[Biomechanical studies of human and animal skin in vivo and in vitro].

With the help of biomechanical and biochemical methods, the dependence of human and rat skin on maturation and aging could be demonstrated in excised samples. Ultimate load, tensile strength, and modulus of elasticity showed a sharp increase during maturation and a slow decrease during aging, in both rat and human skin. In both species, ultimate extension revealed a similar behaviour, but the increase during maturation was less pronounced. The age-depending changes of the mechanical parameters in rat skin were influenced by anisotropic properties, which at least partially could be explained by the existence of the skin muscle layer in rats. Tensile strength of skin was closely correlated with the contents of insoluble collagen, e.g. the degree of cross linking. There was, however, no correlation between tensile strength and the contents of soluble collagen, glycosaminoglycans, or elastin. Further experiments like hysteresis, relaxation, and creeping behaviour indicated that plasticity and viscosity of skin both decrease during maturation and aging. Taking into account the experimental conditions, the results gained "in vivo" correlate with those obtained "in vitro".