Age dependence of mechanical parameters in rat skin following repeated strain

The mechanical parameters of rat skin repeatedly strained with increasing elongation or repeatedly strained with a constant elongation was studied and the hysteresis behaviour was analyzed depending on age. Male Sprague Dawlely rats of an age of 1,2,4, 12, and 24 months were used. Ultimate strain of skin showed a maximum at early adulthood (2 months) whereas the other ultimate values (ultimate load, tensile strength and ultimate modulus of elasticity) exhibited their maxima in late adulthood (4 months). All these ultimate values increased due to maturation and decreased due to senescence. At medium extensions the stress uptake and the elasticity modulus showed a minimum in adulthood. Likewise, in hysteresis experiments both energy dissipation and energy loss at medium extensions exhibited a minimum in adulthood. The ratio between these two parameters, i.e. the relative energy loss was almost independent from age. Residual extension had a minimum at 2 months of age. Therefore, in rat skin the reversibility of deformations had a maximum at early adulthood, stiffness at late adulthood. All those parameters were reversed due to the senescence process.