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Note: thesis: Thesis (Sc. M.)--Brown University, 2017
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Abstract: Introduction: Osteoarthritis is a debilitating joint disease that affects over 27 million Americans. Tissue engineered cartilage could be a viable option for patients that have lost cartilage due to injury or osteoarthritis. However, reaching optimal mechanical and biochemical properties in tissue engineered cartilage is still a challenge. This study investigates the dose-dependent effects of compressive loading on chondrocyte seeded agarose hydrogels over a 6-week study. Our hypothesis is that early high compressive loading will enhance GAG deposition. Methods: Primary chondrocytes were isolated from porcine knees and digested in 0.15% Collagenase Type II overnight at 37°C. Cells were suspended in 2% agarose and punched into discs with final dimensions was 4 mm diameter and 1.5 mm thick. After two weeks of static culture in chondrogenic media with TGF-β and Dexamethasone, dynamic loading was applied with a 5% tare strain followed by 10% or 30% dynamic compressive loading, or a combination of the two, at 1 Hz for 3hrs/day and 5 days/week for four weeks. The data was analyzed using ANOVA with Tukey Method with a confidence of 95%. Results: On day 28, samples loaded with 30% strain showed significantly higher GAG/ dry weight than samples that were cultured in free-swell. On day 42, there was no significant difference between groups and there was a significant decrease in GAG when compared to day 28. Group loaded with 30% strain and then 10% (group 30/10) had significantly higher DNA/ dry weight than any group on day 42. However, there was no significant difference in DNA between groups in the initial 2 weeks of mechanical loading (day 28 of culture). Group 30/10 also had significantly higher collagen per dry weight than the free-swell group, however as seen with GAG, there was also a decrease in collagen for all groups when compared to day 28. There was no significant difference in collagen between groups after 2 weeks of mechanical loading (day 28 of culture). Equilibrium modulus (EM) increased for all groups between day 14 and day 28 of culture but decreased during day 42. On day 28, samples that received no loading and samples that received 10% strain had significantly higher EM than groups loaded with 30% strain. On day 42, group 10/10 had significantly higher EM than the free-swell group. Discussion: Dynamic loading significantly enhanced GAG production by chondrocytes in the first 28 days of culture. The samples were able to reach EM values consistent with native cartilage (60-250kPa) in the first 28 days. After 28 days, there was a decrease in GAG, collagen, and equilibrium modulus in all the groups. However, DNA production increased after 28 days indicating cell death did not contribute to the decrease in GAG, collagen, and mechanical properties. The results could indicate a decrease in chondrogenic characteristics. Although the data failed to prove the hypothesis, it did suggest that subjecting the samples with a strain of 30% and then 10% could lead to higher DNA and collagen deposition than freeswell.
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Identifier: DOI: 10.7301/Z0TB15CB
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