for the cosmetics industry for assessing product efficacy.
The epidermis is the outermost layer of skin and is composed of cells primarily containing keratin. It consists of about ten layers of living cells (keratinocytes) and ten layers of dead cells (corneocytes). These cells are continually shed from the outside and replaced from the inside in a process called desquamation which is controlled by two biological events – proliferation and differentiation.
One method to non-invasively study biological changes in the skin is using fluorescence excitation spectroscopy. Several characteristic excitation-emission peaks occur in skin that have been related to the epidermal and dermal composition. The magnitude of the peak that occurs at 295nm excitation (F295) has been linked to changes in skin proliferation, cell turnover, epidermal thickening, and skin aging. We hypothesize that changes in this fluorescent signal could be used to assess the potential activity of cosmetic anti-aging compounds to deliver a benefit to skin.
Previous work with retinol and glycolic acid, two commonly used actives that effect epidermal proliferation and exfoliation, has demonstrated an increase in F295 (attributed to tryptophan excitation fluorescence). In this study we present the results of a placebo controlled study that aims to correlate changes in F295 with biological performance (epidermal thickening and Ki67 expression).
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