Semi-degradable, multi-functional hydrogels for the repair of articular cartilage defects

Cartilage cannot undergo spontaneous repair because of a lack of access to the blood supply, so cartilage defects progressively deteriorate into osteoarthritis. The typical approach for tissue engineering is the cultivation of cells on degradable scaffolds such as poly(glycolic acid) (PGA). The cartilage tissue that results from this method integrates well with surrounding tissue when implanted into cartilage defects. However, the mechanical and biochemical properties are inferior to healthy cartilage, and the tissue eventually degrades. Poly(vinyl alcohol) (PVA) hydrogels, on the other hand, have long been studied for cartilage replacement because of their similar mechanical and material properties, but their complete lack of integration with surrounding cartilage as implants has impeded their utility.;The combination of the integrative properties of PGA scaffolds with the mechanical properties of PVA hydrogels may allow their use as implants. PVA hydrogels were made porous through a novel technique of microparticle incorporation. Average pore sizes ranged from 60 to 300microm. Cartilage cells could be seeded throughout the porous network and induced to develop healthy cartilage tissue. Since PVA hydrogels are nondegradable, the result was a hybrid hydrogel-cartilage construct that may integrate well with surrounding tissue. Moreover, the nondegradable nature of the PVA hydrogel would prevent the mechanical properties from diminishing over time, as is the case with degradable scaffolds. These superporous, semi-degradable hydrogels were evaluated as cartilage replacement materials in terms of their dynamic structure, mechanical properties, and swelling properties, over the course of swelling in model osmotically-conditioned systems. The hydrogels were then characterized for their ability to support cartilage formation by encapsulated cells and the effects of controlled release of growth factors to enhance cartilage formation and integration between the hydrogels and the surrounding tissue.;The results demonstrate that these PVA-based hydrogels have the potential to effectively replace damaged cartilage, because they have similar mechanical and swelling properties that are stable over the long-term, and support cartilage formation and integration with surrounding tissue. A novel technique is also described for evaluating the swelling properties of biomaterials in a model system that can be applied to many other types of biomaterials and tissues.