Experimental and Theoretical Evaluation of Failure Properties for Immature Tissue Engineered Cartilage

Articular cartilage functions as a low friction load bearing soft tissue. The contact area and load distribution is highly location dependent in the knee joint [1]. Regeneration and repair strategies for osteoarthritis include tissue-engineered cartilage, which will need to bear high mechanical stresses and strains. There has been variable success in developing tissue-engineered cartilage with compressive mechanical properties comparable to native tissue (modulus = 40kPa – 1000kPa) [2–4]. There has also been some debate on the costs and benefits of implanting immature constructs and allowing them to elaborate their properties in situ, or culturing them in vitro and implanting them only after they have elaborated sufficiently functional properties. The former strategy may benefit from using the body as a bioreactor and might promote better construct integration, though constructs may bee to frail to sustain the physiological loading environment. The failure properties of engineered cartilage have not been widely evaluated, and may greatly affect the successful implantation of engineered cartilage as a repair strategy for the knee joint. The objective of this study was twofold: 1) to evaluate the failure properties of agarose hydrogels used as scaffolds in our tissue engineering studies, and 2) to evaluate whether joint congruence might sufficiently shield immature constructs to prevent their early failure. The long-term hypothesis of this study is that engineering analyses, based on an informed failure criterion for tissue constructs, might allow proper pre-assessment of failure risk for a given set of construct properties, dimensions, and joint congruence.