Analysis of radial variations in material properties and matrix composition of chondrocyte-seeded agarose hydrogel constructs

Objective: To examine the radial variations in engineered cartilage that may result due to radial fluid flow during dynamic compressive loading. This was done by evaluating the annuli and the central cores of the constructs separately. Method. Chondrocyte-seeded agarose hydrogels were grown in free-swelling and dynamic, unconfined loading cultures for 42 days. After mechanical testing, constructs were allowed to recover for 1-2 h, the central 3 mm cores removed, and the cores and annuli were retested separately. Histological and/or biochemical analyses for DNA, glycosaminoglycan (GAG), collagen, type I collagen, type 11 collagen, and elastin were performed. Multiple regression analysis was used to determine the correlation between the biochemical and material properties of the constructs. Results: The cores and annuli of chondrocyte-seeded constructs did not exhibit significant differences in material properties and GAG content. Annuli possessed greater DNA and collagen content over time in culture than cores. Dynamic loading enhanced the material properties and GAG content of cores, annuli, and whole constructs relative to free-swelling controls, but it did not alter the radial variations compared to free-swelling culture. Conclusion: Surprisingly, the benefits of dynamic loading on tissue properties extended through the entire construct and did not result in radial variations as measured via the coring technique in this study. Nutrient transport limitations and the formation of a fibrous capsule on the periphery may explain the differences in DNA and collagen between cores and annuli. No differences in GAG distribution may be due to sufficient chemical signals and building blocks for GAG synthesis throughout the constructs. (c) 2008 Published by Elsevier Ltd on behalf of Osteoarthritis Research Society International.