Implicit constitutive equations in the modeling of bimodular materials: An application to biomaterials

Hyaff 11®, a material derived from hyaluronic acid with interesting applications as a scaffold for tissue engineering, is made porous by salt leaching and mechanically tested in simple tension and confined compression. The tests revealed a different behavior in tension and compression, a feature common to other foamed materials. The difference between the behavior in tension and compression is such that the material cannot be modeled with a traditional constitutive law, thus an implicit constitutive equation valid for finite deformations is formulated, and a suitable selectivity criterion is proposed in order to distinguish the behavior in tension from that in compression. The results of the model are compared with the experimental findings both in simple tension and in confined compression, yielding a good fitting with five material parameters.