Graduation date: 2007Hydrogels have been proposed as candidates for nucleus pulposus replacement due to their similarity in mechanical behavior to the native tissue when subjected to transient or static loading; however, given the viscoelastic nature of soft biological tissues, the lack of dynamic testing is a significant inadequacy in the studies performed to date. Our goal was to identify hydrogel systems whose viscoelastic behavior, particularly under dynamic torsional shear, mimicked that of the native tissue. Hydrogels were formed via photopolymerization of glycidyl methacrylate and 1,2-epoxy-5-hexene modified poly(vinyl alcohol) and were allowed to equilibrate in Hank’s solution prior to analysis. The viscoelastic behavior of all prepared materials was compared with that of sheep nucleus pulposi. Complex shear moduli and phase shift angles were determined from dynamic frequency sweeps in torsional shear. Resistance towards hydrolysis was assessed by evaluation of the viscoelastic behavior of hydrogels submerged in Hank’s solution for progressively longer periods of time. For glycidyl methacrylate-PVA hydrogels the viscoelastic parameters could be modulated by varying the molecular weight of PVA and the concentration of polymer prior to photopolymerization. The mechanical behavior of 1,2-epoxy-5-hexene-PVA hydrogels could be regulated in a similar manner by altering the type and percentage of monomer used to induce polymerization. The phase shift angles of all hydrogels were lower than those of the nucleus pulposi; however, the complex shear moduli of both synthetic systems spanned the values observed for the natural system. Over the time frame of the experiment, no change in moduli was observed following submersion in Hank’s solution. This study represents the first attempt to successfully mimic the viscoelastic nature of the nucleus pulposus exhibited under dynamic torsional loading with that of materials intended for use in tissue replacement.