Cartilage tissue engineering: pioneering new approaches for the development of bioactive scaffolds with anatomically relevant morphologies

Abstract

Osteoarthritis is the leading cause of pain and disability worldwide. Progressive pathological changes in osteoarthritis are attributed to the fact that articular cartilage has a lack of vasculature, limiting its regenerative properties. Despite the availability of current treatment options, the prevalence of osteoarthritis is on the rise. Fully functional and suitable long-term treatments for large cartilage defects are yet to be sought. Over the years, considerable effort has been directed towards developing scaffolds for cartilage tissue engineering which consider the structural and biological function of the extracellular matrix (ECM). Tissue engineering combines structure, biological factors and signals to provide mechanical support and regulate cellular activities. This PhD focused on making scaffolds which captured the complex architecture and biological components of the native cartilage. To achieve this, a new technique called cyro-printing was developed to fabricate highly porous scaffolds with reproducible macro and micro pore structures. Through the adjustment of polymer solution concentration and print-head temperature, scaffold morphology, pore diameter and mechanical properties were altered. These cryo-printed scaffolds possess similar columnar pore structure as the deep zone of the cartilage.

Cryo-printing was then combined with electrospinning to produce multizone scaffolds which mimic the collagen fibre orientation in the various zones of the native cartilage. Multizone scaffolds provided a viable initial platform that captures the complex structure and compressive properties of the native cartilage. Moreover, they supported long-term chondrocyte and MSC attachment with expression of key chondrogenic genes and the production of the essential biomolecule, glycosaminoglycan. Investigation continued with the incorporation of bioactive molecules, collagen and antioxidants, into PCL scaffolds. Phase separated hybrid collagen and PCL scaffolds were produced that displayed an interconnected and porous structure with adequate mechanical properties. Interestingly, these properties could be altered with an increase in collagen concentration. The collagen was evenly distributed throughout the scaffold. These scaffolds successfully allowed chondrocyte attachment and viability. Vitamin E was then incorporated into PCL fibres with the aim to regulate oxidative stress. Electrospun vitamin E/PCL scaffolds were successfully produced which demonstrated antioxidant potential and the ability to support chondrocyte attachment and growth. Another antioxidant, glutathione was also combined with PCL and these scaffolds successfully allowed cell attachment and viability, as well as modulation of markers of oxidative stress.

Overall, the findings of this thesis demonstrate preliminary success with using scaffolds in vitro, highlighting their potential as platforms in cartilage tissue engineering.