Marcolongo Over five million Americans suffer from chronic lower back pain making it the number one cause of lost work days in the United States and one of the most expensive health care issues today. While the causes of lower back pain remain unclear, it is believed that 75% of the cases are associated with degenerative disc disease, where the intervertebral disc of the spine suffers reduced mechanical functionality due to dehydration of the nucleus pulposus. Current treatments include conservative bed rest, discetomy or spinal fusion. Each treatment may be successful in alleviating patient pain, but no current treatment will restore biomechanical function to the disc or prevent further degeneration. Our general premise is that if the initial dehydration of the degenerated nucleus can be arrested and a fully hydrated state returned to the disc, the degenerative process (including the associated pain) would be postponed or prevented and the mechanical function would be restored to the vertebral segment. To accomplish this objective, the investigators propose replacement of the nucleus with a biocompatible, hydrogel polymer implant made from a novel polymer blend of poly vinyl alcohol (PVA) with poly(vinyl pyrrolidone) (PVP). The investigators put forth that the addition of PVP to the PVA will result in a new hydrogel system that will exhibit high stability in vivo and provide adequate mechanical properties while maintaining biocompatibility. The increased stability of these gels is due to hydrogen bonding between the PVA and PVP chains and the formation of interpolymer complexes. In addition, the hydrogel is a memory material, meaning that it can remember or regain geometry from its hydrated to dehydrated states. The investigators will exploit this material property in order to insert the implant into the nuclear cavity arthroscopically, enabling this procedure to be performed in a minimally invasive manner resulting in an approach that is extremely attractive to both patient and surgeon.
For this work, the investigators will establish a relationship between material composition, processing, and properties so that they more fully understand the material behavior of the PVA/PVP hydrogel blends. The dehydration/rehydration characteristics of the hydrogel to establish its feasibility for arthroscopic implantation will be investigated. The investigators will then optimize the hydrogel properties so that the mechanical behavior of a spinal segment with the implanted disc most closely matches that of the intact spinal segment. In this project, the investigators propose to:
1. Synthesize novel co-polymer gels based on PVA and PVP. Characterize the degradation of the hydrogel in vitro to establish the material stability over time as determined by weight loss, changes in surface chemistry and changes in the degree of crystallinity. In addition, the investigators will examine the static mechanical and viscoelastic behavior of the hydrogels as a function of immersion time in vitro.
2. Optimize the dehydration/rehydration conditions of the PVA/PVP hydrogel necessary to facilitate arthroscopic implantation of the disc while retaining adequate mechanical properties.
3. Perform two-dimensional finite element modeling of a simplified lumbar segment to evaluate the effect of implant material properties on stiffness of the lumbar segment under compressive loading as compared to an intact lumbar segment.
4. Compare the biomechanics of a natural lumbar vertebral segment with those after replacement with the hydrogel nucleus in a cadaver model to ascertain the ability of a nuclear prosthesis to restore function to the segment.
