Canine chondrocytes seeded in type I and type II collagen implants investigated in vitro

Synthetic and natural absorbable polymers have been used as vehicles for implantation of cells into cartilage defects to promote regeneration of the articular joint surface. Implants should provide a pore structure that allows cell adhesion and growth, and not provoke inflammation or toxicity when implanted in vivo. The scaffold should be absorbable and the degradation should match the rate of tissue regeneration. To facilitate cartilage repair the chemical structure and pore architecture of the matrix should allow the seeded cells to maintain the chondrocytic phenotype, characterized by synthesis of cartilage-specific proteins. We investigated the behavior of canine chondrocytes in two spongelike matrices in vitro: a collagen-glycosaminoglycan (GAG) copolymer produced from bovine hide consisting of type I collagen and a porous scaffold made of type II collagen by extraction of porcine cartilage. Canine chondrocytes were seeded on both types of matrices and cultured for 3 h, 7 days, and 14 days. The histology of chondrocyte-seeded implants showed a significantly higher percentage of cells with spherical morphology, consistent with chondrocytic morphology, in the type II sponge at each time point. Pericellular matrix stained for proteoglycans and for type II collagen after 14 days. Biochemical analysis of the cell seeded sponges for GAG and DNA content showed increases with time. At day 14 there was a significantly higher amount of DNA and GAG in the type II matrix. This is the first study that directly compares the behavior of chondrocytes in type I and type II collagen matrices. The type II matrix may be of value as a vehicle for chondrocyte implantation on the basis of the higher percentage of chondrocytes retaining spherical morphology and greater biosynthetic activity that was reflected in the greater increase of GAG content.