A method to predict the mesoscale contact area for discrete human skin-product surface contacts

A method was developed to predict the contact area between human skin and product surfaces. The method focuses on the mesoscale texture of skin, including primary and secondary lines and related waviness of the skin. This approach aims at discrete human skin – product surface contacts and thus allows the prediction of contact area for individual users or products. Skin features were replicated in a silicone-based compound, and the topography of the replica was measured with confocal microscopy. The numerical core of the method consisted of identifying the individual mesoscale skin structure and digitally representing this structure by fitted semi-ellipsoids. The Hertzian elastic deformation theory was used to calculate resulting contact areas with increasing nominal contact pressure up to 18.3 kPa. The method was validated by measuring the skin surface topography of the volar wrist skin of seven volunteers. The topographies were scaled by a factor 10 and replicated using two types of silicone with different elastic moduli and their contact areas resulting from contact with a flat glass countersurface were measured with a digital fingerprint scanner. It was observed that the measurements and the calculations from the numerical model followed the same trend, where at nominal contact pressures above 9.1 kPa, for most of the volunteers, the model error was below 15 %. The results suggested that the semi-ellipsoid fitting procedure simulates the mesoscale roughness of human skin at moderate contact force conditions, providing a useful approach for modelling contact areas, for example, for future personalized friction studies and product design.