Cartilage repair: surgical techniques and tissue engineering using polysaccharide- and collagen-based biomaterials.

Lesions of articular cartilage have a large variety of causes among which traumatic damage, osteoarthritis and osteochondritis dissecans are the most frequent. Replacement of articular defects in joints has assumed greater importance in recent years. This interest results in large part because cartilage defects cannot adequately heal themselves. Many techniques have been suggested over the last 30 years, but none allows the regeneration of the damaged cartilage, i.e. its replacement by a strictly identical tissue. In the first generation of techniques, relief of pain was the main concern, which could be provided by techniques in which cartilage was replaced by fibrocartilage. Disappointing results led investigators to focus on more appropriate bioregenerative approaches using transplantation of autologous cells into the lesion. Unfortunately, none of these approaches has provided a perfect final solution to the problem. The latest generation of techniques, currently in the developmental or preclinical stages, involve biomaterials for the repair of chondral or osteochondral lesions. Many of these scaffolds are designed to be seeded with chondrocytes or progenitor cells. Among natural and synthetic polymers, collagen- and polysaccharide-based biomaterials have been extensively used. For both these supports, studies have shown that chondrocytes maintain their phenotype when cultured in three dimensions. In both types of culture, a glycosaminoglycan-rich deposit is formed on the surface and in the inner region of the cultured cartilage, and type II collagen synthesis is also observed. Dynamic conditions can also improve the composition of such three-dimensional constructs. Many improvements are still required, however, in a number of key aspects that so far have received only scant attention. These aspects include: adhesion/integration of the graft with the adjacent native cartilage, cell-seeding with genetically-modified cell populations, biomaterials that can be implanted without open joint surgery and combined therapies, aimed at disease modification, pain relief and reduction of inflammation.