Natural surfaces may exhibit remarkable surface properties due to their structure. In the case of skin, its surface topography (microrelief) may influence many of its perceived sensorial properties (shine, color, touch). In order to explore the effects of superimposed biomimetic surface textures on friction, human stratum corneum samples were prepared with and without an imprinted regular 3D grid pattern. The smaller-scale roughness of the samples measured with Atomic Force Microscopy (AFM) and optical profilometry remained when grid lines with a height of 30-40 μm and separation of about 500 μm were introduced. Surface Forces Apparatus (SFA) friction experiments on rehydrated stratum corneum (SC) were performed at low speed (μm/s, back-and-forth sliding) and at more realistic, high speed (cm/s, rotational sliding). Two stratum corneum surfaces in contact did not adhere to one another and had a friction coefficient of 0.1 or less at low sliding speed. They showed an interesting loading-unloading hysteresis with lower friction on unloading, in particular when the contact was on a grid line of the patterned samples. This suggests that the patterning locally induced different mechanical properties of the stratum corneum and that its recovery was not immediate on unloading. When one SC surface slid against a rigid glass surface, the friction force was always higher than the one recorded when two SC surfaces were in contact. However, because of the differences in size of the real contact area between the smooth glass and the stratum corneum with and without pattern, the friction force in the back-and-forth sliding experiments was lower with the imprinted pattern. To further explore the feasibility of texturing skin-like surfaces, films of self-assembling block- and random copolymers were formed on polyurethane substrates with surface topologies that reproduce human skin microrelief (hand, forearm, face). The resulting randomly patterned or randomly rough coatings were characterized with AFM and optical profilometry. The results will be discussed in the light of their cosmetic implications for the development of future skin-care products that could convey properties similar to those found on natural surfaces, such as superhydrophobicity.

Effects of 3D surface patterning on the tribology of human stratum corneum and the topology of a polyurethane skin surface model

253rd National Meeting (2017)

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