Abstract
The nucleus pulposus of lumbar intervertebral discs is composed of a solid phase which includes collagen and proteogrycan and a fluid phase which includes interstitial fluid. When an external load is applied to an intervertebral disc, interstitial fluid passes between the cells of the solid phase. Then, frictional force occurs and induces the macroscopic nonlinear viscpelastic behavior of a disc. In this study, we examined the biphasic behavior of the nucleus pulposus under uni-axial confined compression. Permeability, which explains the interaction between two phases, was estimated from stress-relaxation behavior by using biphasic theory proposed by Mow V.C. et al. By modeling nucleus pulposus as biphasic material, we simulated the viscoelastic behavior of the intervertebral disc using a finite element analysis. In the relaxation process, the redistribution of the strain, change in the drag force and the relaxation stress could be observed by this simulation.
