The frictional performance of ex vivo skin was studied in a range of pressures between 0.5 and 20 kPa. Modifications in the coefficient of friction under different conditions stressed the important role of adhesion. The friction coefficient of “untreated” skin was obtained between 2.3–0.5, between 5.5 and 0.65 for wet skin and in a range between 0.65 and 0.35 for oil-covered skin. The contribution of capillary adhesion under wet conditions was analysed by the Hertzian and JKR contact models. The high coefficient of friction obtained under wet conditions could not be explained by the softening effect of the stratum corneum and capillary adhesion only. The results suggested a further influence of water in the physicochemical properties of the stratum corneum with a subsequent effect on friction.@en

Poly(vinyl) alcohol hydrogel (PVA) is a well-known polymer widely used in the medical field due to its biocompatibility properties and easy manufacturing. In this work, the tribo-mechanical properties of PVA-based blocks are studied to evaluate their suitability as a part of a structure simulating the length scale dependence of human skin. Thus, blocks of pure PVA and PVA mixed with Cellulose (PVA-Cel) were synthesised via freezing/thawing cycles and their mechanical properties were determined by Dynamic Mechanical Analysis (DMA) and creep tests. The dynamic tests addressed to elastic moduli between 38 and 50 kPa for the PVA and PVA-Cel, respectively. The fitting of the creep compliance tests in the SLS model confirmed the viscoelastic behaviour of the samples with retardation times of 23 and 16 seconds for the PVA and PVA-Cel, respectively. Micro indentation tests were also achieved and the results indicated elastic moduli in the same range of the dynamic tests. Specifically, values between 45-55 and 56-81 kPa were obtained for the PVA and PVA-Cel samples, respectively. The tribological results indicated values of 0.55 at low forces for the PVA decreasing to 0.13 at higher forces. The PVA-Cel blocks showed lower friction even at low forces with values between 0.2 and 0.07. The implementation of these building blocks in the design of a 2-layered skin model (2LSM) is also presented in this work. The 2LSM was stamped with four different textures and their surface properties were evaluated. The hydration of the 2LSM was also evaluated with a corneometer and the results indicated a gradient of hydration comparable to the human skin.

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