A method for the determination of mechanical parameters in a porous elastically deformable medium : applications to biological soft tissues

further approach has been tentatively envisaged for the determination of the mech! anical parameters characterizing the unsteady behaviour of soft biological tissues considered as porous\ elastically deformable media\ saturated with a viscous ~uid[ If the two solid and ~uid phases are incompressible\ the parameters to be determined are ] the drained Young|s modulus and Poisson|s ratio\ the permeability of the porous solid structure and the dynamic viscosity of the interstitial ~uid[ Standard ramp relaxation tests have been performed in order to investigate the time evolution of the force acting upon tissular disco( dal samples subjected to uncon_ned compressive strainsunder controlled environmental conditions[ For moderate compressive strains\ such a response in resultant force\ characterizing a stress di}usion phenomenon within the medium\ can be analyzed using a spectral decomposition with orthogonal eigenvectors[ Such an analysis reveals that the overall response is de_ned by its asymptotic behaviour during both compression and relaxation phases\ leading to the evaluation of the Young|s modulus and Poisson|s ratio[ Moreover\ the determination of the relaxation time leads to the evaluation of the speci_c permeability of the structure*the dynamic viscosity of the ~uid being already known[ A few examples of experimental tests data\ involving both rubber foam\ myocardium tissue in passive state and _broblastic biological collagenic gels\ are presented here in order to illustrate and validate such a rheological methodology[ Particular attention is paid to the relations between the poroelastic behaviour and microstructural parameters of the material\ with an emphasis on possible nonlinear e}ects arising from these very deformable media[ 0887 Elsevier Science Ltd[ All rights reserved[