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.

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“…After the representative strain value, defined as the squared norm of the median value of the normal strain in the analyzed area, was calculated, a creep curve was generated. The creep phenomenon of biomaterials, such as biological tissue and collagen gel, is generally described using the generalized Kelvin-Voigt model [ 33 , 34 ]. Nonlinear regression of the creep curve of each sample was performed using a three-element model ( Figure 2 f).…”

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“…It is important to note that the Kelvin-Voigt theory is being used in various industrial applications to analyse real materials. For example, Gidde and Pawar [32] use this theory to describe polydimethylsiloxane in a micropump, Jayabal et al [33] employ the theory in connection with modelling skin in the cosmetics industry, while Jozwiak et al [34] describe the dynamic behaviour of biopolymer materials. A very important use of Kelvin-Voigt fluids is in viscous fluid dampers which are employed to reduce the effects of vibrations in civil engineering structures, as analysed by Greco and Marano [35] and Xu et al [36].…”

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“…Our own digital skin platform 8 uses multiscale modeling and virtual reality (VR) for transdermal pharmaceutical and cosmetics delivery [40]. The platform leverages micro-and macro-scale [41] and is capable of in-silico testing [42].…”

“…), they contain active ingredients that interact with skin's mechanical properties (viscoelasticity, young's modulus etc.). To understand the effects of ingredients on skins' mechanical behaviour, Jayabal et al [40] have recently developed a 1D viscoelastic model applied to experimental data for obtaining viscosity and modulus of elasticity of the skin. The authors also demonstrate that the same model can be extended to predict skin behaviour when applied with a polymer layer on Figure 13 shows that property values (enhancement ratio, log P, diffusion coefficient, young's modulus, viscosity etc.)…”