Mechanical characterization of polypropylene reinforced poly(vinyl alcohol) hydrogels for fibrocartilage replacement

Poly(vinyl alcohol) (PVA) based hydrogels are ideal for biomaterial applications in that they allow for the formation of physical cross-links during freeze-thaw cycling without any need for possibly toxic monomers. PVA hydrogels have been investigated extensively for articular cartilage applications due to their ability to mimic human tissue. Poor properties in tension, however, limit the actual use of this material. In this study, poly(vinyl alcohol) (PVA) hydrogels were reinforced with polypropylene (PP) fibers and evaluated as possible fibrocartilage replacements. An investigation of hydrogel and composite mechanical properties indicates PP-reinforced PVA hydrogels could replicate the radial modulus present in the native meniscus; the most commonly damaged orthopedic tissue. More specifically, fibrous reinforcement successfully increased the tensile modulus of the biomaterial from 0.25 MPa without any reinforcement to 8 MPa at 10 vol% PP. Additionally, the molecular weight between cross-links and microstructure of the PVA hydrogels were evaluated as a function of freeze-thaw cycles to lend insight into the processes occurring during synthesis. These results suggest the presence of multiple mechanisms as possible causes for increasing hydrogel modulus with freeze-thaw cycling.