Nanomechanical characterization of skin and skin cream.

The mechanical properties of skin are an important characteristic of its resistance to damage and important indicators of pathological situations. Skin care products are the most common method to improve skin health and create a smooth, soft, and elastic perception by altering the mechanical properties of skin. It is of interest to study how skin cream affects the mechanical properties of skin. It also can help to quantify the effectiveness of cosmetic products. In this study, we present a systematic study of the mechanical properties of virgin skin and cream-treated skin. In nanoscratch measurements, the scratch wear tracks were generated at various loads using an atomic force microscope. Hardness and elastic moduli were measured using a nanoindenter. The in situ tensile properties of virgin skin and cream-treated skin were measured using a custom-built tensile stage that attaches to the atomic force microscope. Compared with virgin skin, cream-treated skin exhibits better scratch resistance up to a normal load of 15 μN. The indentation hardness and elastic modulus of cream-treated skin are lower than that of virgin skin, indicating that the skin cream moistens and softens the skin surface. In the stretching experiments, the elastic modulus is lower and ultimate strain is higher than that of virgin skin, indicating skin cream can improve the tensile response of skin. Mechanisms for the observed trends are discussed.