A three-dimensional nonlinear finite element analysis of the mechanical behavior of tissue engineered intervertebral discs under complex loads.

The use of tissue-engineering method holds great promise for treating degenerative disc disease [Gan JC, Ducheyne P, Vresilovic E, Shapiro IM. J Biomed Mater Res 2000; 51(4): 596-604]. This concept typically implies that nucleus pulposus (NP) cells are seeded on a scaffold, while the NP tissue is regenerated. Such hybrid implant is inserted into the host intervertebral disc. Because the success of a tissue engineering approach depends on maintenance or restoration of the mechanical function of the intervertebral disc, it is useful to study the initial mechanical performance of the disc after implantation of the hybrid. A three-dimensional finite element model (FEM) of the L2-L3 disc-vertebrae unit has been analyzed. The model took into account the material nonlinearities and it imposed different and complex loading conditions. In this study, we validated the model by comparison of its predictions with several sets of experimental data; we determined the optimal Young's modulus as well as the failure strength for the tissue-engineered scaffold under different loading conditions; and we analyzed the effects of implanted scaffold on the mechanical behavior of the intervertebral disc. The results of this study suggest that a well-designed tissue-engineered scaffold preferably has a modulus in the range of 5-10 MPa and a compressive strength exceeding 1.67 MPa. Implanted scaffolds with such properties can then achieve the goal of restoring the disc height and distributing stress under different loading conditions.