Chondrocyte-based Repair of Articular Cartilage to Subchondral Bone
T. Shane Johnson, MD, Tamara K. Pylawka, MD, Sprague W. Hazard, MD, Greg S. Lewis, PhD, J. Spence Reid, MD, Henry J. Donahue, PhD.
Penn State Hershey Medical Center, Hershey, PA, USA.
Background: Articular cartilage injuries arising from repetitive or traumatic high impact loading are common. Repair strategies focus on creation of scar tissue, which is biomechanically inferior to articular cartilage. Previous studies have demonstrated the ability of tissue-engineered cartilage to bond to articular cartilage; however the ability to bond to subchondral bone is uncharacterized. The goal of this study is to characterize the bond formed between native cartilage, engineered cartilage and subchondral bone using histology and biomechanical testing.
Methods: Cartilage and subchondral bone discs (7 mm) were obtained from 6 month old swine. Chondrocyte sources (auricular, rib and articular cartilage) were minced into 1 mm3 fragments and digested using 0.1% type II collagenase. Chondrocytes were re-suspended in fibrin gel polymer (40x106 chondrocytes/mL) and the chondrocyte-fibrin gel suspension was placed between discs of articular cartilage and subchondral bone, forming tri-layered constructs which were placed into subcutaneous pockets in athymic mice for 6 and 12 weeks. Control constructs contained fibrin gel only. Samples were analyzed using immunohistochemistry, histology and biomechanical testing in tension. Statistical analysis was completed using ANOVA with Student-Newman-Keuls post hoc analysis. Significance was set at a p-value of <0.05.
Results: Experimental constructs from each group strongly expressed type II collagen suggesting not only chondrocyte viability but preserved synthetic function. Safranin-O revealed the presence of glycosaminoglycans in the newly formed tissue. Toluidine blue staining revealed the presence of strong protoglycan production. The ultimate stress supported by articular, auricular, costal and control constructs at 6 weeks was 180 ± 19 kPa, 156 ± 16, 166 ± 4 kPa and 104 ± 18 respectively. The ultimate stress supported by articular, auricular, costal and control constructs at 12 weeks was 289 ± 29 kPa, 338 ± 18, 256 ± 19 kPa and 155 ± 20 kPa respectively. The ultimate stress was significantly more at 12 weeks compared to 6 weeks when comparing each cell type. In addition each cell type had a significantly higher ultimate stress when compared to their respective control groups. The failure energy by articular, auricular, costal and control constructs at 6 weeks was 10 ± 0.37 kPa, 12 ± 1.6, 10 ± 1.6 kPa and 3.3 ± 0.75 respectively. The failure energy of articular, auricular, costal and control constructs at 12 weeks was 15 ± 9.3 kPa, 14 ± 4.6, 13 ± 7.5 kPa and 6.3 ± 2.7 kPa respectively. The failure energy was significantly more at 12 weeks compared to 6 weeks when comparing each cell type. In addition each cell type had a significantly higher ultimate stress when compared to their respective control groups.
Conclusions: This study demonstrates that chondrocytes harvested from ear, rib and joint sources generate new cartilage matrix containing type II collagen and glycosaminoglycans in vivo when suspended in fibrin gel. The newly synthesized matrix integrates with native articular cartilage and subchondral bone and forms mechanically functional bonds that strengthen over time. Chondrocyte based repair of articular cartilage defects may provide a functional alternative to current scar tissue based therapies for articular cartilage injury.
Back to Program