The use of absorbable co-polymer pads with alginate and cells for articular cartilage repair in rabbits

PURPOSE: To determine the effect of polyglycolic acid (PGA)-polylactic acid (PLA) co-polymer pads with calcium alginate on chondrogenic gene expression for chondrocytes cultured in vitro. We also evaluated the ability of these absorbable pads with alginate to deliver chondrocytes and influence osteochondral defect repair in vivo in immature rabbit knees. METHODS: Rabbit rib chondrocytes were suspended in calcium alginate and co-polymer pads composed of either 47.5/52.5 PGA-PLA or 90/10 PGA-PLA at two different cell concentrations and cultured in vitro for 1, 3, and 5 days. Analysis was performed using RT-PCR for chondrogenic gene expression of aggrecan, type II collagen, and type I collagen. Cells labeled with a traceable green fluorescent protein (GFP) marker in vitro were suspended within the pads to analyze for dispersion and attachment to the pad. An in vivo study was performed in which full-thickness (3x4mm(2)) osteochondral defects were made in 60 rabbit knees. The study comprised four treatment groups based on the type of implant into the defect (empty, alginate alone, or either type of co-polymer pad) and harvested at either 6 or 12 weeks. Two independent blinded observers analyzed and scored the defects grossly and histologically. RESULTS: In vitro analysis of the chondrocytes after 1, 3, and 5 days in culture showed no statistical differences between the types of PGA/PLA co-polymer pad with regard to expression of aggrecan, type II collagen, or type I collagen. However, although statistically insignificant, the expression of aggrecan and type II collagen was found to be greater than that for type I collagen in both types of pads, confirming the chondrogenic effect of suspension culture for this system. The addition of alginate to polymer pads allowed costal chondrocytes to be implanted in vivo, as evidenced by the attachment of the cells to the fibers and the uniform dispersion of the GFP-labeled cells through the pad as seen on fluorescent microscopy. Histologic results showed improved scores for the 47.5/52.5 PGA-PLA group (21.3) and the 90/10 PGA-PLA group (18.3) when compared to empty (15.3) or alginate alone (15.1) defects at 12 weeks. CONCLUSION: The addition of calcium alginate to the co-polymer pads offers a new approach to deliver cells to an osteochondral defect and may enhance cartilage regeneration. Future application of this model may allow for an arthroscopic delivery system to assist the healing of cartilage defects.