The contributions of skin structural properties to the friction of human finger-pads

This paper describes three series of tests that were designed to investigate how skin mechanical and structural properties, measured using a 'Cutometer' and optical coherence tomography, affect the frictional behaviour of human finger-pads. First, the skin mechanical properties across all fingers and the palm in participants' dominant hands were assessed. Results showed that the distensibility of skin (total deformation in a suction test) is associated with stratum corneum thickness and that this in turn affects friction (thicker stratum corneum leads to higher friction), giving a link between distensibility and friction. Tape stripping to remove the superficial layer of the skin led to increased moisture (and/or electric charge on the skin surface) that led to higher friction. No accompanying changes were seen in structural properties, so it was concluded that moisture was the main cause of the adhesion increase. More work is required to isolate moisture and possible changes in electric charge using alternative measurement techniques. When rubbing with sand-paper, the stratum corneum thinned considerably and friction reduced. Moisture was ruled out as a cause of friction changes in this instance. Skin normal stiffness also did not change, but lateral stiffness changes have been seen in previous work when the stratum corneum thickness has been reduced, so this is likely to be the cause of the reduced friction. This will be investigated further in future work using dynamic optical coherence tomography measurements.