Introduction of Human Skin Prestress: Effect on the Wave Propagation Velocity

Characterization of human skin properties is more and more intriguing scientists as it is an nonlinear anisotropic material. This mechanical behavior can be justified by the presence of collagen fibers. These fibers induce a natural prestress responsible of aging and anisotropy of the skin. Therefore, the present paper proposes an insight into the study of a new intrinsic human skin characteristic, which is the natural prestress of the cutaneous tissue. The purpose of this work is to distance the relation between human skin natural prestress and wave propagation velocity in the surface of the skin. To this aim, a 3D model based on the Finite Element Method (FEM) was developed. The skin is modeled by a stratified 3D volume with two layers. The cutaneous tissue is considered as an isotropic linear elastic material. The upper outer surface is subjected to a mechanical impact inducing a surface wave that propagates throughout the surface. The wave propagation velocity is calculated along a path on the surface of the FE model. The influence of the human skin prestress on the velocity of the wave propagation is investigated. A major conclusion states that the prestress slows down the wave propagation. Thus, the wave propagation velocity decreases when the prestress increases. The skin soaks the loading and is then similar to an elastic trampoline.