IDENTIFICATION AND DETERMINATION OF MATERIAL PROPERTIES FOR POROHYPERELASTIC ANALYSIS OF LARGE ARTERIES

A ''porohyperelastic'' (PHE) material model is described and the theor etical framework presented that allows identification of the necessary material properties functions for soft arterial tissues. A generalize d Fung form is proposed for the PHE constitutive law in which the two fundamental Lagrangian material properties are the effective strain en ergy density function, W-e, and the hydraulic permeability, (k) over t ilde(ij). The PHE model is based on isotropic forms using W-e = U-e(ph i) = 1/2C(0)(e(phi) - 1) and the radial component of permeability, (k) over tilde(RR) = (k) over tilde(RR)(phi), with phi = C-1((I) over bar - 3) + C-2'((I) over bar(2) - 3) + K'(J - 1)(2). The methods for dete rmination of these material properties are illustrated using experimen tal data from in situ rabbit aortas. Three experiments are described t o determine parameters in U-e and (k) over tilde(RR) for the intima an d media of the aortas, i.e., (I) undrained tests to determine C-0, C-1 ', and C-2'; (2) drained tests to determine K'; and (3) steady-state p ressurization tests of intact and de-endothelialized vessels to determ ine intimal and medial permeability (adventitia removed in these model s). Data-reduction procedures are presented that allow determination o f (k) over tilde(RR) for the intima and media and U-e for the media us ing experimental darn. The effectiveness and accuracy of these procedu res are studied using input ''data'' from finite element models genera ted with the ABAQUS program. The isotropic theory and data-reduction m ethods give good approximations for the PHE properties of in situ aort as. These methods can be extended to include arterial tissue remodelin g and anisotropic behavior when appropriate experimental data are avai lable.