Shear instability in skin tissue

TL;DR

This paper introduces two simplified models to analyze and predict the formation of wrinkles on skin surface under shear, considering tension lines and collagen fiber anisotropy, with explicit criteria for instability onset.

Contribution

It presents novel toy-models that explicitly relate skin's geometrical and material properties to shear-induced wrinkle formation, enhancing understanding of skin mechanics.

Findings

Explicit bifurcation criterion for wrinkle onset

Models account for tension lines and collagen anisotropy

Predicts critical shear deformation for skin instability

Abstract

We propose two toy-models to describe, predict, and interpret the wrinkles appearing on the surface of skin when it is sheared. With the first model, we account for the lines of greatest tension present in human skin by subjecting a layer of soft tissue to a pre-stretch, and for the epidermis by endowing one of the layer's faces with a surface tension. For the second model, we consider an anisotropic model for the skin, to reflect the presence of stiff collagen fibres in a softer elastic matrix. In both cases, we find an explicit bifurcation criterion, linking geometrical and material parameters to a critical shear deformation accompanied by small static wrinkles, with decaying amplitudes normal to the free surface of skin.