4D Numerical Analysis of Scaffolds: A New Approach - Tissue Engineering: Computer Modeling, Biofabrication and Cell Behavior - page 86

Fig. 10 Storage energy vs. axial stretch for 0, 2, 4 and 8 weeks of degradation [ 53 ]

the area (i.e., by taking the integral) underneath the stress-strain curve, from initial
stretch (one) to the desired stretch level (no compression behavior was accessed).
The Neo-Hookean model was the less accurate. However, it never violates the 2nd
Law of Thermodynamics, which imposes that every material parameters μ i must be
positive. The material parameters were calculated by inverse parameterization based
on the experimental data. The results are presented in Table 2 .
If the last degradation stage is discarded, then the material model parameter, μ 1 ,
varies linearly with the hydrolytic damage, as proposed by Soares et al. [ 39 ]. The
proposed approach, which admits that only the first material parameter changes with
hydrolytic damage, μ 1 (d) , according to the linear regressions (see Fig. 11 ), allows
a good description of the mechanical behavior evolution, based on Eqs. ( 24 ), ( 25 )or
( 26 ). Moreover the ultimate stress, which is the failure criterion used, can be defined
by Eq. ( 18 ).
From Fig. 12 , one can see that the hyper elastic material models allowed a rea-
sonable approximation of the tensile test results, i.e. stress vs strain. However, the
constitutive models are unable to describe precisely the initial elastic phase of the