Online

Korecki, Casey L.

Mechanical Engineering

2005

MS

Low back pain is a common affliction, affecting approximately 80% of all Americans at some point during their lifetime. Previous work has implicated the intervertebral disc as a major contributor, with many contributing factors such as genetics, aging, and mechanical loading conditions. There are four main methods to study the disc. They include in vivo animal models, in vitro cell culture studies, in vitro mechanical loading studies, and in vitro organ culture studies. Organ culture is appealing because it provides control over mechanical and chemical boundary conditions, keeps the tissue largely intact, and allows interventions that would be impossible or unethical on animal studies. Work on in vitro organ culture has been mostly involved with small animals, or limited to development and validation studies. While small animal studies have many merits, it is desirable to study larger animals where there is more tissue available and issues of nutrient transport are more similar to the human condition. Bovine caudal discs have been shown to be a good model for the human lumbar intervertebral disc, with similar aspect ratios, diffusion distances, compositions, and rates of proteoglycan synthesis. The first aim of this study was to develop a culture system capable of keeping a bovine caudal intervertebral disc alive for at least 8 days while preventing swelling and allowing for application of mechanical compression loading. The second aim was to determine the appropriate baseline loading conditions for future studies. Static and diurnal loading was applied and intervertebral discs were examined after 4 or 8 days with dependent variables including changes in disc height and diameter, tissue water content, tissue proteoglycan content, proteoglycan content lost to the culture media, histological appearance, cell viability, and cell biosynthesis. A decrease in disc height and water content was observed after culture regardless of culture duration or loading condition. Cell viability decreased with culture duration in the inner annulus and nucleus, however, the nucleus pulposus also had a reduction in viability for the diurnal loading condition as compared to static. No significant differences were seen in viability of the outer annulus for any loading groups. In conclusion, an organ culture system was developed capable of keeping a bovine caudal disc alive for 8 days without significant changes in GAG content, cell viability, and cell metabolism. This system offers promise for the future study of intervertebral disc mechanobiology. Static loading was determined to be the best baseline loading condition because it better maintained cell viability in the nucleus pulposus, and was less prone to technical difficulties. Future studies will examine the role of dynamic loading on the mechanobiological response of the intervertebral disc in order to evaluate how damaging loads affect dependent variables developed in this study.