Design of biomaterial and device for studying cartilage injury in vitro

Abstract

Articular cartilage covers the ends of bones in synovial joints, and undergoes 5000 loading cycles during a normal daily activity. This is over 108 loading cycles over an 80-year life span, which leads to mechanical wear and degeneration of the cartilage tissue resulting in pathologies such as Osteoarthritis (OA). OA is one of the most common forms of arthritis and is associated with functional limitations and pain for individuals with the disease. Various therapeutic interventions such as drugs and viscosupplements (artificial lubricants) are being developed to treat OA, but suffer from low residence time in the knee joint and/or inadequate distribution across and within the cartilage tissue. In this dissertation, I design a cationic branched poly lysine nanocarrier with many functional groups that can adhere and penetrate through full thickness cartilage tissue. This proof-of-concept study shows how the incorporation of cartilage interacting moieties such as cationic molecules can be used to enhance cartilage binding and can be leveraged for drug conjugation.Cartilage is naturally lubricated by synovial fluid which consists of diverse but unique molecules that work synergistically to reduce friction and wear from loading, and facilitates smooth joint loading. For example, highly hydrated hyaluronic acid (HA) interacts with lubricin to be localized at the surface of the cartilage. However, following joint injury and/or the onset of inflammatory joint diseases, composition of synovial fluid changes and its lubrication properties are compromised. The compromised synovial fluid is inadequate to provide lubrication and further contributes to cartilage degeneration. Intra-articular injections of high molecular weight viscosupplements, formulated with HA, are currently used to treat OA. Despite the importance of surface-adhered molecules in multiple modes of lubrication, current viscosupplements lack the ability to adhere to cartilage. Herein, I leverage these branched poly-lysine molecules to improve localization of HA molecules at the cartilage surface by conjugating BPL molecules into HA polymer chains. The BPL molecules present on the HA polymer chains interact with the cartilage tissue via electrostatic interactions. This study provides new insights into leveraging electrostatic interactions to improve lubricants, lubricant-cartilage interactions, and their role in different modes of lubrications. Finally, I have developed an in vitro “joint”-on-a-chip platform to recapitulate cartilage mechanical loading associated with various gait motions. Employing this platform, I studied how physiologic or hyperphysiologic mechanical loads affect cartilage health. While in this thesis research, I only examined the effect of mechanical loading on cartilage health this device can be applied to optimize the design of OA therapeutics, such as drugs or lubricants, before testing them in vivo. Overall, this dissertation offers new findings and design principles regarding scalable and easy to manufacture cationic branched poly-L-lysine molecules which can adhere and penetrate across cartilage tissue and its application to design cartilage adhering HA-based lubricants. I also developed microphyisiological model (Joint-on-Chip) that can accommodate explants and can be used to mimic various attributes of the knee joint. This device can be used as a screening platform, and reduce the dependence on animal models to study OA and discover therapeutics.