A structural model used to evaluate the changing microstructure of maturing rat skin.

A microstructurally based model for soft biological tissues was adapted to model the non-linear response of the collagenous network in skin. Quasi-static uniaxial tensile tests were conducted on dorsal skin of rats aged 1-4 months. Specimens were taken longitudinally and transversely (laterally) to the spine and tested at 1.5% s-1. The model showed fiber stiffness to increase laterally during maturation and to be greater laterally than longitudinally. It also indicated the migration of the 'heel' portion of the response curve toward the origin during maturation to be due to less crimping in the fibers. These results were qualitatively supported by microscopical observations. The model was found to be well suited to fit response curves exhibiting a well-defined 'heel' region. For curves exhibiting a more flat, featureless 'heel' region (typical of 1 month longitudinal specimens) the model was not well suited. The results of this study indicate that this simple three-parameter model might be a useful tool in future studies to analyze pathological changes in the collagenous microstructure.