(618b) Analysis of the In Vitro Swelling Behavior of Poly(vinyl alcohol) Hydrogels In Osmotic Pressure Solution for Soft Tissue Replacement

A number of osmotic solutions ranging from 0 atm to 4 atm were used to evaluate poly(vinyl alcohol) (PVA) hydrogels as potential nondegradable soft tissue replacements in vitro. Osmotic solutions were necessary in order to mimic the swelling pressure observed in vivo for soft tissues present in load bearing joints. In vitro studies indicated that PVA hydrogels experience minimal changes in swelling with a polymer concentration of 20 wt% PVA in phosphate buffered saline solution (0 atm) and between 30 and 35 wt% PVA in osmotic solution with a pressure of 0.95 atm. Swelling in osmotic pressure solutions caused decreases in the equilibrium hydrogel hydration. A strong correlation between PVA polymer concentration and swelling ratio was observed; however, swelling ratio was found to be independent of freeze-thaw cycles. This allows for swelling to be tailored through polymer concentration while modulus and porosity is modified using freeze-thaw cycles creating a suite of materials to match a wide range of properties depending on the application desired. An investigation of hydrogel compressive modulus indicated that PVA hydrogels are within the range of articular cartilage, meniscal tissue, and the TMJ disc. The molecular weight between cross-links and microstructure of the PVA hydrogels were also evaluated as a function of freeze-thaw cycles and polymer concentration to lend insight into the processes occurring during synthesis and swelling in osmotic solutions.