Cartilage tissue engineers have made great inroads on understanding the factors controlling chondrogenesis, however, the biomechanical properties of tissue engineered cartilage (TEC) are chronically inferior to that of native cartilage. The focus of this dissertation was to determine the ability of scaffold-free TEC to withstand frictional shear stress, and if needed, to improve that ability to a physiologically relevant level.
Frictional-shear testing performed at a sub-physiological normal stress of 0.55 MPa demonstrated that constructs exhibited lubrication patterns characteristic of native cartilage lubrication, but severe damage also occurred. Low absolute collagen content, and a low collagen-to-glycosaminoglycan (GAG) ratio were also found in the same constructs. Reduction in damage was attempted by increasing the collagen content of the ECM.
Scaffold-free TEC treated with T4 at 25 ng/ml exhibited increased collagen concentration in a statistically significant manner, and the average collagen-to-GAG ratio was also increased although statistical significance was not achieved. Western blotting showed that type Il collagen was increased, type X collagen was not detected. COL2A1, and biglycan gene expression were also found to have increased, no statistically significant difference was found for COLX gene expression.
When compared to control constructs, T4 treated constructs exhibited a large and statistically significant decrease in the extent of damage incurred by frictional-shear testing. At the 2.8 MPa normal stress, total damage was reduced by 60% in the 2-month constructs.
Correlation coefficients calculated between compositional properties and the amount of damage showed that at the 2.8 MPa normal stress collagen concentration and the collagen-to-GAG ratio exhibited the greatest correlation to damage (correlation coefficient of approximately -0.7 with a 95% confidence interval of approximately -0.87 to -0.38 for both).
In conclusion, scaffold-free cartilage generated without special attention to increasing collagen content may be highly susceptible to damage from frictional-shear stress. Furthermore, the collagen-to-GAG ratio appears to be an important property in determining damage susceptibility. Collagen content can be improved by use of T4. Presumably as a result of the increased collagen content, scaffold-free TEC treated with T4 was able to withstand frictional-shear testing at physiologically relevant normal stresses.
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