In vivo cartilage regeneration induced by a double-network hydrogel: Evaluation of a novel therapeutic strategy for femoral articular cartilage defects in a sheep model.

The purpose of this study was to establish the efficacy of a therapeutic strategy for an articular cartilage defect using a poly-(2-acrylamido-2-methylpropanesulfonic acid)/poly-(N,N'-dimethyl acrylamide) DN gel in a sheep model. Seventeen mature sheep were used in this study. We created a 6.0-mm osteochondral defect in the femoral trochlea of the patellofemoral (PF) joint and the medial condyle of the tibiofemoral (TF) joint. A cylindrical DN gel plug was implanted into the defect of the right knee so that a vacant space of the planned depths of 2.0 mm in group I, 3.0 mm in group II, and 4.0 mm in group III were left. In the left knee, we created a defect with the same depth as the right knee. The regenerated tissues were evaluated with the O'Driscoll score and real-time PCR analysis of the cartilage marker genes at 12 weeks. The DN gel implanted defect of group II in the PF and TF joints was completely filled with a sufficient volume of the proteoglycan-rich tissue stained with Safranin-O. The score showed that group II was significantly greater than groups I and III when treated with DN gel in the PF joint (p = 0.0441, p = 0.0174, respectively) and in the TF joint (p = 0.0019, p = 0.0006, respectively). This study has clarified the short-term efficacy of the cartilage regeneration strategy using the DN gel in a sheep model.