A STROMAL TISSUE CONSTITUTIVE MODEL BASED ON MEASURED COLLAGEN ARCHITECTURE 
Pinsky, P.; van der Heide, D.; Simmons, B.; Chernyak, D.

POLYCONVEX ENERGIES FOR ARTERIAL WALLS, RESIDUAL STRESSES AND DAMAGE
MODELING *
Balzani, D.; Schroeder, J.

We worry about these things for ensuring the existence of minima
Using Fung's exponential models lead to lose of ellipticity
Ball JM, Polyconvexity---Archive for rational mechanics