title: A new water absorbable mechanical Epidermal skin equivalent: the combination of hydrophobic PDMS and hydrophilic PVA hydrogel.
abstract: Research on human skin interactions with healthcare and lifestyle products is a topic continuously attracting scientific studies over the past years. It is possible to evaluate skin mechanical properties based on human or animal experimentation, yet in addition to possible ethical issues, these samples are hard to obtain, expensive and give rise to highly variable results. Therefore, the design of a skin equivalent is essential. This paper describes the design and characterization of a new Epidermal Skin Equivalent (ESE). The material resembles the properties of epidermis and is a first approach to mimic the mechanical properties of the human skin structure, variable with the length scale. The ESE is based on a mixture of Polydimethyl Siloxane (PDMS) and Polyvinyl Alcohol (PVA) hydrogel cross-linked with Glutaraldehyde (GA). It was chemically characterized by XPS and FTIR measurements and its cross section was observed by macroscopy and cryoSEM. Confocal Microscope analysis on the surface of the ESE showed an arithmetic roughness (Ra) between 14-16 μm and contact angle (CA) values between 50-60°, both of which are close to the values of in vivo human skins reported in the literature. The Equilibrium Water Content (ECW) was around 33.8% and Thermo Gravimetric Analysis (TGA) confirmed the composition of the ESE samples. Moreover, the mechanical performance was determined by indentation tests and Dynamo Thermo Mechanical Analysis (DTMA) shear measurements. The indentation results were in good agreement with that of the target epidermis reported in the literature with an elastic modulus between 0.1-1.5 MPa and it showed dependency on the water content. According to the DTMA measurements, the ESE exhibits a viscoelastic behavior, with a shear modulus between 1-2.5MPa variable with temperature, frequency and the hydration of the samples.
authors.affiliation: Surface Technology and Tribology Group, University of Twente, Drienerlolaan 5, 7522 NB PO Box 217 7500 AE Enschede, The Netherlands. Electronic address: m.moraleshurtado@utwente.nl.
authors.forename: M
authors.initials: M
authors.lastname: Morales-Hurtado
authors.affiliation: Surface Technology and Tribology Group, University of Twente, Drienerlolaan 5, 7522 NB PO Box 217 7500 AE Enschede, The Netherlands.
authors.forename: X
authors.initials: X
authors.lastname: Zeng
authors.affiliation: Inorganic Materials Science, University of Twente, Drienerlolaan 5, 7522 NB Enschede, The Netherlands; Materials innovation institute (M2i), Mekelweg 2 2628 CD Delft, The Netherlands.
authors.forename: P
authors.initials: P
authors.lastname: Gonzalez-Rodriguez
authors.affiliation: Inorganic Materials Science, University of Twente, Drienerlolaan 5, 7522 NB Enschede, The Netherlands.
authors.forename: J E
authors.initials: JE
authors.lastname: Ten Elshof
authors.affiliation: Surface Technology and Tribology Group, University of Twente, Drienerlolaan 5, 7522 NB PO Box 217 7500 AE Enschede, The Netherlands; TNO, PO Box 6235, 5600 HE, Eindhoven, The Netherlands.
authors.forename: E
authors.initials: E
authors.lastname: van der Heide
mesh_terms: D065966:Absorption, Physicochemical; D040761:Biomimetic Materials / Q000737:chemistry*; D004129:Dimethylpolysiloxanes / Q000737:chemistry*; D055119:Elastic Modulus; D004817:Epidermis; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D011142:Polyvinyl Alcohol / Q000737:chemistry*; D013499:Surface Properties; D014783:Viscosity; D014867:Water / Q000737:chemistry*
chemical_list: D004129:Dimethylpolysiloxanes; C062364:polyvinyl alcohol hydrogel; D014867:Water; C013830:baysilon; D011142:Polyvinyl Alcohol
keywords: Elastic modulus; Hydration; Polydimethyl Siloxane; Polyvinyl Alcohol hydrogel; Skin equivalent; Skin tribology