A linear viscoelastic model to understand skin mechanical behaviour and for cosmetic formulation design

Abstract

OBJECTIVES: Skin is arguably one of the most important organs that plays an active role in our everyday biological functions after brain. Owing to the wide range of applications in medicine, cosmetics industry and more recently robotics, skin research has gained tremendous attention with respect to its mechanical behaviour. Various macro modelling approaches are available for modelling skin's mechanical behaviour. The objective of this paper is to study skin's mechanical property change with age and demonstrate anti-ageing effects of cosmetic formulations from skin mechanical property change perspective. METHODS: In this study, skin's mechanical behaviour was modelled using a 1D linear viscoelastic phenomenological model and the model was validated using two sets of experimentally observed skin data (strain, stress relaxation and cyclical loading). The model was further modified to study the effect of the presence of a thin layer of cosmetic polymer and to demonstrate anti-ageing effects of the cosmetic polymer from the perspective of change in the mechanical behaviour of skin with cosmetic layer. RESULTS: The estimated values of skin mechanical properties from the model agree with those in literature. The extracted model features show good correlation with skin age (viscosity and time constant). The results from our model indicate that the cosmetic polymers enhance the mechanical properties of skin significantly. CONCLUSIONS: This work will find its applications in designing and testing anti-ageing formulations. This model can be used to filter various combinations of cosmetic formulations by knowing the mechanical response of polymer on skin, thereby accelerating the product development.