Nutrient Channels Aid the Growth of Articular Surface-Sized Engineered Cartilage Constructs

Symptomatic osteoarthritic lesions span large regions of joint surfaces and the ability to engineer cartilage constructs at clinically relevant sizes would be highly desirable. We previously demonstrated that nutrient transport limitations can be mitigated by the introduction of channels in 10mm diameter cartilage constructs. In this study, we scaled up our previous system to cast and cultivate 40mm diameter constructs (2.3mm overall thickness); 4mm diameter and channeled 10mm diameter constructs were studied for comparison. Furthermore, to assess whether prior results using primary bovine cells are applicable for passaged cells-a more clinically realistic scenario-we cast constructs of each size with primary or twice-passaged cells. Constructs were assessed mechanically for equilibrium compressive Young's modulus (E-Y), dynamic modulus at 0.01 Hz (G*), and friction coefficient (mu); they were also assessed biochemically, histologically, and immunohistochemically for glycosaminoglycan (GAG) and collagen contents. By maintaining open channels, we successfully cultured robust constructs the size of entire human articular cartilage layers (growing to similar to 52 mm in diameter, 4mm thick, mass of 8 g by day 56), representing a 100-fold increase in scale over our 4mm diameter constructs, without compromising their functional properties. Large constructs reached E-Y of up to 623 kPa and GAG contents up to 8.9%/ww (%of wet weight), both within native cartilage ranges, had G* >2 MPa, and up to 3.5%/ww collagen. Constructs also exhibited some of the lowest m reported for engineered cartilage (0.06-0.11). Passaged cells produced tissue of lower quality, but still exhibited native E-Y and GAG content, similar to their smaller controls. The constructs produced in this study are, to our knowledge, the largest engineered cartilage constructs to date which possess native E-Y and GAG, and are a testament to the effectiveness of nutrient channels in overcoming transport limitations in cartilage tissue engineering.