In vitro and in vivo neo-cartilage formation by heterotopic chondrocytes seeded on PGA scaffolds

Implantation of tissue-engineered heterotopic cartilage into joint cartilage defects might be an alternative approach to improve articular cartilage repair. Hence, the aim of this study was to characterize and compare the quality of tissue-engineered cartilage produced with heterotopic (auricular, nasoseptal and articular) chondrocytes seeded on polyglycolic acid (PGA) scaffolds in vitro and in vivo using the nude mice xenograft model. PGA scaffolds were seeded with porcine articular, auricular and nasoseptal chondrocytes using a dynamic culturing procedure. Constructs were pre-cultured 3 weeks in vitro before being implanted subcutaneously in nude mice for 1, 6 or 12 weeks, non-seeded scaffolds were implanted as controls. Heterotopic neo-cartilage quality was assessed using vitality assays, macroscopical and histological scoring systems. Neo-cartilage formation could be observed in vitro in all PGA associated heterotopic chondrocytes cultures and extracellular cartilage matrix (ECM) deposition increased in vivo. The 6 weeks in vivo incubation time point leads to more consistent results for all cartilage species, since at 12 weeks in vivo construct size reductions were higher compared with 6 weeks except for auricular chondrocytes PGA cultures. Some regressive histological changes could be observed in all constructs seeded with all chondrocytes subspecies such as cell-free ECM areas. Particularly, but not exclusively in nasoseptal chondrocytes PGA cultures, ossificated ECM areas appeared. Elastic fibers could not be detected within any neo-cartilage. The neo-cartilage quality did not significantly differ between articular and non-articular chondrocytes constructs. Whether tissue-engineered heterotopic neo-cartilage undergoes sufficient transformation, when implanted into joint cartilage defects requires further investigation.