The effect of fatigue on associating hydrogels for nucleus pulposus replacement

We have proposed a replacement of the nucleus pulposus with a hydrogel blend of polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP). These hydrogels have been shown to be stable in physiological fluid due to physical crosslinks consisting of intramolecular hydrogen bonds within PVA crystallites and intermolecular hydrogen bonds between PVA and PVP. Much research involving hydrogels has focused on their ability to serve as drug delivery devices, releasing therapeutic agents at controlled release rates. However for a structural application, such as a nucleus pulposus replacement, the hydrogel must be able to withstand repeated loading cycles. Few studies have been conducted that investigate the fatigue behavior of hydrogel materials. Bagga et al. designed a pressurization chamber and compressed PVA hydrogels up to 40 million cycles and observed no changes in the water content or crystallinity of the gels as a result of the fatigue cycling. In this study we examine the physical, mechanical, and chemical properties of cylindrical PVA/PVP hydrogels as a result of compressive fatigue cycling.