Visco-hyperelasticity of Electro-active Soft Tissues

Elastic-electroactive (EA) media represent a wide range of materials and physical systems sensitive to mechanical forces and electric fields, in which time and temperature dependence are additional recurrent features. The behavior of fiber reinforced active tissues, namely the excitation-contraction coupling, is basically due to the nonlinear interplay between the passive elastic tissue and the active muscular network. The observed macroscopic dynamics derives as the emergent behavior of a complex multiscale architecture spanning several length scales. We present a general theoretical framework for the formulation of constitutive equations for viscous electro-active media. The approach is based on the additive decomposition of the Helmholtz free energy in elastic, viscous and active parts accompanied to the multiplicative decomposition of the deformation gradient in elastic, viscus and active parts. We describe a thermodynamically sound scenario that accounts for geometric and material nonlinearities. We specialize the material model to the behavior of colonic intestine tissue, and simulate the visco-electro-active behavior of the fiber-reinforced wall layers by using the finite element method.