FEATURE COSMETICS
Skin deep: optical tests scrutinise beauty claims
More than ever, optics are critical to testing the cosmetic industry’s never-ending supply of promises, reports Rebecca Pool
F
rom wrinkle removal and plumping power, to instant hydration and antioxidant action, ever more cosmetics are flooding the market
with claims of combatting the inevitable signs of ageing. Given this, cosmetic testing houses are turning to a range of optics- based methods to assess if ingredients and products are safe, and truly live up to the hype. For Dr Nikita Radionov, commercial
manager at Laboratoire Bio-EC, microscopy is a firm favourite. As he puts it: ‘Be it hydration studies, anti-ageing studies, many labs can perform clinical studies for cosmetic products but microscopic analysis produces very robust results and convincing evidence [of a product’s efficacy].’
During in vivo clinical studies, skin
samples can be taken from volunteers using strips of tape that remove the three or four outermost stratum corneum layers of the skin. In a typical scenario, researchers may be testing the efficacy of a skin barrier repair product, where the replenishment of skin lipids can be deemed a desirable therapeutic target. Here, immunostaining of samples for light microscopy can reveal structures in the samples such as filaggrin, a filament aggregating protein that binds to
12 Electro Optics July 2021
keratin fibres in epithelial skin cells, and ceramides, waxy lipids that link molecules and create a barrier to prevent permeability. Bio-EC researchers also work with Bordeaux Imaging Centre, using electron microscopy to analyse the skin samples and garner detail on the organisation of, say, ceramide, lipids and sebum in that sample. ‘The microscopy results we get are so visual and convincing, and tell a story,’ said Radionov. ‘For example with melanin analysis we can take an image of the corneal site [on an epidermal layer] and see the tiny black granules of melanin inside the cell. ‘We can also visualise all the damaged
proteins on the skin surface – if a product protects against oxidative stress, we can use images of protein damage to compare the results before and after its use,’ he added.
But beyond the more traditional
fluorescence and electron microscopy methods, researchers are developing techniques to study skin further. For example, researchers have been optically clearing small skin samples, using clarification methods such as 3Disco – 3D imaging of solvent-cleared organs – to render samples transparent. These samples can then be analysed using a range of light microscopy methods.
In a recent example, researchers Eric
Fernandez and Sylvie Marull-Tufeu, from the Laboratoire Application Cutanée, Yves Rocher, worked with biopsy punches from human abdominal skin taken after plastic surgery. The samples were stained with the fluorescence dye Rhodamine B, and then cleared, with the transparent samples analysed using laser scanning confocal microscopy. Using their technique, Fernandez and Marull-Tufeu visualised the micro- architecture of the epidermis at different skin depths – from the outermost stratum corneum layer to the deeper papillary dermis. And they also went on to reconstruct the entire epidermis in 3D, showing exactly how complex the skin is. As Fernandez and Marull-Tufeu wrote in Skin Research and Technology: ‘This
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