Finite deformation theory for in vivo human skin.

A finite deformation mathematical model of in vivo human skin has been developed for the normal physiological load range. Uniaxial load-deformation measurements were carried out with a non-invasive extensometer and utilized in formulating the model. The in vivo strain energy function was found to be a linear function of the first two strain invariants and a quadratic function of the third strain invariant. Only three independent constants were necessary to specify the strain energy function completely for the upper extremities of human volunteers.