Elucidating the mechanistic process of age induced human skin wrinkling

While it is universally known that chronological ageing results in the formation of skin wrinkles, currently the mechanistic process by which they form is not well understood. Contemporary studies modeling the formation of wrinkles rely on computational and theoretical models, and to date, no comprehensive experimental study has been completed that can adequately explain why wrinkles form, nor validate prior studies. This study addresses this knowledge gap by capturing differences in the mechanical behavior and surface topography of ex-vivo human skin across a diverse range of ages, subjected to residual stresses consistent with in-vivo loading conditions; tension aligned with the dominant collagen orientation. These responses are contrasted with mechanical and topographical responses when tensile loads are applied perpendicular to the dominant collagen orientation. Changes in axial and transverse strains, inflection point strains, and Poisson's ratios are first characterized as a function of age. The depth, width, and tortuosity of subsequent wrinkles are then subsequently quantified. Transverse contractile strains resulting from applied axial loading increase with age, resulting in the formation of deeper and wider wrinkles with striations parallel to the axis of loading. This study also demonstrates that full thickness ex-vivo skin tissue can exhibit a Poisson's ratio greater than ν=0.5, with increasing magnitudes with age progression. This indicates that when loaded, skin must undergo a poroelastic negative volumetric change, which is then verified through liquid desorption studies.