Microtribological and micromechanical properties of the skin stratum corneum

The stratum corneum is the outermost layer of mammalian skin, serves as a penetration, dehydration, and protection barrier against various environmental hazards. In this article, the microtribological and dynamic micromechanical properties of stratum corneum are studied. The rat stratum corneum is chosen as the animal model. In the microtribological tests, it is found that the coefficient of friction of stratum corneum decreases with the increasing of normal load and a linear viscoelastic contact model of stratum corneum is developed. In the dynamic micromechanical tests, the results show that there are initial maxima in storage (E′) and loss (E″) moduli with both increasing of frequency and penetration depth. After the maxima, there are marked decreases in storage and loss moduli with increasing of frequency and penetration depth. It is suggested that this decrease is due to a water gradient across the stratum corneum. In addition, although the loss modulus is less than the storage modulus, there is a gradual increase in their ratio with increasing of displacement into stratum corneum. This indicates a shift toward more viscous behavior. This study provides key stratum corneum tribological and mechanical properties when moving on and penetrating into stratum corneum for the exploitation of drug delivery systems, artificial skin, textile, skin care production, and other studies related to stratum corneum.