Biomechanical and Magnetic Resonance Characteristics of a Cartilage-like Equivalent Generated in a Suspension Culture

Abstract

Objective: To generate a cartilage biomaterial using a suspension culture with biophysical properties similar to native articular cartilage. Design: A novel cartilage tissue equivalent (CTE) using a no-scaffold, high-density suspension culture of neonatal porcine chondrocytes was formed on poly 2-hydroxyethyl methacrylate–treated plates for up to 16 weeks. Equilibrium aggregate modulus and hydraulic permeability were measured at 8 and 16 weeks using confined compression stress relaxation experiments. The CTE proteoglycan composition was characterized using sodium and T_1ρ magnetic resonance imaging methods after 8 weeks. Results: The resultant CTE produces a biomaterial consistent with a hyaline cartilage phenotype in appearance and expression of type II collagen and aggrecan. The equilibrium aggregate modulus and permeability for the 8-week specimens were 41.6 (standard deviation (SD) 4.3) kPa and 2.85^–13 (SD 2.45^–13) m⁴/Ns, respectively, and, for the 16-week specimens, 35.2 (SD 7.6) kPa and 2.67^–13 (SD 1.06^–13) m⁴/Ns, respectively. Average sodium concentration of the 8-week CTE ranged from 260 to 278mM and average T_1ρ relaxation times from 105 to 107 ms, indicating proteoglycan content similar to that of native articular cartilage. Conclusion: The high-density culture method produced a CTE with characteristics that approach those of native articular cartilage. The CTE mechanical properties are similar to those of the native cartilage. The CTE developed in this study represents a promising methodological advancement in cartilage tissue engineering and cartilage repair.