Characterization of In-Situ Curing PVA-PEG Hydrogels for Nucleus Pulposus Replacement

Poly(vinyl alcohol) / poly(ethylene glycol) blend formulations are evaluated as an in situ forming gel system. The system will provide a minimally invasive approach to nucleus replacement, whereby a cavity formed in the intervertebral disc post-denucleation is filled via an injectable solution that solidifies to function as prosthetic nucleus pulposus tissue, restoring height, and hydration to the disc, as well as correcting the biomechanics of the spine.;PVA/PEG gels have an inherent system incompatibility that results in the formation of a two phase region, where a water rich supernatant and a polymer rich gel phase form. Systems of dense gels have previously had no simple analytical means for separation of the two similar polymers, particularly at the high viscosities required for this specific application. 1H-NMR analytical techniques are developed for preparation of a %w/w phase diagram. Understanding of possible compositional space enables definition of swelling and stability characteristics for the final gel as it relates to composition. Changes in PEG molecular weight are shown to affect swelling and stability in gels. Upon rheological analysis, a change in the resulting system network with the incorporation of varying types of PVA and PEG is evident. Concentrated gels are shown to display a high temperature reduction in viscosity. This effect is shown to be dependent on molecular weight of the PEG component and gel composition. Similarly, there is a requirement that the system have a low viscosity during the sol stage that shown to be satisfied due to system incompatibility and plasticization effects.