Modular assembly for in vitro investigation and engineering of articular cartilage

Articular cartilage enables locomotion by protecting the ends of the long bones, providing a lubricated low-friction surface for movement, and absorbing and distributing force. It is also a tissue that is often damaged, and has poor intrinsic repair capacity, with damaged articular cartilage often progressing to osteoarthritis. Repair and regeneration of articular cartilage in order to generate structure and function identical to that of native tissue remains difficult. This demonstrates a need for repair strategies, and tissue engineering and regenerative medicine approaches hold promise as potential repair or regeneration methods. A modular approach to engineering of cartilage may allow separation of the tissue properties into components that can be individually optimised and recombined to a functional construct. Modular assembly is a process where separate components possessing separate functions are combined into a single, functional whole. Modular assembly of cartilage has potential to surmount some of the difficulties of articular cartilage repair and regeneration. In this thesis, I have demonstrated significant advancement of a modular assembly method to assemble tissues and a scaffold in an organised and controlled fashion. I have also shown separate optimisation of the tissue and scaffold components, investigated their interaction, and demonstrated enhanced modularity. This work highlights the potential for 3D tissue assembly in the development of clinically relevant cartilage tissue engineering repair strategies. Mass production of spheroidal microtissues by pellet culture was demonstrated in 96-well plates with minimal effect on chondrogenesis compared to standard tube-based pellet culture. Following this, the flexibility and novel capabilities of the 3D tissue assembly process was demonstrated given that microtissues were able to be arranged in a number of configurations within the 3D scaffold. Microtissue assembly was also shown to negate the surface properties of the scaffold surface. Since the quality of matrix formed was independent of the surface of the scaffold, this meant that modularity of the construct components was enhanced. A model for examining microtissue fusion was then developed, and interactions between microtissues were examined. The effects of soluble, physical and enzymatic factors on fusion were investigated, as well as the influence of cell type on fusion. Finally, appropriate scaffold fabrication with mechanical properties matched to native articular cartilage was achieved, while maintaining tissue module-friendly scaffold architecture. A modular construct was fabricated and assembled with tissue modules formed from human articular and nasal chondrocytes. The assembled constructs again demonstrated the desired mechanical properties in an assembled construct with immature tissue, and the process was able be scaled up to form larger constructs. These results demonstrate a modular assembled construct prepared for introduction to a load-bearing environment in vivo, and demonstrate that modular tissue engineering of articular cartilage has potential as a scalable repair strategy