Nonlinear visco-elasticity of soft tissues under cyclic deformations

Nowadays, new experimental set-ups allow to determine the strains which appear in biological tissues under small controlled solicitations as stretch (uniaxial and bi-axial) or shear. Automatically recorded by camera, these data exhibit hysteresis even for very slow and weak forcing. The aim of this work is to revisit the modeling of hyper-elasticity and visco-elasticity for tissues with a rather disordered structure. Despite the weakness of the imposed stretch values, strong nonlinearities are observed for these tissues that polymeric gels do not show under the same conditions. Various classical models have been tested on surgical mammary tissues and it turns out that the simplest Neo-Hookean model with its viscous counter-part explain perfectly the data. Viscosity and elasticity compete quite equivalently showing that, in the selected range of forcing values, visco-elasticity cannot be discarded.