#### Vol. 7, No. 7, 2012

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Characterization of human skin through skin expansion

### Djenane C. Pamplona and Claudio R. Carvalho

Vol. 7 (2012), No. 7, 641–655
##### Abstract

This study characterized human skin of the lower leg and scalp during the surgical process of skin expansion. To our knowledge, this is the first study in this field, which has provided results that considerably improve our understanding of human skin. A detailed in vivo analysis was carried out involving four different patients that allowed for observation during the relaxation process. A comparison between the in vivo and numerical finite elements model of the expansion was used to identify the material elastic parameters of the skin. After a comprehensive search of constitutive equations for describing skin, Delfino’s constitutive equation was chosen to model the in vivo results. We considered skin as an isotropic, homogeneous, hyperelastic, and incompressible membrane. The parameters of Delfino’s exponential function obtained for the first skin stretch process were $a$ = 40.0 KPa and $b$ = 20.2. As skin is extended, such as with expanders or in other procedures that tighten the skin, the collagen fibers are also extended and cause stiffening in the skin, which results in it being more and more resistant to expansion or further stretching. We observed this phenomenon as an increase in parameters $a$ and $b$ as subsequent expansions continued. The results of this study allow for the quantification of stiffening of the skin after several stretches, when the skin becomes more and more inelastic. These results are very encouraging and provide insight into our understanding of the behavior of stretched skin and maybe other biological tissues, as swollen artery and veins.

##### Keywords
characterization of human skin, finite elements, skin expansion, biomembranes, constitutive equation