Dynamic mechanical response of polyvinyl alcohol-gelatin theta-gels for nucleus pulposus tissue replacement.

Intervertebral disk degeneration is one of the most significant contributors to low back pain. Thus, there is significant interest in designing new treatments and nucleus pulposus (NP) tissue replacements. Herein, the authors propose a biosynthetic material, comprised of a polyvinyl alcohol (PVA) and gelatin theta-gel, as an acellular NP tissue replacement. Theta-gels form during the solidification of PVA and gelatin (phase I), and the phase separation of a disklike short-chain polyethylene glycol (PEG, phase II). The PVA concentration and weight ratio of PVA to PEG were optimized, in order to achieve mechanical properties resembling NP tissue. Mechanical and material properties were analyzed for the PVA-gelatin theta-gels under static and dynamic conditions. Cyclic stress-strain testing demonstrated the theta-gels' ability to relax and perform properly under dynamic loading. Altering the molecular weight and concentration of the theta-gel constituents allows for a tunable material that can match a variety of native tissue properties.