This study covers the whole production cycle, from biodegradable polymer processing to an in vivo tissue engineered construct. Six different biodegradable polylactide 96/4 L/D single jersey knits were manufactured using either four or eight multifilament fiber batches. The properties of those were studied in vitro for 42 weeks and in 0- to 3-year shelf life studies. Three types (Ø 12, 15 and 19 mm) of cylindrical scaffolds were manufactured from the knit, and the properties of those were studied in vitro for 48 weeks. For the Ø 15 mm scaffold type, mechanical properties were also studied in a one-year in vivo experiment. The scaffolds were implanted in the rat subcutis. All the scaffolds were g-irradiated prior to the studies. In vitro, all the knits lost 99% of their mechanical strength in 30 weeks. In the three-year follow up of shelf life properties, there was no decrease in the mechanical properties due to the storage time and only a 12% decrease in molecular weight. The in vitro and in vivo scaffolds lost their mechanical properties after 1 week. In the case of the in vivo samples, the mechanical properties were restored again, stepwise, by the presence of growing/maturing tissue between weeks 3 and 12. Faster degradation was observed with in vitro scaffolds compared to in vivo scaffolds during the one-year follow up.

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The exact contribution of transplanted chondrocytes for cartilage tissue repair prior expansion in monolayer culures remains undetermined. At our laboratory, we have created a new permeable chamber to study the chondrogenesis of dedifferentiated cells implanted ectopically in a closed and controlled environment. The behavior of chondrocytes has been studied in settings frequently used in clinical approaches during transplantation, namely injection of autologous chondrocyte cells in suspension (ACI), cells soaked in collagen membranes (MACI), and cells applied in a polymer gel (fibrin). As controls, we have tested the redifferentiation of chondrocytes in cell aggregates, and we have checked the proper functionality of chambers both in vitro and in vivo. After retrieval, firmed tissue-like shapes were recovered only from chambers containing cells seeded in membranes. Histomorphological, immunohistochemical, and ultrastructural analyses revealed synthesis of fibrous-like tissue, characterized by low-density collagen fibers, low collagen type II, abundant collagen type I, and low amounts of proteoglycans. Additionally, neither the collagen membranes nor the fibrin gel was reabsorbed by cells. In summary, our results show that the newly developed permeable chambers function correctly, allowing proper cell feeding and preventing cell leakage or host cell invasion. Additionally, our results suggest that, under these circumstances, chondrocytes are not able to orchestrate formation of hyaline cartilage and have little capacity to degrade artificial membranes or carrier gels such as fibrin. These are interesting observations that should be considered for understanding what role the transplanted chondrocytes play during restoration of articular cartilage after implantation.

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