Preparation And Properties Of Associated PVP/PVA Hydrogels For Nucleus Pulposus Replacement

Recently, the most potential treatment to restore the biomechanical function of the spine unit is to replace the central portion of the disc which is called the nucleus pulposus. In this study, PVP/PVA composite hydrogels were prepared by freezing-thawing method. A series of approaches were used to investigate the properties of PVP/PVA hydrogels as the nucleus pulposus replacement. The main contents and results are as follows:1. The PVA/PVP hydrogels prepared by a freezing-thawing method had a porous structure. The porosity increased when the polymerization degree of PVA and content of PVP increased,and the 3-dimensional network structure became denser. The hydrogel bonds formed between PVP and PVA make the interaction and change the arrangement of the molecular chain.2. The crystallinity degree of the hydrogels was investigated by XRD and DSC. Crystallinity degree increases with the degree of PVA polymerization decreased significantly. Adding 1wt% PVP has little effect on crystallinity degree. But when the content of PVP come to 5wt% and 10wt%, crystallinity degree decreased.3. The equilibrium swelling ratio of the hydrogels is more than 400%, and decreased with the degree of PVA polymerization increased.The increasing of PVP content could also increase the swelling ratios of hydrogels. Dried hydrogels' volume reduced by 80% or more than the original samples. When swelling in the second time, hydrogels could be achieved 85% of the maximum degree of swelling in the 48h. The more PVA polymerization degree, the higher of the pH, and the faster of the swelling rate.4. Unconfined compressive mechanical properties of PVP/PVA hydrogels conformed polynominal change rules and exhibited nonlinear behavior. Compressive mechanical strength of hydrogels increased first and then dropped with increasing of PVP content. When the PVA polymerization degree increased, the mechanical strength increased correspondingly. Compressive mechanical strength of the hydrogels coated with UHMWPE fiber rise rapidly. The compressive tangent modulus conformed exponential change, and increased with the PVA polymerization degree increased and PVP content decreased. The modulus of the sample added after coated with the UHMWPE fiber. PVP/ PVA composite hydrogels showed great fatigue properties after 50,000 cycles compressive fatigue test. After fatigue test, the modulus height and mass of the hydrogels could restore to 90% of the original level within 48h. 5. The viscoelastic of the hydrogels was similar to the human's nucleus pulposus. The generalized Maxwell model and generalized Voigt model were established to characterize the stress relaxation and creep behavior of the PVP/PVA gel composites.The stress relaxation speed of the gel composites decreases rapidly with the rise of relaxation time and increases with the rise of initial strain. At the same initial strain, the stress relaxation speed of the gel composites increases firstly and then tent to decrease with the increase of the PVP content. The relaxation propoties of the hydrogels changed dramatically after coating with UHMWPE fiber. The compressive creep properties of the materials were as follows:the creep rate became slower with PVA polymerization degree increased; the hydrogels with lwt%PVP had the largest compliance and the shortest delay time.