Joint injuries and associated diseases such as osteoarthritis place an immense socioeconomic burden on developed countries through consequences such as loss of work or costs associated with treatments. Whilst clinical strategies have been developed to treat joint defects, none have produced consistent positive results over a long-term. Alternate approaches have been explored in functional tissue engineering, with scaffold systems offering potential for healing of these osteochondral defects by inducing and guiding the desired tissue formation. In this thesis I aimed to develop scaffold systems and characterise assessment criteria for osteochondral tissue engineering.

I first explored melt-extruded polycaprolactone scaffolds in vitro under static and perfusive flow conditions. Scaffold groups shared structural porosity and varied in design, with four different architectures presented. I demonstrated a difference between groups in terms of mechanical response and fluid flow through the scaffolds, and confirmed that these differences affected osteoblast response in a cell culture under osteogenic conditions.

Secondly, I designed and constructed a hybrid zonal scaffold comprising a 3D-printed alginate-hydroxyapatite paste cast into a gelatine methacrylamide or gelatine methacrylamide/hyaluronic acid methacrylate blended hydrogel. This scaffold system was cultured in vitro with human articular chondrocytes, testing whether the formation of a zone of calcified cartilage was promotable. I found that whilst chondrogenic markers were upregulated throughout the culture in the hyaluronic acid-containing groups, there was no concrete evidence of the formation of a calcified region in this case. I postulated that with physical compression of the hydrogels during culture a greater effect may be seen in future work.

Thirdly, I developed a criterion on which to assess photocrosslinkable hydrogel systems in terms of cytotoxicity and hence optimise mechanical properties. Photocrosslinking proceeds through radical polymerisation under ultraviolet light, both components of which are toxic. I hypothesised that when a hydrogel has a greater number of reactive functional groups, these will selectively interact with the photoinitiator molecules and reduce cytotoxicity of the system. This was found to be the case when tested on human articular chondrocytes. I also tested the influence of two different ultraviolet light dosages on chondrogenic differentiation in vitro and found that at the chosen dosages there were no apparent effects, however both of the dosages were comparably cytocompatible.

Lastly, I tested gelatine methacrylamide, gellan gum and gellan gum methacrylate in various blends, using a relatively complex mechanical testing regimen to assess the tailorability of hydrogel viscoelasticity. Hydrogels were physically crosslinked (gellan gum) or chemically crosslinked (gelatine methacrylamide, gellan gum methacrylate) through photopolymerisation. I compared the viscoelastic properties of the hydrogels with those of native human cartilage explants and found that physically crosslinked hydrogels demonstrated the closest viscoelasticity however with a yielded highest elastic modulus with somewhat lower viscoelastic properties. Modulation of the ratio of physical and chemical crosslinks may be used in future to tailor material viscoelasticity to that of numerous biological tissues. Further examination of viscoelasticity as a criterion would provide a deeper understanding of the role of such mechanical properties in design of tissue engineering structures and its relevance in cartilage development.

Overall, my work demonstrated design of two scaffold systems within bone and osteochondral contexts, along with two characterisation methods that may be used to further develop tissue engineering structures for osteochondral regeneration.