On the Formulation of Constitutive Equations for Living Soft Tissues*

Soft living tissues deform freely under negligible stresses until a certain strain level is reached at which their stiffness increases sharply. Constitutive equations are developed that describe this kind of mechanical behavior and include Hooke's law as a limiting case. It is shown that, similar to Hooke's law, these constitutive equations assure uniqueness of solution for a broad class of boundary value problems. Possible extensions of the theory are briefly indicated.