Osteoarthritis (OA), the most prevalent form of joint disease, afflicts nine percent of the US population over the age of thirty and costs the economy nearly $100 billion annually in healthcare and socioeconomic costs. It is characterized by joint pain and dysfunction, though the pathophysiology remains largely unknown. The progressive loss of cartilage followed by inadequate repair and remodeling of subchondral bone are common hallmarks of this degenerative disease. Due to its avascular nature and limited cellularity, articular cartilage exhibits a poor intrinsic healing response following injury. As such, significant research efforts are aimed at producing engineered cartilage as a cell-based approach for articular cartilage repair. However, the knee joint is mechanically demanding, and during injury, also a milieu of harsh inflammatory agents. The unforgiving mechanochemical environment requires constructs that are capable of bearing such burdens.

To this end, previous work in our laboratory has explored the application of stimuli inspired by the native joint environment in attempts to create tissue with functional properties similar to native cartilage so that it may restore loading to the joint. While we have had success at producing these replacement tissues, there is little evidence in the literature that the biological functionality (i.e. response to in vivo-like conditions) of engineered cartilage matches native cartilage. Therefore, in an effort to provide a more complete characterization of the functional nature of developing tissues and facilitate their use clinically, the overarching motivation of the work described in this dissertation is two-fold:​ 1) characterize the response of engineered cartilage to chemical and mechanical injury;​ and 2) develop strategies for enhancing the performance and protection of engineered cartilage for in vivo success.

Studies in the literature have extensively characterized the effects of wounding to native articular cartilage as well as the effects of an inflammatory environment. For mechanical injuries, cell death is immediate and progressive, ultimately leading to failure of the tissue. Chemical insult has been shown to promote degradation of the matrix components, also leading to failure of the tissue. Under a controlled application of injury (mechanical and chemical), it was found that engineered cartilage, in contrast to native cartilage, has the potential to repair itself following an injury event, as long as there is no catastrophic damage to the matrix. Additionally, when this matrix is intact and well-developed, engineered cartilage constructs exhibit a resistance to degradation, highlighting the potential utility of engineered cartilage as replacement tissues.

Enhancing functionality in engineered cartilage was also explored, with the aim of developing strategies to improve, repair, and protect engineered cartilage constructs for their use in vivo. For these purposes, the studies in this dissertation spanned both 2D migration studies to influence the limited wound repair potential of cells as well as 3D culture studies to explore the possibility of protection effects at a tissue level. Together, these models allowed us to capture the complexity needed to fully develop approaches for cartilage repair. Though it has previously been found that applied DC electric fields modulate cell migration, we have developed a novel strategy of employing this technique to screen for desirable populations of cells (those with the greatest capacity for directed migration) to use in cartilage repair. We also found that the AQP1 water channel plays a key role in mechanosensing the extracellular environment, highlighting the potential for its use in therapeutic strategies.

For tissue engineering efforts at creating functional cartilage replacement, we uncovered novel strategies to foster better tissue development via co-culture systems and promote the resistance of engineered cartilage to catabolic factors. These findings motivate their potential use in therapeutics and in tissue engineering efforts at creating clinically-relevant tissue-engineered constructs for the treatment of OA or following injury.

The research described in this dissertation has characterized the biological functionality of engi- neered tissues and identified strategies for enhancing their use in vivo by modulating the subsequent response to injury, laying the foundation for their use in clinical applications.