Effect of human ageing on skin rheology and tribology

Microscopic observations of the human skin have shown that skin topography contains a network of lines whose organization reflects the multidirectional tensions of elastic and collagen fibres in the superficial dermis. This morphology is present at birth and its scale of depth and wavelength increases with age until puberty. The aim of this work is to study how human ageing influences skin morphology, elasticity, loss factor, damping and skin tribology. A complete device to assess the rheology of the skin has been developed. The frequency and strain amplitude range from 10 to 60 Hz and from 1 to 10 μm. An in vivo study including dynamic indentation and tribologic analysis has been performed on 46 subjects aged from 18 to 70 falling into 3 groups. The complex modulus measured by dynamic indentation at 10 Hz frequency stress ranges from 7.17 ± 2.06 kPa for the oldest group to 10.7 ± 2.64 kPa for the youngest group. The combination of the dynamic device with acoustic measurements during friction gives an invaluable help to understand the significance of energy dissipation during friction and shows the impact of skin rheology on acoustic signature during ageing.