A 3D finite element model of human spine and its mechanical behavior have been modeled. In particular, the mechanical behavior of the last three lumbar vertebras with intervertebral discs (L3-L5 system) has been analyzed. The performance of a new class of prosthetic material used in intervertebral disc substitution treatment has been investigated. This material is a composite made by a matrix of PHEMA poly (2-hydroxyethyl methacrylate) and PCL poly (caprolactone) reinforced with PET poly(ethyl terephthalate) fibers. To perform the comparative analysis, a 3D nonlinear finite element analysis has been implemented. The mechanical behavior (stress-strain curve) of a natural disc and of PHEMA-PCT-PET have been experimentally characterized to obtain the material properties used in the simulations. The results of simulations show that, even if PHEMA-PCT-PET is stiffer than human disc material, the maximum vertical displacement and von Mises stress distribution of the two model systems is comparable. The stresses induced in the discs are higher than the prosthesis but the differences are localized in the cortical region. The different stress distribution induced in the L4 vertebral shows that the vertebral body; after the intervetebral disc substitution, is less stressed by about 19%.
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