Fabrication,Characterisation and Tribological Investigation of Artificial Skin Surface Lipid Films |
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Authors: | L-C Gerhardt A Schiller B Müller N D Spencer S Derler |
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Affiliation: | (1) Laboratory for Protection and Physiology, Empa, Swiss Federal Laboratories for Materials Testing and Research, Lerchenfeldstrasse 5, CH-9014 St. Gallen, Switzerland;(2) Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, Zurich, Switzerland;(3) Laboratory for Advanced Fibres, Empa, Swiss Federal Laboratories for Materials Testing and Research, St. Gallen, Switzerland |
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Abstract: | This article deals with the tribology of lipid coatings that resemble those found on human skin. In order to simulate the
lipidic surface chemistry of human skin, an artificial sebum formulation that closely resembles human sebum was spray-coated
onto mechanical skin models in physiologically relevant concentrations (5–100 μg/cm2). Water contact angles and surface free energies (SFEs) showed that model surfaces with ≤25 μg/cm2 lipids appropriately mimic the physico-chemical properties of dry, sebum-poor skin regions. In friction experiments with
a steel ball, lipid-coated model surfaces demonstrated lubrication effects over a wide range of sliding velocities and normal
loads. In friction measurements on model surfaces as a function of lipid-film thickness, a clear minimum in the friction coefficient
(COF) was observed in the case of hydrophilic, high-SFE materials (steel, glass), with the lowest COF (≈0.5) against skin
model surfaces being found at 25 μg/cm2 lipids. For hydrophobic, low-SFE polymers, the COF was considerably lower (0.4 for PP, 0.16 for PTFE) and relatively independent
of the lipid amount, indicating that both the mechanical and surface-chemical properties of the sliders strongly influence
the friction behaviour of the skin-model surfaces. Lipid-coated skin models might be a valuable tool not only for tribologists
but also for cosmetic chemists, in that they allow the objective study of friction, adhesion and wetting behaviour of liquids
and emulsions on simulated skin-surface conditions. |
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Keywords: | Biotribology Skin model Sebum Lubrication Friction Adhesion Deformation Contact-angle Surface free energy Glass Steel Polymers |
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