Effects of Imprinted 3D Surface Patterning on Localized Changes in the Tribology of Human Stratum Corneum

Natural surfaces may exhibit remarkable surface properties due to their structure. In the case of skin, its surface topography (microrelief) influences many of its perceived sensorial properties (shine, color, touch). Imprinted patterns can modify the original microrelief, inducing a completely new set of perceived properties. To explore the effects of superimposed biomimetic surface textures on the friction of skin, human stratum corneum was prepared with and without an imprinted regular, micrometer-sized, 3D grid pattern. Atomic Force Microscopy (AFM) and optical profilometry indicated that the inherent, smaller-scale roughness of the stratum corneum remained when lines with heights of 20-200 μm and spacings of 600-2000 μm were introduced, but it was somewhat reduced on the grid lines. Surface Forces Apparatus (SFA) friction experiments on stratum corneum 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 they had a friction coefficient μ of 0.1, or lower, at low sliding speed. An interesting loading-unloading hysteresis was observed, with lower friction force 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 stratum corneum surface slid against a rigid glass surface, the friction coefficient was always higher than that when two stratum corneum surfaces were in contact. At high sliding speed, much higher friction coefficients were found between one stratum corneum surface and a rigid, smooth surface, μ ≥ 1. The results demonstrate that topograpic patterning by imprinting clearly modifies the tribological response of stratum corneum. This approach provides a simple method for exploring the development of biomimetic modifications of skin texture.