Fibrin-based model for cartilage regeneration: tissue maturation from in vitro to in vivo

One of the crucial points for a successful tissue-engineering approach for cartilage repair is represented by the level of in vitro maturation of the engineered tissue before implantation. The purpose of this work was to evaluate the effect of the level of in vitro maturation of engineered cartilaginous samples on the tissue quality after in vivo implantation. Samples were obtained from isolated swine articular chondrocytes embedded in fibrin glue. The cell-fibrin composites were either cultured in vitro or directly implanted in vivo for 1, 5, and 9 weeks. Other experimental samples were precultured for either 1 or 5 weeks in vitro and then implanted in vivo for 4 additional weeks. All the samples were analyzed by histology, immunohistochemistry, biochemistry, and gene expression. The results strongly suggest that the in vivo culture in this model promoted a better tissue maturation than that obtained in the in vitro condition, and that 1 week in vitro preculture resulted in the primary structuring of the engineered composites and their subsequent maturation in vivo, without affecting the cell viability and activity, while a prolonged in vitro preculture caused a cell and matrix degeneration that could not be rescued in vivo.